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Parasites increase fluctuating asymmetry of male Drosophila nigrospiracula: Implications for sexual selection
Abstract
Fluctuating asymmetry (minor deviations from perfect bilateral symmetry) is manifested by individuals less able to buffer
environmental stress during development. I utilized a system of two naturally-occurring parasites ofDrosophila nigrospiracula to test whether parasitic infection during host development yields elevated degrees of fluctuating asymmetry in two morphological
traits of males. This hypothesis has important implications for sexual selection, as it may explain why asymmetric males are
often found to be sexually disadvantaged. In my system, nematodes infect larvae and therefore are more likely to disrupt development
than mites which only parasitize adult flies. As predicted, nematode-infected maleD. nigrospiracula had a higher degree of bristle asymmetry than did mite-infested and control (carrying neither parasite) males. There was
also a significant relation between nematode number and degree of asymmetry. There was a significant negative relation between
nematode load and size of adult males, implicating a causal link between nutritional stress during host development and fluctuating
asymmetry. Patterns of wing length asymmetry were inconsistent with those of bristle asymmetry. Nematode-infected males did
not differ in wing length asymmetry relative to mite-infested and control males, nor was there a significant relation between
nematode number and wing asymmetry. This inconsistency in expression of asymmetry may reflect different intensities of selection
operating on each morphological trait.
... Second, individuals with higher levels of FA may more often be exposed to parasites; if competitive ability depends on body condition, developmentally unstable individuals will more often be restricted to poor environments with elevated risk of encountering parasites [14,52,54,55]. Third, parasites may disrupt host development and be the direct cause of instability [52]; host FA should be directly related to parasite virulence, parasite load, or both [54,[56][57][58]. ...
... Observed ontogenetic trend in mandibular shape FA in P1 category correspond to that identified within the whole sample for age categories, i.e. the level of DS for mandibular shape increases with age. If parasites directly act on the developmental stability of their hosts by imposing on them a metabolic cost during their ontogeny [52,56], it is predicted that host developmental instability should be directly related to parasite virulence, parasite load, or both [54,[56][57][58]. Therefore, it seems likely that the detected relationship between cranial shape DS and nematode infections in A. flavicollis is caused by parasitic disruption of host development and their direct effect on host DS, i.e. by the third reason proposed by Møller [52]. ...
... Observed ontogenetic trend in mandibular shape FA in P1 category correspond to that identified within the whole sample for age categories, i.e. the level of DS for mandibular shape increases with age. If parasites directly act on the developmental stability of their hosts by imposing on them a metabolic cost during their ontogeny [52,56], it is predicted that host developmental instability should be directly related to parasite virulence, parasite load, or both [54,[56][57][58]. Therefore, it seems likely that the detected relationship between cranial shape DS and nematode infections in A. flavicollis is caused by parasitic disruption of host development and their direct effect on host DS, i.e. by the third reason proposed by Møller [52]. ...
Background
Mammalian mandible and cranium are well-established model systems for studying canalization and developmental stability (DS) as two elements of developmental homeostasis. Nematode infections are usually acquired in early life and increase in intensity with age, while canalization and DS of rodent skulls could vary through late postnatal ontogeny. We aimed to estimate magnitudes and describe patterns of mandibular and cranial canalization and DS related to age and parasite intensity (diversity) in adult yellow-necked mice (Apodemus flavicollis).
Results
We found the absence of age-related changes in the levels of canalization for mandibular and cranial size and DS for mandibular size. However, individual measures of mandibular and cranial shape variance increased, while individual measures of mandibular shape fluctuating asymmetry (FA) decreased with age. We detected mandibular and cranial shape changes during postnatal ontogeny, but revealed no age-related dynamics of their covariance structure among and within individuals. Categories regarding parasitism differed in the level of canalization for cranial size and the level of DS for cranial shape. We observed differences in age-related dynamics of the level of canalization between non-parasitized and parasitized animals, as well as between yellow-necked mice parasitized by different number of nematode species. Likewise, individual measures of mandibular and cranial shape FA decreased with age for the mandible in the less parasitized category and increased for the cranium in the most parasitized category.
Conclusions
Our age-related results partly agree with previous findings. However, no rodent study so far has explored age-related changes in the magnitude of FA for mandibular size or mandibular and cranial FA covariance structure. This is the first study dealing with the nematode parasitism-related canalization and DS in rodents. We showed that nematode parasitism does not affect mandibular and cranial shape variation and covariance structure among and within individuals. However, parasite intensity (diversity) is related to ontogenetic dynamics of the levels of canalization and DS. Overall, additional studies on animals from natural populations are required before drawing some general conclusions.
... 2. Stress generally increases FA of traits (vs. no or trait-specific increases; e.g., Beardmore 1960;Waddington 1960;Parsons 1961;Polak 1993;Hurtado et al. 1997). Hypotheses about interactions between trait variability and FA: ...
... Bristle character CVs were typically four to five times higher than wing trait CV s, and among the latter wing length CV s were lower than cross vein CVs. Similar observations on these types of traits have been reported for other invertebrate species (Polak 1993;Clarke 1995). Trait differences in CVs may reflect selection. ...
... In contrast to earlier work (Parsons 1961(Parsons , 1962Polak 1993;Imasheva et al. 1997), the FA of sternopleural bristles was not a reliable indicator of stress. There are three possible reasons for this. ...
A number of hypotheses have been proposed about the association between developmental stability phenotypic variability, heritability, and environmental stress. Stress is often considered to increase both the asymmetry and phenotypic variability of bilateral traits, although this may depend on trait heritability. Empirical studies of such associations often yield inconsistent results. This may reflect the diversity of traits and conditions used or a low repeatability of any associations. To test for repeatable associations between these variables, multiply replicated experiments were undertaken on Drosophila melanogaster using a combination stress at the egg, larval and adult stages of reduced protein, ethanol in the medium, and a cold shock. Both metric and meristic traits were measured and levels of heritable variation for each trait estimated by maximum likelihood and parent-offspring regression over three generations. Trait means were reduced by stress, whereas among-individual variation increased Fluctuating asymmetry (FA) was increased by stress in some cases, but few comparisons were significant. Only one trait orbital bristle, showed consistent increases in FA. Changes in trait means, trait phenotypic variability, and developmental stability as a result of stress were not correlated. Extreme phenotypes tended to have higher levels of FA but only the results for orbital bristles were significant. All traits had low to intermediate heritabilities except orbital bristle, which showed no heritable variation. Only traits with low heritability and high levels of phenotypic variability may show consistent increases in FA under stress. Overall, the independence of phenotypic variability, plasticity, and the developmental stability of traits extend to changes in these measures under stressful conditions.
... There is evidence that secondary compounds e.g. 26 , parasites e.g. 27 , temperature e.g. 17 and inbreeding e.g. 28 may affect different morphological traits in their size and/or shape as confirmed in our results. ...
... Although parasites can have a considerable impact on bees 36 and interfere with their larval development 37 , the relationship among size, shape and parasitic prevalence has rarely been assessed 27 . Here we highlighted that infested bumblebees were significantly smaller than non-infested ones in the same rearing conditions. ...
Abstract Human activities can generate a wide variety of direct and indirect effects on animals, which can manifest as environmental and genetic stressors. Several phenotypic markers have been proposed as indicators of these stressful conditions but have displayed contrasting results, depending, among others, on the phenotypic trait measured. Knowing the worldwide decline of multiple bumblebee species, it is important to understand these stressors and link them with the drivers of decline. We assessed the impact of several stressors (i.e. natural toxin-, parasite-, thermic- and inbreeding- stress) on both wing shape and size and their variability as well as their directional and fluctuating asymmetries. The total data set includes 650 individuals of Bombus terrestris (Hymenoptera: Apidae). Overall wing size and shape were affected by all the tested stressors. Except for the sinigrin (e.g. glucosinolate) stress, each stress implies a decrease of wing size. Size variance was affected by several stressors, contrary to shape variance that was affected by none of them. Although wing size directional and fluctuating asymmetries were significantly affected by sinigrin, parasites and high temperatures, neither directional nor fluctuating shape asymmetry was significantly affected by any tested stressor. Parasites and high temperatures led to the strongest phenotype modifications. Overall size and shape were the most sensitive morphological traits, which contrasts with the common view that fluctuating asymmetry is the major phenotypic marker of stress.
... The elevated level of FA in flies dead from the entomopathogenic fungus is thus in accordance with this expectation (Table 3). Parasitism has previously been shown to be associated with developmental stability (Mlilller 1992c;Polak 1993). Mlilller (1992c) demonstrated experimentally that the presence of one haematophagous ectoparasite subsequently gave rise to increased FA in a secondary sexual character, but not in two ordinary morphological characters. ...
... Nematodes infecting Drosophila nigrospiracula larvae ap- * Statistically significant at P < 0.05. peared to cause increased levels of abdominal bristle asymmetry in adult flies, implicating a causal relationship between nutritional stress during host development and fluctuating asymmetry (Polak 1993). In conclusion, these two studies indicate that large levels of FA develop as a consequence of parasite infections. ...
Associations between developmental stability, sexual selection, and viability selection were studied in the domestic fly Musca domestica (Diptera, Muscidae). Developmental stability of the wings and tibia of flies of both sexes, measured in terms of their level of fluctuating asymmetry, was positively associated with mating success in free ranging populations and in sexual selection experiments. Mated individuals may have obtained indirect fitness benefits from sexual selection of two different kinds. First, the entomopathogenic fungus Enthomophthora muscae (Zygomycetes, Entomophthorales) infects and kills adult domestic flies, and flies dead from fungus infections had more asymmetric wings than flies dead for other reasons. Experimental deposition of fungus spores on uninfected flies demonstrated that flies with asymmetric wings were more susceptible to fungus infections than flies with symmetric wings. Second, domestic flies were frequently eaten by insectivorous barn swallows Hirundo rustica, and flies depredated by birds had more asymmetric wings and tibia than surviving flies.
... However, not every trait shows an increase in fluctuating asymmetry with increased stress; different traits appear to be under different levels of stabilizing selection. Many morphological traits, especially those used in functions related to survival, are highly canalized and therefore are less susceptible to developmental disturbance (Polak 1993). Other traits seem to be much more susceptible to stress. ...
... This leads to the hypothesis that fluctuating asymmetry and sexual selection are related as follows: low levels of fluctuating asymmetry in a male may indicate a male's heritable ability to cope with stress, so a female should choose to mate with a more symmetrical male to increase her offspring's viability and, in turn, her fitness. An alternative hypothesis, for the case of disease-or parasite-induced fluctuating asymmetry, is that a female should choose to mate with a more symmetrical male to gain the direct benefit of avoiding parasite or disease transmission (Polak 1993). These ideas lead to predicted patterns of fluctuating asymmetry in ornamental traits. ...
Fluctuating asymmetry, random departure from perfect symmetry in bilateral traits, has been proposed as an indirect indicator of individual quality. Sexually selected traits, such as deer antlers, are hypothesized to demonstrate decreasing level of fluctuating asymmetry with increasing trait size and decreasing level of fluctuating asymmetry with increasing age. These hypotheses have been previously tested for antlers using linear measurements to quantify fluctuating asymmetry. However, antlers are complex, 3-dimensional traits making it difficult to quantify all forms of visual asymmetry using traditional, linear measurements. It is this visual asymmetry that would be assessed by potential mates and rivals. Therefore, we created 3-dimensional computer models of white-tailed deer (Odocoileus virginianus) antlers to measure visual fluctuating asymmetry. Asymmetry measures of various antler traits were computed using the models by measuring distances from the trait to a vertical and horizontal plane created using coordinate points generated within the model. We found no association between degree of fluctuating asymmetry and trait size, nor was any association found between degree of fluctuating asymmetry and age using either the 3-dimensional measures of asymmetry or traditional, linear measures of asymmetry. Examination of these data suggests that fluctuating asymmetry of white-tailed deer antlers is not a reliable indicator of quality.
... Results implied that presence of parasite affects fluctuating asymmetry in host species. This is consistent with other studies where parasitism has significant effect on the degree of fluctuating asymmetry on the host (Moller 1992;Polak 1993). The mechanisms by which parasites cause increased character asymmetry in general and for Sardinella sp. in particular are unknown and still subject to further investigations though there were underlying pre-conceived notions. ...
... The mechanisms by which parasites cause increased character asymmetry in general and for Sardinella sp. in particular are unknown and still subject to further investigations though there were underlying pre-conceived notions. But most likely, parasite-induced nutritional deprivation of various forms destabilizes host development and elevates levels of fluctuating asymmetry (Polak 1993(Polak , 1997. Parasitism can limit host nutrient availability by reducing host food intake, digestion, absorption and nutrient assimilation (Whitefield 1979;Thompson 1983;Polak 1997). ...
Fluctuating asymmetry (FA) is defined as subtle, random deviation from perfect symmetry and is the most commonly used estimate of developmental stability. It has been found to increase with the presence of stressors including parasite infestation. In this study, potential relationships were investigated between the presence of parasite and its effect to FA as a widely employed measure of developmental stability on Sardinella sp. FA levels as asserted in many studies increases with developmental instability. Sardinella sp. from Misamis Oriental were collected and assessed for the presence of parasites in the gills. Fluctuating asymmetry in the traits were analyzed using landmark method for shape asymmetry, via Symmetry and Asymmetry in Geometric Data (SAGE) program. A total of twelve landmark points were used and a total of 200 fishes were evaluated. Procrustes ANOVA showed insignificant levels of FA for Sardinella sp. found without parasite while those found with parasites showed significant levels of FA. Thus, in consistency with other studies, that the presence of parasites may affect the developmental stability of an organism as seen in the asymmetry measurement of the left and right sides of the organism, which implies the extent to which the organism is able to buffer any disturbance. Hypothesis assumes that parasites can cause an increased level of FA due to the stress it induced in the development of the organism. An increase level of FA has implications on species fitness and adaptation. Presence of parasites has negative impact on host fitness.
... We hypothesized that female abdominal melanized spots could be related to mating, through either external damage from the male or an internal physiological response to mating, although there was only a weak non-significant positive relationship between the presence of ventral abdominal wounding and copulatory wounding. Another possible explanation for the presence of melanized spots on the ventral abdomen is that this is one of the dominant mite attachment sites, a finding that aligns with other Drosophila studies [52,53]. We observed melanized wounds in three-quarters of the flies that had their mites removed, and wounds with a similar appearance were found in our fly wounding survey. ...
Wounding occurs across multicellular organisms. Wounds can affect host mobility and reproduction, with ecological consequences for competitive interactions and predator–prey dynamics. Wounds are also entry points for pathogens. An immune response is activated upon injury, resulting in the deposition of the brown-black pigment melanin in insects. Despite the abundance of immunity studies in the laboratory and the potential ecological and evolutionary implications of wounding, the prevalence of wounding in wild-collected insects is rarely systematically explored. We investigated the prevalence and potential causes of wounds in wild-collected Drosophilidae flies. We found that 31% of Drosophila melanogaster were wounded or damaged. The abdomen was the most frequently wounded body part, and females were more likely to have melanized patches on the ventral abdomen, compared with males. Encapsulated parasitoid egg frequency was approximately 10%, and just under 1% of Drosophilidae species had attached mites, which also caused wounds. Wounding is prevalent in D. melanogaster, likely exerting selection pressure on host immunity for two reasons: on a rapid and efficient wound repair and on responding efficiently to opportunistic infections. Wounding is thus expected to be an important driver of immune system evolution and to affect individual fitness and population dynamics.
... Many previous studies have shown that FA level in insects is not always directly proportional to all environmental or genetic stresses. Many studies report an increase in FA level under some environmental stress factors such as nutritional stress (Imasheva et al. 1999), chemicals (Abaga et al. 2011), temperature (Chapman and Goulson , parasitic infection (Polak 1993), genetic stress factors such as homozygosity (Messier and Mitton 1996), hybridization (Ross and Robertson 1990), or inbreeding (Carter et al. 2009). Moreover, some studies did not demonstrate considerable changes in the level of FA caused by environmental or genetic stress (Clarke et al. 1986;Fowler and Whitlock 1994;Chapman and Goulson 2000;Jones et al. 2005;Carter et al. 2009;Vijendravarma et al. 2011). ...
... Many previous studies have shown that FA level in insects is not always directly proportional to all environmental or genetic stresses. Many studies report an increase in FA level under some environmental stress factors such as nutritional stress (Imasheva et al. 1999), chemicals (Abaga et al. 2011), temperature (Chapman and Goulson , parasitic infection (Polak 1993), genetic stress factors such as homozygosity (Messier and Mitton 1996), hybridization (Ross and Robertson 1990), or inbreeding (Carter et al. 2009). Moreover, some studies did not demonstrate considerable changes in the level of FA caused by environmental or genetic stress (Clarke et al. 1986;Fowler and Whitlock 1994;Chapman and Goulson 2000;Jones et al. 2005;Carter et al. 2009;Vijendravarma et al. 2011). ...
The present study aimed to determine the wing asymmetry and sexual asymmetry of Pantala flavescens (Fabricius 1798) collected from a paddy field. P. flavescens is known as the longest migratory insect species and the morphological architecture of their hindwing aids in long-distance gliding. In our study, we collected F1 generation of male and female P. flavescens and used for geometric morphometric study to investigate wing asymmetry. We observed no difference in wing size between sexes from the study, but there are significant (p < 0.05) shape differences. The female population was more asymmetric than male population, with a high shape-related fluctuation asymmetry (FA). Discriminant function analysis was used to validate wing asymmetry (right-left) and sexual asymmetry of P. flavescens. Canonical variant analysis discriminated the forewings and hindwings of P. flavescens both sexes in a distinct morphospace. The PC’s warp shape analysis proved that, when compared to forewings, the highest amount of shape variations was observed in hindwings, especially in anal lobe regions. Based on the results, pesticide and fertilizer used in the paddy fields are the primary reason for the high level of FA, and the morphological variations observed in the hindwings may influence the migratory behaviour of P. flavescens.
... The mechanisms by which parasites cause increased asymmetry in fishes and for N. japonicus in particular are still subject to further studies though there were some acceptable ideas that could explain the effect of parasites in their hosts. One of the plausible explanations for this is that parasites can limit host nutrient availability by reducing host food intake, digestion, absorption and nutrient assimilation, resulting to nutritional deprivation of various forms, destabilizes host development and eventually elevates the levels of fluctuating asymmetry (Polak, 1994). In addition, parasites compete with their hosts for resources, and therefore invade upon host metabolism that can reduce the growth and development of its host species (Goater et al., 1993). ...
Nemipterus japonicusis one of the most convenient hosts in studying parasites because of its association with polluted marine ecosystems making it as more susceptible to parasitism. Herein, the effect of endoparasites in the length-weight relationship (LWR) and developmental stability of N. japonicuswere investigated through the use of linear regression analysis and fluctuating asymmetry (FA), respectively. There were 30 infected and 30 non-infected samples of N. japonicuscollected from the two sites in Mindanao, Philippines then measured morphometrically and examined parasitologically. Results showed that four species of endoparasites were found in the intestine of N. japonicus, with Acanthocephalussp. as the most abundant, most prevalent and has the highest mean intensity in Sangali while Anisakissp. in Maluso. Linear regression analysis revealed that all of the samples collected from the two sites exhibit negative allometric growth pattern (b<3.0), strongly correlated (r>0.70) and found to be highly significant (P<0.05), indicatingthat as the body length of N. japonicusincreases; its body weight becomes less rotund. The Procrustes Analysis of Variance (ANOVA) showed insignificant levels of FA for non-infected N. japonicuswhile those infected N. japonicusyieldsignificant FA value (p<0.001) forboth sites, implying that the presence of parasites can affect the developmental stability of N. japonicus. Findings suggest that parasites can increase the levels of FA due to the stress it induced in the development of the organism and demonstrates that LWR and FA are useful tools in studying the conditions of fish populations in their habitat.
... Comparing the chemical composition of sugar cane with honey, it could be detected that the sugar cane has only one type of sugar, sucrose, in comparison with honey which has many types of sugars, amino acids, minerals, enzymes, hormones, vitamins, organic acids, and natural antibiotics in its components (Herold, 1982). So, sucrose syrup as artificial feeding might be one of nutritional stresses which are responsible of development instability (Polak, 1993). However, most of beekeepers cannot dispense with using artificial sugar feeding to feed their colonies, since it is used to supplement a shortage of stored honey to prevent starvation of the colony, or to stimulate a colony to artificially promote breeding. ...
... Comparing the sugar cane with honey, it could detect that the sugar cane has only sucrose, in comparison with honey which has many types of sugars, amino acids, minerals, enzymes, hormones, vitamins, organic acids, and natural antibiotics in its components (Herold, 1982). So, sucrose syrup as artificial feeding might be one of nutritional stresses which are responsible of development instability (Polak, 1993). However, the supply of white sugar (sucrose) to honey bee colonies can be a valuable management tool for beekeepers. ...
... There are several ways in which an association between infection and FA can be viewed (Alibert et al. 2002). Firstly, the metabolic costs of parasite infection may directly lead to developmental instability (Polak 1993). Alternatively, lower quality individ-uals that experience greater developmental instability may simply be more susceptible to infection (Møller 1996). ...
Fluctuating asymmetry (FA), defined as random deviations from perfect bilateral symmetry, is assumed to reflect developmental instability. FA is predicted to increase in response to environmental stress, including parasite infection. In addition, based on theory we predict a higher FA in sexually selected traits, due to their greater sensitivity to stress. We investigated the relationships between FA, parasitism and reproductive fitness in 2 species of gammarid crustacean, incorporating both sexual and non-sexual traits. We tested the hypothesis that gammarids infected by vertically transmitted Microsporidia will display higher levels of FA than those infected by horizontally transmitted trematodes, because vertically transmitted Microsporidia can be present at the earliest stages of host development. We found little evidence for a relationship between FA and fecundity in Gammarus spp.; however, the egg diameter for infected female Gammarus duebeni was significantly smaller compared to that for uninfected female G. duebeni. FA was not correlated with brood size in females or with sperm number in males. In contrast to our prediction, we report a lower relative FA in response to sexual traits than non-sexual traits. However, FA in sexual traits was found to be higher in males than females, supporting the theory that sexual selection leads to increased FA. Additionally, we report a negative correlation between FA and both trematode (Podocotyle atomon) and PCR-positive microsporidian (Nosema granulosis and Dictyocoela duebenum) infections and interpret these results in the context of the parasites’ transmission strategies. FA in G. duebeni and G. zaddachi appears to associate with trematode and microsporidian presence, although reproductive fitness is less altered by infection.
... Since, T. fuscum is widely distributed from Northern Scandinavia and Siberia to the Southern Europe (Löbl and Smetana 2010), it seems to be temperature-tolerant. Other ecological factors like food deprivation (Swaddle and Witter 1994, Nosil and Reimchen 2007, Szentgyörgyi et al. 2016) and parasitism rate (Polak 1993, Bonn et al. 1996 may also induce an increase in fluctuating asymmetry. Elevated asymmetry in the invasive T. fuscum population may be also caused by the cumulative effect of various environmental and/or genetic factors. ...
Biological invasions provide a unique opportunity to gain insight into basic biological processes occurring under new circumstances. During the process of establishment, exotic species are exposed to various stressors which may affect their development. Presence of the stressors is often detected by measurements of left-right body asymmetry, which consists of two main components: fluctuating asymmetry and directional asymmetry. Fluctuating asymmetry constitutes random differences between the two body sides, whereas directional asymmetry occurs when a particular trait is bigger on one of the sides. The relation between these two asymmetry components is still not fully understood. Our goal was to investigate the potential differences in asymmetry patterns between native and invasive populations of Tetropium fuscum (Fabr. 1787) (Coleoptera: Cerambycidae), a harmful forest pest native to Europe and introduced to North America. Wing asymmetry assessment was based on the geometric morphometrics of hind wings. We found that specimens from invaded area were markedly smaller and have more asymmetric wings than individuals from native population, suggesting some unfavorable conditions in the invaded area. Moreover, we found significant directional asymmetry in the native but not in the invasive population. On the other hand, differences between left and right hind wings were similar in the native and invasive populations, in terms of direction. This suggests that a high level of fluctuating asymmetry in the invasive population may blur the intrinsic directional asymmetry and hinder its detection. Our data show that fluctuating asymmetry has a potential as an indicator of developmental stress in invasive species.
... Whether or not short timescale fluctuating environments can function as a stochastic cue remains unknown, and this possibility has received little, if any, empirical attention. It may be argued that environmental influence on DI has been studied within the field of fluctuating or directional asymmetry (FA, DA; e.g., Polak, 1993;Hendrickx, Maelfait, & Lens, 2003;Moller, 2006), a commonly used measure of DI. These two measures of asymmetry are general descriptions of the degree of asymmetrical development in a bilateral character (Van Valen, 1962). ...
Diversified bet-hedging (DBH) by production of within-genotype phenotypic variance may evolve to maximize fitness in stochastic environments. Bet-hedging is generally associated with parental effects, but phenotypic variation may also develop throughout life via developmental instability (DI). This opens for the possibility of a within-generation mechanism creating DBH during the lifetime of individuals. If so, DI could in fact be a plastic trait itself; if a fluctuating environment indicates uncertainty about future conditions, sensing such fluctuations could trigger DI as a DBH response. However, this possibility has received little empirical attention. Here, we test whether fluctuating environments may elicit such a response in the clonally reproducing crustacean Daphnia magna. Specifically, we exposed genetically identical individuals to two environments of different thermal stability (stable vs. pronounced daily realistic temperature fluctuations) and tested for effects on DI in body mass and metabolic rate shortly before maturation. Furthermore, we also estimated the genetic variation in DI. Interestingly, fluctuating temperatures did not affect body mass, but metabolic rate decreased. We found no evidence for plasticity in DI in response to environmental fluctuations. The lack of plasticity was common to all genotypes, and for both traits studied. However, we found considerable evolvability for DI, which implies a general evolutionary potential for DBH under selection for increased phenotypic variance.
... Species collection information is provided for D. melanogaster, D. wassermani, D. nannoptera, D. pachea, and D. acanthoptera by Pitnick et aI. (1991); for D. nigrospiracula by Polak (1993); and for D. subpalustris, D. recens, D. guttifera, and D. putrida by Spicer and Jaenike (1996); D. arizonae was collected by T. A. Markow in San Carlos, Sonora, Mexico in May 1988. All remaining species examined were obtained from the National Drosophila Species Resource Center (Bowling Green State University, Bowling Green, OR); stock numbers are available from S. Pitnick upon request. ...
Females of all species belonging to the family Drosophilidae have two kinds of sperm-storage organs: paired spherical spermathecae and a single elongate tubular seminal receptacle. We examined 113 species belonging to the genus Drosophila and closely allied genera and describe variation in female sperm-storage organ use and morphology. The macroevolutionary pattern of organ dysfunction and morphological divergence suggests that ancestrally both kinds of organs stored sperm. Loss of use of the spermathecae has evolved at least 13 times; evolutionary regain of spermathecal function has rarely if ever occurred. Loss of use of the seminal receptacle has likely occurred only once; in this case, all descendant species possess unusually elaborate spermathecae. Data further indicate that the seminal receptacle is the primary sperm-storage organ in Drosophila. This organ exhibits a pattern of strong correlated evolution with the length of sperm. The evolution of multiple kinds of female sperm-storage organs and the rapidly divergent and correlated evolution of sperm and female reproductive tract morphology are discussed.
... They discovered that escape performance was negatively affected by the presence of Fluctuating Asymmetry, thus reducing the survival chances of asymmetric individuals. Polak (1993) performed an experiment on male Drosophila nigrospiracula to determine if parasites increase fluctuating asymmetry of the host. He purposely infected flies in the larval stage and also adults, to see if development stage was a factor in the appearance of asymmetry, while keeping a control group for comparison. ...
Morphometrics have had many uses in various fields of science. A modern trend of focusing on molecular data in biology might overlook the importance that morphometrics have had, and can have, in scientific experiments. The purpose of this paper is to illustrate the utility of geometric and linear morphometrics both in previous research and in a study we performed on four Zygaena carniolica (Scopoli, 1763) populations from Romania.
... However, the results of studies using FA as a measure of DI remain inconsistent. In insects, FA have increased under environmental stress factors such as temperature (Chapman & Goulson, 2000;Trotta et al., 2005, nutritional stress (Imasheva et al., 1999), parasitic infection (Polak, 1993) or chemicals (Abaga et al., 2011), as well as under genetic stress factors such as inbreeding (Carter et al., 2009), homozygosity (Messier & Mitton, 1996) or hybridization (Ross & Robertson, 1990). Nevertheless, some studies did not demonstrate considerable changes in the level of FA caused by environmental stress (e.g., nutritional stress, Vijendravarma et al., 2011;crowding, Chapman & Goulson, 2000;temperature, Jones et al., 2005) or genetic stress (e.g., inbreeding, Clarke et al., 1986;Fowler & Whitlock, 1994;Carter et al., 2009;hybridization, Smith et al., 1997). ...
Despite the fact that symmetry is common in nature, it is rarely perfect. Because there is a wide range of phenotypes which differs from the average one, the asymmetry should increase along with deviation. Therefore, the aim of this study was to assess the level of asymmetry in normal individuals as well as in phenodeviants categorized as minor or major based on abnormalities in forewing venation in honey bees. Shape fluctuating asymmetry (FA) was lower in normal individuals and minor phenodeviants compared with major phenodeviants, whereas the former two categories were comparable in drones. In workers and queens, there were not significant differences in FA shape between categories. FA size was significantly lower in normal individuals compared with major phenodeviant drones and higher compared with minor phenodeviant workers. In queens, there were no significant differences between categories. The correlation between FA shape and FA size was significantly positive in drones, and insignificant in workers and queens. Moreover, a considerable level of directional asymmetry was found as the right wing was constantly bigger than the left one. Surprisingly, normal individuals were significantly smaller than minor phenodeviants in queens and drones, and they were comparable with major phenodeviants in all castes. The correlation between wing size and wing asymmetry was negative, indicating that smaller individuals were more asymmetrical. The high proportion of phenodeviants in drones compared with workers and queens confirmed their large variability. Thus, the results of the present study showed that minor phenodeviants were not always intermediate as might have been expected.
... Two correlational studies, one involving D. nigrospiracula and the other involving western fence lizards (Sceloporus occidentalis), suggest that parasitism can cause FA in some cases. D. nigrospiracula found infected in nature with allantonematid nematodes had higher FA than either uninfected flies or flies burdened with mites (Polak, 1993). These results were predicted because nematodes infect fly larvae and are therefore more likely to disrupt development than mites which infest adult flies. ...
Fluctuating asymmetry is defined as the small, random deviations from perfect symmetry in a bilateral-paired trait. It arises from environmental and genetic stress occurring during ontogeny, and so, cannot be compensated readily in the adult form. Fluctuating asymmetry therefore can serve as a reliable indicator of individual phenotypic quality. Indeed, although there are exceptions, fluctuating asymmetry often is found to be correlated negatively with adult fitness components. In this chapter, the role of fluctuating asymmetry in sexual selection is reviewed. Of 23 animal taxa studied in this context, 65% exhibit a statistically significant positive association between morphological symmetry and estimated male mating success. Evidence suggests that female mate choice favors symmetrical males in barn swallows (Hirundo rustica), earwigs (Forficula auricularia), humans (Homo sapiens), scorpionflies (Panorpa japonica), and zebra finches (Taeniopygia guttata). But there is no consensus regarding why females prefer symmetrical males, nor about the evolutionary consequences of fluctuating-asymmetry-based sexual selection. It is proposed that parasites may provide a key to understanding these issues, because: (1) parasites are ubiquitous; (2) parasitism often is correlated positively with fluctuating asymmetry, either because it elevates fluctuating asymmetry, or because high fluctuating asymmetry hosts are immunologically deficient; and (3) parasite resistance is heritable in many host taxa. Thus, female choice in favor of low fluctuating asymmetry may reflect a preference for parasite-free males, because females potentially will be rewarded with (1) reduced probability of transmitting parasites to themselves and to offspring, (2) improved paternal care, and (3) transmission of resistance genes to offspring. Evidence showing that costs of resistance against parasites can be severe physiologically is also reviewed. It is shown that when resistant individuals incur such costs during ontogeny, they may exhibit greater fluctuating asymmetry as adults relative to their parasitized counterparts. It is suggested that expression of this pattern of fluctuating asymmetry variation across host types depends on the mode of parasite transmission, and this may explain why fluctuating asymmetry is actually positively correlated with fitness in certain host species.
... However, the evidence from experimental studies for such a role for FA is inconsistent. Some studies have detected an increase in FA under environmental stress (Parsons 1961(Parsons , 1962MÖller 1992;Polak 1993;Freebairn et al. 1996;Brake¢eld 1997;Hunt & Simmons 1997;Imasheva et al. 1997;Blankenhorn et al. 1998;Roy & Stanton 1999;Woods et al. 1999) while others have not (Beardmore 1960;Campbell & Emlen 1996;Arnqvist & Thornhill 1998;David et al. 1998;Hochwender & Fritz 1999). Where stress increases FA it usually does so in a trait-speci¢c way (MÖller 1992;Brake¢eld 1997;Hunt & Simmons 1997;Imasheva et al. 1997;Blankenhorn et al. 1998;Roy & Stanton 1999;Woods et al. 1999), but the FA of traits within an individual is generally uncorrelated (Clarke 1998;Woods et al. 1999), suggesting that FA is not a general indicator of organism-wide developmental stability. ...
... However, the evidence from experimental studies for such a role for FA is inconsistent. Some studies have detected an increase in FA under environmental stress (Parsons 1961(Parsons , 1962MÖller 1992;Polak 1993;Freebairn et al. 1996;Brake¢eld 1997;Hunt & Simmons 1997;Imasheva et al. 1997;Blankenhorn et al. 1998;Roy & Stanton 1999;Woods et al. 1999) while others have not (Beardmore 1960;Campbell & Emlen 1996;Arnqvist & Thornhill 1998;David et al. 1998;Hochwender & Fritz 1999). Where stress increases FA it usually does so in a trait-speci¢c way (MÖller 1992;Brake¢eld 1997;Hunt & Simmons 1997;Imasheva et al. 1997;Blankenhorn et al. 1998;Roy & Stanton 1999;Woods et al. 1999), but the FA of traits within an individual is generally uncorrelated (Clarke 1998;Woods et al. 1999), suggesting that FA is not a general indicator of organism-wide developmental stability. ...
The £uctuating asymmetry (FA) of bilateral traits is claimed to be a general indicator of environmental stress. Exaggerated sexual ornaments are thought to show elevated levels of FA and a greater response to stress than other traits. Previous work with stalk-eyed £ies (Cyrtodiopsis dalmanni) has shown that the FA of the sexual trait (male eye stalks), wing length and wing width were una¡ected by a continually applied food stress. Here we tested whether a transient stress (24-h heat shock at 31 8C during development) a¡ected the FA of these traits. A second experiment tested the combined stresses of transient heat shock at 31 8C with continuous exposure to desiccation. In each experiment, temperature shock reduced the trait size, con¢rming that the treatments were stressful. However, stress had no e¡ect on the FA of individual traits or the FA summed across all traits. Exposure to the combined stresses signi¢cantly elevated mortality and reduced trait size compared to the single-stress regime. However, FA did not di¡er signi¢-cantly between £ies from the two experiments. We found no evidence that FA in sexual and non-sexual traits re£ects transient stress during the development of C. dalmanni.
... Fluctuating asymmetry (FA), as a random deviation from perfect bilateral symmetry, has been widely used as a measure of environmental or genetic disturbance during development. There is considerable debate about the utility of FA as a measure of developmental stability (DS) (Whitlock, 1996;Van Dongen, 1998;Houle, 2000); since FA often increases with stress (Clarke, 1993;Badyaev et.al, 2000), including toxins and parasites (Clarke and McKenzie, 1987;Polak, 1993;Bjorksten et al., 2000 a), it is generally thought to be a reliable measure of DS, particularly when more than one trait is measured (Palmer and Strobeck, 2001). It has also been suggested that developmental stability is closely related to fitness through sexual or natural selection in general. ...
Due to the direct interaction between enzyme and substrate, the amylase system can provide valuable information on the relationship between homozygosity and developmental homeostasis under a changing environment in several Drosophila species, The adaptive significance of the relationship between genetic variability and environmental change manifests through the well-known polymorphism of the amylase locus (Amy). We examined the effect of gradual and abrupt changes in starch concentration in the nutritional substrate, on the developmental time, egg-to-adult viability and phenotypic plasticity in the progeny of Drosophila subobscura that was homozygous for "fast" (Amy(F)/Amy(F)) and "slow" (Amy(s)/Amy(s)) Amy alleles. Our findings show that gradual and abrupt nutritional changes exert a significant effect on developmental time and viability. A high heterogeneity among genotypes in fluctuating asymmetry (FA) and no direct association between FA and fitness components under the two experimental regimes of environmental change were observed.
... Several studies are consistent with the idea that episodes of parasitism during host development cause developmental instability both in animals (Møller, 1992;Polak, 1993;Folstad et al., 1996;Thomas et al., 1998) and humans (Alter, 1966;Kantor, 1994;Wright et al., 1972), and hence enhance FA. However, there are also several studies that fail to detect such a relationship (e.g. ...
... Fluctuating asymmetry (FA), a direct measure defined as a non-directional deviation from symmetry in bilateral traits, is related to stress (reviewed in Leung and Forbes, 1996). Therefore, FA could be analysed as a measure of parasite virulence (Allenbach, 2011) since parasites can cause direct stress on the host through metabolic costs (Møller, 1992;Polak, 1993). Thus, with an increase in parasite intensity and richness, FA would increase. ...
SUMMARY Most animals are concurrently infected with multiple parasites, and interactions among them may influence both disease dynamics and host fitness. However, the sublethal costs of parasite infections are difficult to measure and the effects of concomitant infections with multiple parasite species on individual physiology and fitness are poorly described for wild hosts. To understand the costs of co-infection, we investigated the relationships among 189 European eel (Anguilla anguilla) from Mar Menor, parasites (richness and intensity) and eel's 'health status' (fluctuant asymmetry, splenic somatic index and the scaled mass index) by partial least squares regression. We found a positive relationship with 44% of the health status variance explained by parasites. Contracaecum sp. (Nematoda: Anisakidae) was the strongest predictor variable (44·72%) followed by Bucephalus anguillae (Platyhelminthes: Bucephalidae), (29·26%), considered the two most relevant parasites in the analysis. Subsequently, 15·67 and 12·01% of the response variables block were explained by parasite richness and Deropristis inflata (Platyhelminthes: Deropristiidae), respectively. Thus, the presence of multiple parasitic exposures with little effect on condition, strongly suggests that eels from Mar Menor tolerate multiparasitism.
... However, not every trait shows an increase in fluctuating asymmetry with increased stress; different traits appear to be under different levels of stabilizing selection. Many morphological traits, especially those used in functions related to survival, are highly canalized and therefore are less susceptible to developmental disturbance (Polak, 1993). Other traits seem to be much more susceptible to stress. ...
The main aim of this study was to estimate phenotypic correlations among live weight, withers height, rump height, chest depth, chest width, thoracic girth, body length, hip widths (between iliac tuberosities and between ischial tuberosities) and forelimb cannon perimeter with antler length measured during the growth of marals on a Kazakh farm. The data comprised 18 animals studied during their growth (at 18 months and at 24 months). In maral, the first period of antler productivity takes place at the age of 24 months. This fact should be taken into account in order to select the best animals for antler production, which is the main purpose for farming this species.
... However, not every trait shows an increase in fluctuating asymmetry with increased stress; different traits appear to be under different levels of stabilizing selection. Many morphological traits, especially those used in functions related to survival, are highly canalized and therefore are less susceptible to developmental disturbance (Polak, 1993). Other traits seem to be much more susceptible to stress. ...
The objective of this study was to investigate asymmetry in antlers of Caspian Red Deer or maral (Cervus elaphus sibiricus) from two different genetic origins and maintained under similar conditions. Eighteen male Caspian Red Deer aged 24 months were studied. Nine animals belonged to the local Kazakh population and nine were directly imported Russian deer. The following data were obtained for right and left antlers: wet weight, stem length and circle and 1st, 2nd and 3rd shoot lengths. To obtain the values of antler asymmetries we used the absolute differences between the value of each trait on left and right sides. According to values of asymmetries obtained, the two populations neither showed differences from each other nor exhibited consistent directional trends in mean measures. Therefore, it could be concluded that Russian marals have adapted well to environmental conditions, presenting no different levels of environmental stress in relation to local Kazakh ones.
... Besides environmental stressors, other factors, such as a stress by parasitism, can cause a bilateral asymmetry on fish species (Leary & Allendorf 1989). parasites have been found to be associated with a deviance of symmetry in the development (Moller 1992, polak 1993, Reimchen 1997, Thomas et al. 1998, Brown & Brown 2002. This may be explained by (1) a direct stress caused by the metabolic cost of the parasite on its host (Moller 1992, polak 1993), (2) a variation of the abundance of the parasite related to stressful environmental conditions for hosts (Koskivaara & Valtonen 1992), or (3) a relationship between the genetic incapacity to interfere with developmental errors and the susceptibility to parasite (Moller 1996). ...
The parasite Anguillicola crassus threatening European eel since the eighties is regarded as a factor of stress. It is a very successful colonizer, and can severely impair swim bladder function. Glass eels were collected from the coastal lagoon Salses-Leucate of the Languedoc-Roussillon Region and were reared in experimental basins in which they were contaminated by several parasites. Otolith shape was examined to investigate to what extent parasitism affects otolith shape. Univariate and multivariate analyses of variance conducted on the otolith parameters of eels were realized in order to test the hypothesis that the parasite has an effect on these parameters and can generate a change in the shape of the ototiths. In this experimental approach, the otolith parameters varied according to the abundance of the parasite. The mean values of the size parameters and the Fourier coefficients displayed significant differences between right and left otolith. The values of the coefficient of shape, the circularity and the ellipticity of the otoliths were sensitive to the abundance of the adult parasite.
... Besides environmental stressors, other factors, such as a stress by parasitism, can cause a bilateral asymmetry on fish species (Leary & Allendorf 1989). parasites have been found to be associated with a deviance of symmetry in the development (Moller 1992, polak 1993, Reimchen 1997, Thomas et al. 1998, Brown & Brown 2002). This may be explained by (1) a direct stress caused by the metabolic cost of the parasite on its host (Moller 1992Moller , polak 1993), (2) a variation of the abundance of the parasite related to stressful environmental conditions for hosts (Koskivaara & Valtonen 1992), or (3) a relationship between the genetic incapacity to interfere with developmental errors and the susceptibility to parasite (Moller 1996). ...
... Elevated levels of FA have been found both in laboratory experiments and in natural populations of plants and animals exposed to different types of stressors [13][14][15]. In many species pollution [16][17][18], extreme temperatures [19,20], audiogenic stress [21], parasites [22][23][24], food deprivation [25,26] and high population density [27] can disrupt developmental stability and increase FA. Additionally, inbreeding [28,29], outbreeding [30] and hybridization [31] can also cause deviations from perfect symmetry. ...
The increase in human activities that leads to wildlife decline and species extinction poses an urgent need for simple indicators of environmental stress in animal populations. Several studies have suggested that fluctuating asymmetry (FA) can be an easy, direct measure of developmental instability because it is associated to environmental stress and, as such, it can be a useful indicator of population disturbance. We examined three different morphological traits in urban and rural populations of the common wall lizard (Podarcis muralis) to test whether anthropogenic disturbance causes an increase in FA. Compared to rural populations, urban ones showed higher levels of FA in all analyzed traits, thus providing evidence that FA can respond to anthropogenic disturbance. However, we also found significant differences in FA among traits, where femoral pores and subdigital lamellae, traits with a functional relevance, were more stable developmentally compared to supracilliar granules which have no evident function. Unsigned FA [abs(right-left)] exhibited significant, but weak, positive correlations among traits, indicating that developmental noise does not have a uniform effect across characters and thus questioning the view of developmental stability as an organism-wide property. The degree of signed FA (right-left) was more similar between structurally associated traits, possibly as an outcome of morphological integration. In conclusion, our results demonstrate that FA can be a reliable indicator of disturbance provided that it is analyzed on multiple traits simultaneously and examined at the population level.
... Zakharov et al. (1991) have shown that in some populations of the common shrew, Sorex, developmental stability is lowest when the local population density is the highest. Several authors (Polak, 1994;Escós et al., 1995a, b;Møller 1995b;Alados et al., 1996;Mara & Freeman, unpublished data) have shown that developmental stability declines as parasite loads or disease increases, provided that the parasitism occurs before the cessation of development. But in general, developmental stability has not been used to assess the impact of one species upon another. ...
Developmental instability has been used to monitor the well-being of natural populations exposed to physical, chemical and biological stressors. Here, we use developmental instability to assess the impact of grazing on Chryso-thamnus greenii and Seriphidium novum shrubs, and Oryzopsis hymenoides grass, common in the arid intermountain west of the U.S.A. Statistical noise in allometric relations was used as an indicator of developmental instability arising from grazing-induced stress. Unpalatable species that are not grazed (Chrysothamnus greenii) or species that are dormant during the winter–spring grazing period (Oryzopsis hymenoides) show lower allometric variability under high grazing pressure. Palatable species (Seriphidium novum) exhibit high developmental instability under low and high grazing pressure. Grazing pressure imposed by presumably co-adapted wild herbivores enhances developmental stability in species habituated to moderate grazing, like Oryzopsis hymenoides, but stresses plants such as Chrysothamnus greenii that prefer disturbed environments. These grazing effects are probably due to the impact grazing has on competitive relationships and not to the direct action of the herbivore on the plants.
... Thus, larger asymmetry values may not be indicative of higher stress or lower quality (Palmer and Strobeck 1992). While most researchers exclude skewed and platykurtic asymmetry distributions from analysis, leptokurtic asymmetry distributions are found and used commonly (e.g., Harvey and Walsh 1993, Polak 1993). One question is whether leptokurtic asymmetry distributions reflect genetic predispositions for asymmetry and thus should be avoided, or whether the developmental processes underlying true FA distributions (i.e., developmental noise and developmental stability) also might result in leptokurtic asymmetry distributions. ...
Fluctuating asymmetry (or FA) refers to directionally random deviations from bilateral symmetry for a character pair of an organism. Character FA has been related to stress imposed during development of organisms and quality or fitness of individuals. However, FA-stress and FA-quality relations often are absent or variable depending on the characters assessed. Some researchers have hypothesized that FA of sexually selected traits may relate to stress and fitness more reliably than other traits, and that genetic predispositions towards asymmetry may confound relations between asymmetry and either stress or quality. Others have suggested that because character FA is generated randomly, it may not relate to fitness or to FAs of other characters within samples of individuals. In this paper, we modelled development of character FA in relation to random developmental noise or perturbations, stress, developmental stability, and individual quality. We concluded that FA of sexually selected traits need not relate to stress or individual quality more than FA of other characters. We also determined that, in the absence of confounding factors such as genetic predispositions toward asymmetry, measurement error, and character FA-size relations, FA of some characters need not relate to stress or quality. Interestingly, leptokurtic asymmetry distributions could be generated using models expected to generate true FA; thus, leptokurtic asymmetry distributions should be assayed for relations with stress and fitness. We also found that unsigned FA could reliably relate to organism-wide developmental stability and quality, even in the absence of organism-wide FA relations among traits. Finally, conclusions about the utility of FA measures will depend strongly on representation of high FA individuals in samples, because FA-quality relations were typically triangular in distribution.
Males of some invertebrate species transfer large ejaculates, and many of the substances contained therein are incorporated by females into their somatic and ovarian tissues. These incorporated substances are expected to be energetically costly for males to produce, but benefit males by enhancing their fertilization success and/or the viability of their offspring. A better understanding of the evolution and maintenance of this important reproductive strategy should come from phylogenetic examination. We therefore quantified the extent of ejaculate incorporation by females of 34 species of Drosophila. Substantive amounts of male-derived proteins were more frequently detected in female somatic tissue than in ovarian tissue. Substantive ejaculate incorporation by females was found to have arisen numerous times across the phylogeny and tended to be lineage specific in expression. The extent to which evolution of a nutritive function of the ejaculate may have been influenced by phylogenetic history in the genus Drosophila is discussed. Macroevolutionary relationships between the amount of ejaculate incorporated by females and other features of species' reproductive and life-history biology, including body size, sperm length, the formation of an insemination reaction in females, and sex-specific ages of reproductive maturity, also were examined after controlling for phylogenetic effects.
We conducted a field study and a laboratory experiment to test whether ectoparasitic mites, Macrocheles subbadius, generate parasite-mediated sexual selection in the Sonoran desert endemic fruit fly, Drosophila nigrospiracula. Male flies gather on the outer surfaces of necrotic saguaro cacti where they engage in male-male competitive interactions and vigorous female-directed courtship. At these sites, operational sex ratios were significantly skewed toward males. The degree to which mites were aggregated among flies varied across the 25 fly populations sampled. The degree of mite aggregation across fly populations was strongly positively related to the mean number of mites per fly (intensity of infestation). Both the intensity and prevalence of infestation (fraction of flies infested) increased with the age of the cactus necrosis. Infested flies of both sexes were significantly less likely to be found in copula than uninfested flies, and mean intensity of infestation was significantly more pronounced in noncopulating than in copulating flies. The effect of attached mites on copulatory success exhibited dose-dependency, and this effect was more stringent in males: males or females with more than two and four mites, respectively, were never found in copula. The magnitude of parasite-mediated sexual selection was estimated for 12 fly populations by calculating selection differentials for each sex separately. The relation between intensity of infestation and magnitude of parasite-mediated sexual selection was stronger in males but significant for both sexes. We also assayed copulatory success of field-caught males in the laboratory, both during infestation and after experimental removal of mites. Males infested with two mites copulated less frequently than uninfested individuals, and in mating trials after mites had been removed, previously infested males copulated as many times as flies with no history of infestation. These findings, and the lack of difference in the number of mite-induced scars on copulating and single individuals in nature, strongly suggest that the reduced copulatory success of infested flies is attributable to an effect of mites per se, rather than to a character correlated with parasitism or previous parasite infestation.
Adaptive limits are considered in the context of the abiotic stresses to which organisms are normally exposed. For instance, nutritional stress is common in traditional human societies so that a dominant few survive and the remaining individuals in a population are vulnerable. In animals such channelling of resources can be achieved by complex territorial and social behaviour including sexual selection. Metabolic cost considerations underlie the susceptibility of carriers of sexual ornamental traits to stress from parasites, climate and inadequate nutrition. Individuals that develop the most extreme ornaments may have genes for stress resistance and may be relatively heterozygous. Similarly, genes for stress resistance appear to underlie survival to extreme ages; this leads to a stress theory of ageing. In the adjustment to natural environments, cultural factors can be a complication in human populations. However, in outlier Polynesian populations directly exposed to climatic stress, a body-heat balance analysis indicates that adaptation to extreme environments is a critical determinant of body form. Under these circumstances, genes for stress resistance would be advantageous, but the tradeoff would be reduced fitness in more benign environments.
The concept of an energy budget appears in Galton (1874) who appreciated the difficulty in applying such analyses to our own species. Here, the basic tenets of Darwin are considered under a more stressful scenario than is usually assumed. Connections between functional and evolutionary biology emerge from reductionism at this level as well as generalizations across disciplines. This follows from assuming that the target of selection of stress is at the level of energy carriers.
The past decade has seen a resurgence of interest in developmental instability, reflected in fluctuating asymmetry, as a concept in evolutionary ecology. Many investigations interpret fluctuating asymmetry in populations or subsets of populations as reflecting the existence of, or at least the potential for, natural or sexual selection. However, the biological and nonbiological factors underlying the appearance of developmental instability are not well understood. For example, the ability of heterozygosity vs genomic coadaptation to have an impact on development and cause fluctuating asymmetry is still debated, though each will have important, but different, implications for the genetic structure of populations and genetic architecture of various traits. These and other issues reviewed in this chapter must be clarified in order for the concept of developmental instability to be meaningful in evolutionary and ecological studies.
We conducted two pot experiments to examine the relationship between hemiparasitic plant (Rhinanthus serotinus. Scrophulariaceae) infection and host (Linum usitatissimum, Linaceae and Brassica rapa ssp. oleifera, Brassicaceae) performance. We were especially interested in the effects of hemiparasitism on the size and shape asymmetry of host flowers, since neither subject has been studied before. We also conducted a field experiment to examine the effects of shape asymmetry of B. rapa ssp. oleifera flowers on pollination success. The shape of flowers produced by both L. usitatissimum and B. rapa ssp. oleifera plants grown without parasites was less asymmetric, and for both host species, the flowers of plants grown without parasites had significantly longer petals than flowers produced by hosts with parasites. Significantly more bumblebees visited the inflorescences of B. rapa with untreated flowers compared to inflorescences with highly asymmetrical flowers (two of the four petals clipped shorter), whereas no difference was found in the number of visits made by syrphid flies. Parasitism significantly reduced host biomass and reproduction in both host species.
European eel parasites, in particular invasive species, are suspected to have a strong influence on the population dynamics of their host. The aim of this work was to study the relationship between parasitic fauna of yellow eels caught at Salses-Leucate lagoon and the fluctuating asymmetry (FA) of some functional bilateral traits: pectoral fins, eyes and otoliths. Epidemiological distance matrices and FA distance matrices were calculated on the basis of Euclidian distances between each pair of eel and were then compared wiht a Mantel test in order to establish if there was a relationship between parasitism and FA. Our results revealed different morphological characteristics between eels caught at different dates; only otoliths were found asymmetric. The parasite richness was of 10 species, 1 Nematoda, 1 Acantocephala, 1 Monogenea and 7 Digenea. We failed to find a significant relationship between asymmetry and parasitism, except fo parasites found in the stomach. We discussed the results in the light of the eel life cycle, the specificity of parasite-eel systems and the impact of parasites on the host physiology
The frequency of extra-pair paternity was studied in a population of Coal Tits Parus ater using DNA fingerprinting technique. High values were obtained: 15 of the 20 broods investigated (75%) contained at least one nestling sired by an extra-pair male and overall 40 of 158 nestlings (25.3%) were extra-pair young. Inter- and intraspecific comparisons revealed that breeding density cannot explain this high frequency of extra-pair paternity in Coal Tits.
Dutch elm disease is a phytopathogenic fungal disease transmitted by bark beetles, and it has eradicated elms from large parts of Europe and North America. I investigated phenotypic differences between diseased and healthy trees before and during infection, with special emphasis on measures of developmental instability of leaves (fluctuating asymmetry, frequency of phenodeviants) that may reflect adverse environmental and genetic conditions during foliar growth. I investigated whether stressed broad-leaved elm, Ulmus glabra, trees, as estimated from their leaf asymmetry and frequency of foliar phenodeviants, were more susceptible to the disease than trees with less asymmetric leaves. Trees that became diseased had larger leaf asymmetry than the nearest healthy neighbouring tree before acquisition of the disease. Foliar asymmetry was also caused by the disease since the degree of asymmetry increased from the first to the second year of infection. The frequency of elm leaves with abnormal morphology increased considerably from trees that were healthy to those that became diseased and particularly to the second year of the infection. Furthermore, the relative frequency of foliar side veins that joined veins from the other half of the leaf at the central vein decreased from healthy trees over susceptible trees that became infected to diseased trees. These results suggest that measures of developmental instability of elm leaves reflected susceptibility to Dutch elm disease as well as the negative effects of the disease on phenotypic development.
We conducted a field study and a laboratory experiment to test whether ectoparasitic mites, Macrocheles subbadius, generate parasite-mediated sexual selection in the Sonoran desert endemic fruit fly, Drosophila nigrospiracula. Male flies gather on the outer surfaces of necrotic saguaro cacti where they engage in male-male competitive interactions and vigorous female-directed courtship. At these sites, operational sex ratios were significantly skewed toward males. The degree to which mites were aggregated among flies varied across the 25 fly populations sampled. The degree of mite aggregation across fly populations was strongly positively related to the mean number of mites per fly (intensity of infestation). Both the intensity and prevalence of infestation (fraction of flies infested) increased with the age of the cactus necrosis. Infested flies of both sexes were significantly less likely to be found in copula than uninfested flies, and mean intensity of infestation was significantly more pronounced in noncopulating than in copulating flies. The effect of attached mites on copulatory success exhibited dose-dependency, and this effect was more stringent in males: males or females with more than two and four mites, respectively, were never found in copula. The magnitude of parasite-mediated sexual selection was estimated for 12 fly populations by calculating selection differentials for each sex separately. The relation between intensity of infestation and magnitude of parasitemediated sexual selection was stronger in males but significant for both sexes. We also assayed copulatory success of field-caught males in the laboratory, both during infestation and after experimental removal of mites. Males infested with two mites copulated less frequently than uninfested individuals, and in mating trials after mites had been removed, previously infested males copulated as many times as flies with no history of infestation. These findings, and the lack of difference in the number of mite-induced scars on copulating and single individuals in nature, strongly suggest that the reduced copulatory success of infested flies is attributable to an effect of mites per se, rather than to a character correlated with parasitism or previous parasite infestation.
A number of hypotheses have been proposed about the association between developmental stability, phenotypic variability, heritability, and environmental stress. Stress is often considered to increase both the asymmetry and phenotypic variability of bilateral traits, although this may depend on trait heritability. Empirical studies of such associations often yield inconsistent results. This may reflect the diversity of traits and conditions used or a low repeatability of any associations. To test for repeatable associations between these variables, multiply replicated experiments were undertaken on Drosophila melanogaster using a combination stress at the egg, larval, and adult stages of reduced protein, ethanol in the medium, and a cold shock. Both metric and meristic traits were measured and levels of heritable variation for each trait estimated by maximum likelihood and parent-offspring regression over three generations. Trait means were reduced by stress, whereas among-individual variation increased. Fluctuating asymmetry (FA) was increased by stress in some cases, but few comparisons were significant. Only one trait, orbital bristle, showed consistent increases in FA. Changes in trait means, trait phenotypic variability, and developmental stability as a result of stress were not correlated. Extreme phenotypes tended to have higher levels of FA, but only the results for orbital bristles were significant. All traits had low to intermediate heritabilities except orbital bristle, which showed no heritable variation. Only traits with low heritability and high levels of phenotypic variability may show consistent increases in FA under stress. Overall, the independence of phenotypic variability, plasticity, and the developmental stability of traits extend to changes in these measures under stressful conditions.
We evaluated the relationship between the intensity of parasites (the chewing lice Columbicola columbae and Campanulotes bidentatus, and the haematozoon Haemoproteus columbae) and the magnitude of fluctuating asymmetry (FA) of their Rock Pigeon Columba livia hosts. We measured the length of four morphological traits of 91 Rock Pigeons (both left and right sides) in Singapore between June and September 1996: wing, tail, tarsus and third digit. FA was either detected or assumed, after statistical correction, in the tail, tarsi and third digits of both sexes and in the wings of males. Correlations between parasite intensity (either ectoparasite or blood parasite) and FA in each measured trait were not significant (P > 0.15). We suggest that one of the possible reasons for the lack of a relationship between parasitism and FA in the Rock Pigeon is that the parasites studied may have little effect on the four host traits examined.
Numerous insects, including Drosophila nigrospiracula, that inhabit necrotic cacti of the Sonoran desert are host to Macrocheles subbadius, a cosmopolitan mesostigmatid mite. This paper shows that the mite pierces Drosophila integument and ingests haemolymph while attached to the abdomen of its host. Among field-caught flies, there was a strong negative relationship between mite load and wet mass of adult flies of both sexes. Thus, M. subbadius is an ectoparasite of D. nigrospiracula, contrary to the widespread belief that macrochelids form only phoretic associations with adult flies. The parasite harms its host in many ways. Under laboratory conditions, there was a significant negative effect of mite load on survivorship. In the field, there was a significant negative relationship between mite load and number of eggs carried by sexually mature females, suggesting that infested females resorb their oocytes to compensate for nutritional stress imposed by feeding mites. Likewise, in the laboratory, infestation lengthened somewhat the period prior to onset of oviposition, and decreased the number of eggs laid by females over their life. However, mite-infested females maintained on a yeast-supplemented diet overcame the potentially debilitating effects of mites, and were actually slightly, but not significantly, more fertile than uninfested females. Since the dietary conditions of flies influenced the degree to which fecundity was affected, the debilitating effect of mites is comparable to that of starvation. This conclusion derives support from the observation that laboratory females infested for 4 d, but whose mites were subsequently removed, produced fewer progeny than uninfested females. Although this effect was significant only among old females, it nevertheless indicates that the observed effects of mites on fecundity are not the result of mechanical constraints on oviposition behavior. Since intensities of infestation used in laboratory experiments were similar to those encountered in nature, observed ectoparasitic effects on fly fitness suggest that M. subbadius can reduce fly numbers in nature.
Associations between developmental stability, sexual selection, and viability selection were studied in the domestic fly Musca domestica (Diptera, Muscidae). Developmental stability of the wings and tibia of flies of both sexes, measured in terms of their level of fluctuating asymmetry, was positively associated with mating success in free ranging populations and in sexual selection experiments. Mated individuals may have obtained indirect fitness benefits from sexual selection of two different kinds. First, the entomopathogenic fungus Enthomophthora muscae (Zygomycetes, Entomophthorales) infects and kills adult domestic flies, and flies dead from fungus infections had more asymmetric wings than flies dead for other reasons. Experimental deposition of fungus spores on uninfected flies demonstrated that flies with asymmetric wings were more susceptible to fungus infections than flies with symmetric wings. Second, domestic flies were frequently eaten by insectivorous barn swallows Hirundo rustica, and flies depredated by birds had more asymmetric wings and tibia than surviving flies.
Developmental stability reflects the ability of a genotype to undergo stable development of a phenotype under given environmental conditions. Deviations from developmental stability arise from the disruptive effects of a wide range of environmental and genetic stresses, and such deviations are usually measured in terms of fluctuating asymmetry and phenodeviants. In this review, evidence is presented for a general relationship between health and developmental stability since the prevalence and the intensity of infections with parasites generally are associated with elevated developmental instability. The only exception is developmental stability in secondary sexual characters sometimes being positively associated with an increased frequency of venereal disease. Four studies have reported an elevated susceptibility to parasites among individuals with high levels of developmental instability. The cause of the positive relationships between parasitism and developmental instability may be either the generally poor condition of developmentally unstable individuals, or such individuals having genetically determined poor resistance to parasites as also reflected in an elevated level of developmental instability. The general relationship between parasitism and developmental instability has important implications for studies of parasite-host relationships in general and for conservation biology in particular.
1. Morphological characters of Salix borealis were monitored during 1994-96 at 10 sites along a transect crossing the heavily polluted surroundings of Severonikel smelter in NW Russia, and analysed with respect to pollution load and density of the principal herbivore, the leaf beetle Melasoma lapponica. 2. Leaf size and shoot growth increased and leaf pubescence decreased with an increase in pollution, whereas variation in other characteristics was not related to pollution load. 3. Leaf fluctuating asymmetry (FA) and leaf pubescence increased with an increase in herbivory, whereas variation in other characters was not related to foliar damage. 4. A field experiment demonstrated that leaf FA and pubescence were high in the year after defoliation. 5. The data on leaf FA, a non-specific stress indicator, suggest that for the extant individuals of S. borealis, defoliation resulted in detectable stress, whereas long-lasting severe pollution by sulphur dioxide and heavy metals caused no measurable stress response and may even stimulate growth of leaves and shoots. 6. Leaf FA of woody plants may serve as an early indicator of the biotic stress caused by herbivory, which expands the use of FA as a tool in helping to compare the relative strengths of different stressing agents.
Methodical problems concerning the practical use of fluctuating asymmetry level of bio-objects are considered. The questions connected with the variety of value asymmetry calculation methods and the use of asymmetry indicators efficiency and integrated indexes are discussed in detail. Discrepancy of research results when using several estimates of asymmetry is connected with their statistical properties and peculiarity of their normal variability which define sensitivity and operability of indicators. Concrete examples illustrating the negative influence of arithmetic transformations on the revealing properties of indicators are given: disturbance of normal distribution and the need of using rough nonparametric criteria , the increase of the importance of rare casual deviations, the introduction of additional variability components into an asymmetry level. Problems which arise in calculating asymmetry integrated indexes when signs unite with different levels of statistical parameters are separately considered. It is recommended to use the indicator of fluctuating asymmetry based on normalized deviation.
Recently, there has been much controversy over whether fluctuating asymmetry (FA) is related to stress during development, or to fitness of organisms following development. Many tests have found the predicted relations, whereas others have not. To account for these inconsistencies, some researchers have argued that FA of some traits (e.g., sexually selected traits) are more sensitive measures of stress, or are more strongly related to fitness, and that such relations will differ between poikilotherms and homeotherms. Using meta-analysis, we found that FA-stress and FA-fitness relations were nonspurious, despite the large number of relations tested. However, FA-stress and FA-fitness relations were fairly weak and highly heterogenous. Furthermore, our results suggested that trait type was not predictive of the presence or strength of FA-stress or FA-fitness relations and that relations were not stronger for poikilotherms, as one hypothesis suggested.
It is hypothesized that human faces judged to be attractive by people possess two features-averageness and symmetry-that promoted adaptive mate selection in human evolutionary history by way of production of offspring with parasite resistance. Facial composites made by combining individual faces are judged to be attractive, and more attractive than the majority of individual faces. The composites possess both symmetry and averageness of features. Facial averageness may reflect high individual protein heterozygosity and thus an array of proteins to which parasites must adapt. Heterozygosity may be an important defense of long-lived hosts against parasites when it occurs in portions of the genome that do not code for the essential features of complex adaptations. In this case heterozygosity can create a hostile microenvironment for parasites without disrupting adaptation. Facial bilateral symmetry is hypothesized to affect positive beauty judgments because symmetry is a certification of overall phenotypic quality and developmental health, which may be importantly influenced by parasites. Certain secondary sexual traits are influenced by testosterone, a hormone that reduces immunocompetence. Symmetry and size of the secondary sexual traits of the face (e.g., cheek bones) are expected to correlate positively and advertise immunocompetence honestly and therefore to affect positive beauty judgments. Facial attractiveness is predicted to correlate with attractive, nonfacial secondary sexual traits; other predictions from the view that parasite-driven selection led to the evolution of psychological adaptations of human beauty perception are discussed. The view that human physical attractiveness and judgments about human physical attractiveness evolved in the context of parasite-driven selection leads to the hypothesis that both adults and children have a species-typical adaptation to the problem of identifying and favoring healthy individuals and avoiding parasite-susceptible individuals. It is proposed that this adaptation guides human decisions about nepotism and reciprocity in relation to physical attractiveness.
Years of research on mating behavior have revealed that matings rarely occur at random between individuals in the same population. Why are some individuals more successful than others when competing for mates? What factors account for the particular combinations of types we observe in mating pairs? Current evolutionary theory explains mating patterns on the basis of maximization of fitness on the part of each sex and most species that have been investigated provide at least indirect support for this hypothesis. With Drosophila, it is possible to design controlled experiments that can answer directly questions about the relationship between mating behavior and fitness, and discover those factors that produce the nonrandom associations we observe.
The nematode Howardula aoronymphium (Allantonematidae) parasitizes several mushroom-feeding species of Drosophila of the quinaria and testacea species groups in eastern North America. The principal effect of nematodes on their hosts is a reduction in female fertility: females of Drosophila putrida and Drosophila testacea are sterilized by these parasites. The prevalence of parasitism varies substantially among host species and through time, showing evidence of seasonal as well as year-to-year variation. Because the principal effect of these parasites is on host reproduction and because they are not highly aggregated among hosts, this parasite-host system may be prone to unstable population dynamics. Some field evidence suggests that H. aoronymphium may influence the outcome of competition among its host species. Because these parasites and their hosts have similar population sizes, generation times. and rates of gene flow, they may interact evolutionarily in a dynamically interesting manner.
Fluctuating asymmetry (FA) is denned as small, random deviations from perfect bilateral symmetry in a bilaterally symmetrical
morphological trait. The relationship between FA in forewing length of males and the relative sexual attractiveness of their
pair-formation pheromones was studied experimentally in the Japanese scorpionfly, Panorpa japonica. This is the first study of the role of FA in pheromonal communication systems, and one of only a few studies on the relationship
between FA and sexual selection. Collectively, the results of four interrelated experiments reveal that females prefer the
pheromone of males of relatively low FA in forewing length. The experimental manipulation of forewing FA of males by cutting
wing lengths did not influence their olfactory attractiveness to females. In this case, females chose the male with the lowest
premanipulation FA. Thus, natural wing length FA apparently is correlated with inherent differences between males that influence
the properties of sex attractant males produce. Female preference for low-FA males may be adaptive as a result of material
and/or genetic benefits received by females.
Why do females prefer elaborate male mating displays in species where
they receive little more from males than their sperm? Here we review
three hypotheses for the evolution of mating preferences: direct
selection, the runaway process and the parasite mechanism. There is
growing support for direct selection, in which preferences evolve
because of their direct effects on female fitness rather than the
genetic effects on offspring resulting from mate choice.
Adaptive changes in reproductive effort (RE) of parasitized hosts may account for both inverse and positive relationships between host reproductive output and incidence or degree of parasitism. This hypothesis can be made more general (adaptive changes in patterns of allocation to reproductive functions), but has been largely ignored in the fields of behavioral and evolutionary ecology. In fact, definitive examples of such adaptive responses are lacking. Yet theory on life-history trade-offs predicts that hosts may minimize the impact of parasites by altering their own RE. Such alterations may occur with or without induction of defenses against parasites. Several empirical approaches exist for studying adaptive changes in host RE; all of these approaches require a firm understanding of the natural history of the parasite-host association under study. Tests of adaptive changes in host RE (and patterns of allocation) should provide a better understanding of parasite-host interactions and coevolution as well as insights into the evolution of adaptive phenotypic plasticity.
Mosquito control programs in California have relied on and still utilize a multitude of approaches for mosquito suppression. With the advent of DDT and other synthetic insecticides, new mosquito control programs were instituted encompassing many populated areas of the state. Within a few years, the most important culicine species, Aedes nigromaculis, became resistant to DDT in California. Another important and widespread species, Culex tarsalis Coquillett, also showed resistance to a number of mosquito larvicides. As more mosquito control programs were initiated after the World War I, the use of larvicidal oils also attracted greater attention. The second material to be developed for mosquito control was Paris green. Among the chemical control agents, the petroleum hydrocarbon larvicides played a dominant role up to the time of the advent of DDT and other synthetic organochlorine insecticides. Dimilin, a chitin synthesis inhibitor, has been extensively studied against mosquitoes, and it is expected that this material will become commercial in the near future.
This chapter reviews the recent development of housefly resistance on Danish farms. The trials of fly control and investigations of resistance on farms during 1973–1975 were concentrated on pyrethroid aerosols or space sprays with the purpose of investigating the possibility of fly control by frequent treatments, the potential of developing resistance to pyrethroid formulations, and the persistence of dimethoate and other Organophosphorus compounds (OP) resistance when OP pressure was relaxed. In 1973, fly-infested stables on 23 trial farms were treated frequently (twice a week) during the whole fly season with pyrethroid space sprays. In 1973 and1975, dimethoate-resistance was monitored on most of the trial farms. The present multi-resistance in Danish houseflies is the result of the sequential selection pressures by many compounds which have accumulated and combined several resistance factors.
This experiment concerns with the selection of a silkworm resistant to virus induction. Larvae of a silkworm strain were reared as usual, except for treatment by refrigeration at 5°C for first 24 hours after the ecdysis of the 2nd, 3rd, 4th and 5th instar, respectively, and eggs were obtained from the survived moths. The diseases appearing by this treatment were nuclear and cytoplasmic polyhedroses and flacherie. This treatment was performed through 13 generations, and in the 11th to 13th generation one batch rearing was made. Survival rate of a selected strain from these generations was always higher than that of the original (non-selected) strain and the resistance to virus induction by means of cold treatment was recognized. Subsequently, the effect of malnutrition was compared with selected and non-selected strains. The larvae were reared on harder mulberry leaves during the 1st and 3rd instars and on rotten leaves during the 4th and 5th instars. In the common strain C 115 × J 122 all larvae died by the 5th instar and in the non-selected strain 4 out of 413 larvae pupated, but eventually died, while in the selected strain 130 out of 325 larvae became adult. From this result, it was considered that the selected strain by means of cold treatment was resistant to virus induction by malnutrition. Since the selection has been performed under condition of mass-rearing, a question arises whether the larvae of selected strain will be reinfected with the infectious virus from outside, by which a lysogenization-like phenomenon will be caused. For this purpose, the nuclear polyhedrosis virus was injected into the silkworm pupae and the eggs laid by the heavily infected moths were obtained. Even with such eggs, it was not possible to find out distinct difference in the induction rate by the exposure to cold treatment or at normal rearing between virus-injected and non-injected batches, and it was considered that a lysogenization-like phenomenon would not appear. The resistance to virus infection was examined employing the selected strain by means of cold treatment, non-selected strain and other silkworm strains. The difference in the susceptibility (log LD50) for the nuclear polyhedrosis virus was not remarkable among them, and thus the resistance to virus induction seems to be independent from that to virus infection. © 1961, The Japanese Society of Sericultural Science. All rights reserved.
Fluctuating asymmetry (FA) is a widely used measure of developmental stability. Differences in FA indexes among samples are usually interpreted as reflecting differences in the level of developmental stability. If developmental stability is the ability to correct for small, random developmental perturbations of exclusively environmental origin, then a distribution of right-minus left (R-L) which may include both genetically and environmentally caused asymmetries, may not be a good measure of developmental stability, R-L distributions that depart significantly from the statistical criteria for ideal FA (mean of zero, normal distribution) are unsuitable as descriptors of developmental stability because a fraction of the asymmetry variation may have a genetic basis. In addition, broad-peaked or bimodal (platykurtic) distributions of R-L, which reveal the presence of antisymmetry, also imply genetically based asymmetries and thus seem inappropriate as descriptors of developmental stability. Finally, both skewed distributions and narrow-peaked, long-tailed (leptokurtic) distributions may arise in mixed samples composed of two or more groups of individuals where each exhibits a different form of asymmetry and where one or more forms of asymmetry may have a genetic basis. -from Authors
Presents the results of a comparative study of haematozoa of tropical Central and South American birds and discusses the value of such studies for critically evaluating the Hamilton and Zuk hypothesis. The tropical data set allowed the study of a much larger sample (526 species) than had previously been examined, and one containing many of the gaudy birds found in tropical habitats. Use of tropical birds allowed comparison between migrant and resident species; because the Hamilton-Zuk hypothesis requires that parasites coevolve closely with their hosts, resident species should show the relationship between brightness and parasite level more strongly than migrant species, which are more likely to be exposed to different sets of haematozoa in wintering and breeding habitats. The confounding effect of phylogeny must be dealt with, ie certain groups of species may show the association between brightness and infection level merely because of shared ancestry. -from Author
1. A technique for sterilizing large numbers of Drosophila eggs is described. This gives about 95% successful cultures.
2. Using this method, dose-response curves have been obtained for all the main dietary constituents under conditions in which interactions between them are likely to be of little significance. Responses to the following are detailed: casein, fructose, cholesterol, lecithin, RNA, thiamine, riboflavine, nicotinic acid, pantothenic acid, biotin, pyridoxine, folic acid, choline and a water-soluble fraction of yeast which improves growth.
3. Other substances which have been included in Drosophila media are shown to have no value for the inbred strain of flies tested.
4. It is also shown that only K, P, Mg and Na salts need to be included in the food.
5. On the basis of these findings an optimal medium is formulated which allows larval development to be completed in about 4.4 days. This compares with 4.1 days when the same strain is reared on an optimal supply of killed yeast.
6. The minimal nutritional requirements of Drosophila larvae are shown to be considerably less than those of other aseptically cultured insects and, as far as the vitamins are concerned, only broadly related to the amounts found in yeast. The possible reasons for this are discussed.
1. The numbers of right-handed and left-handed males of Uca lactea were nearly equal, and no significant regional or yearly differences from the ratio of 1:1 were found.2. In the early stages of growth, all the crabs had two small chelipeds, and no morphological differences were found between the sexes. All males with a carapace width greater than 5.3 mm exhibited cheliped asymmetry. Apparently, a male normally loses one of his chelipeds which then regenerates into a small cheliped; the remaining cheliped develops into a giant, and the male attains his cheliped asymmetry.3. Artificial removal of one cheliped from megalopae and young crabs whose chelipeds were still in the symmetrical condition induced handedness. The large cheliped always developed on the intact side.4. When males suffered the simultaneous removal of both chelipeds in their megalopa or crab stage before the attainment of asymmetry, they could not develop a giant cheliped but instead kept two small chelipeds permanently. However, no abnorm...
We examined the association between heterozygosity at 42 enzyme loci and fluctuating asymmetry at five bilateral meristic characters in 14 population samples of rainbow trout, cutthroat trout, and brook trout. There is a significant negative correlation between heterozygosity and the proportion of asymmetric characters per individual in two populations of rainbow trout and two populations of cutthroat trout. This correlation is negative in 13 of the 14 population samples (sign test, P < .001). Thus, individuals that are more heterozygous at isozyme loci have reduced fluctuating asymmetry; this appears to be general among salmonid fishes. We also found that individuals with obvious morphological deformities in three populations have increased fluctuating asymmetry. Thus, fluctuating asymmetry appears to be a reliable indicator of overall developmental stability and is therefore negatively correlated with fitness. The association between heterozygosity and asymmetry and between asymmetry and morphological d...
Dispersal of Drosophila nigrospiracula on naturally occurring necrotic saguaro cacti occurs at rates up to three times higher than those observed for any other Drosophila. In eight separate experiments, a total of 3,034 marked flies were captured at 22 cacti. Overall immigration rates averaged 6.83 percent over 371 m. Immigration from a single cohort averaged 3.67 percent overall distances. Effective-population sizes at a single cacti are estimated from 361 to 3,999, while the overall population of D. nigrospiracula is estimated at 100 billion flies. The genetics of large, mobile populations has been considered, using island, stepping-stone, and isolation-by-distance models. All three models suggest that D. nigrospiracula is so mobile that drift plays a minor role. The population acts as if it were panmictic. This view is supported further by behavioral considerations. Immigrants are an effective part of mating populations. Barriers to dispersal are nonexistent. Adverse habitat conditions increase dispersal rates. Three explanations are proposed for the high dispersal rates of D. nigrospiracula. First, immature adults may be more mobile than mature flies. Second, dispersal may be increased by food stress. If so, baited studies, which considerably enrich the environment, underestimate dispersal rates in adverse environments. Third, dispersal rates are an evolutionary response to habitat predictability. Those species (such as D. nigrospiracula at cacti) which occupy short-lived and widely-spaced habitats are more mobile than species (such as D. melanogaster at a garbage dump) which occupy a small, rich, constantly renewed habitat.
Fluctuating asymmetry is an epigenetic measure of the ability of
individuals to undergo identical development of a usually bilaterally
symmetrical character on both sides of the body. Horns of beetles and
spurs of birds are elaborate structures usually restricted to or
enlarged in individuals of the limited sex and frequently used in
intrasexual combat. Individuals with large horns usually win fights
against individuals with small horns which suggests that horn size may
reliably signal male fighting ability. A comparative study of the
patterns of fluctuating asymmetry in horns of beetles and spurs of birds
showed that the degree of asymmetry in these secondary sex traits was
considerably larger than in elytra and wing length, which are apparently
not subjected to sexual selection. There was a negative relationship
between the degree of asymmetry and size of the secondary sex trait
while the relationship for elytra and wing length was flat or U-shaped.
This demonstrates that horn and spur size may reliably reflect male
quality as determined by the degree of fluctuating asymmetry.
Extravagant secondary sexual characters, i.e. sexual ornaments, are exaggerated, often bilaterally symmetrical traits of great intricacy of design. The full expression of such traits is likely to be very costly and close to the limits of production. Any kind of environmental stress is therefore more likely to affect the expression of ornaments than that of any other morphological trait not subjected to strong directional selection. One measure of the ability of individuals to produce extravagant sexual traits is their degree of fluctuating asymmetry. This occurs when symmetry is the normal state and there is no tendency for the trait on one side of the body to have larger character values than that on the other. The degree of fluctuating asymmetry has been shown to reflect the ability of individuals to cope with a wide array of environmental stress (review in Parsons (1990)). We predicted that sexual ornaments should show a larger degree of fluctuating asymmetry than other morphological traits or than homologous traits in non-ornamented species. If ornaments honestly indicate the quality of individuals, high quality individuals should develop little asymmetry and large traits. Thus, we predicted a general negative relation between the degree of asymmetry and the size of ornaments. This should not be the case for other traits or for homologous traits in conspecific females or in either sex of monomorphic species. We tested these predictions on elaborate feather ornaments in birds, as these have been shown to be used as cues during female choice. We made pairwise comparisons between males and females of ornamented species and between males of ornamented and of non-ornamented, confamilial species. Sexual ornaments showed both a larger absolute and relative degree of fluctuating asymmetry than did wing length or did traits homologous to the feather ornament in females and in males of non-ornamented species. The degree of fluctuating asymmetry for tail ornaments generally showed a negative relation with the size of the ornament, whereas that was not the case for wing length or for traits homologous to the feather ornament in females and in males of non-ornamented species. The large degree of fluctuating asymmetry in ornaments and the negative relation between ornament size and degree of asymmetry suggest that fluctuating asymmetry in ornaments reliably reflects male phenotypic quality.
A negative correlation between asymmetry (as measured by the dissimilarity of bilateral structures within individuals) and heterozygosity is reported for 15 populations of lizards. Asymmetry is assumed to measure developmental instability. If future studies verify this result, we will be led to conclude that individuals from relatively heterozygous populations are fitter by this criterion than are individuals from relatively homozygous populations. Due to the inherent 'noise' in studies of this type, it is recommended that workers maximize the range of heterozygosities among the sampled populations.
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We infected male guppies Poecilia reticulata with a naturally occurring monogenean parasite, Gyrodactylus turnbulli, in order to examine effects of parasitism on the expression of color patterns and on attractiveness to females. The color of carotenoid spots and ability to attract females were compared between experimentally infected fish and a control group of their fullsib brothers, which had identical color patterns and were treated identically except for actual exposure to parasites. The orange spots of males that had been infected for 9 days followed by treatment with medication to remove parasites became significandy paler and less saturated. Control males (also treated widi medication) showed no significant changes in their orange spots. Females in a divided aquarium choice-apparatus showed no preference between control and infection-treatment males initially, but showed significant discrimination after the infectiondisinfection treatment. Females spent less time near males that had been infected and responded to a smaller fraction of their courtship displays relative to control males. There were slight differences in courting rates of males between treatments. Parasitic infection appears to reduce the degree of expression of carotenoid colors in guppies, and females are able to discriminate against recently infected males, probably on the basis of the color change. By avoiding infected males, females may be able to avoid becoming infected themselves, or they may be able to identify mates based on "good genes" for parasite resistance diat can be passed on to their offspring.
A new pattern in the variation of morphological characters, described in insects, birds and mammals, depends for its detection on distinguishing among 3 operational levels of variation: 1) within-individual variation in paired or homologous, segmental structures (asymmetry of bilateral organs or traits); 2) within-population variation of a trait, usually estimated by the standard deviation or coefficient of variation (CV); 3) differences in variability between different traits. The IG-OG effect (increased asymmetry in extreme phenotypes) is apparently most strongly expressed in the least variable traits (level 3), those with CVs of 2.5 or less. When the frequency distribution of such a character, and the amount of within-individual (asymmetry) variation is compared among them, it was found that OG individuals were more asymmetrical than IG individuals. This is the same as discovering a correlation between asymmetry and absolute distance from the mean. The IG-OG effect was predicted from a general theory of morphometric variation. The theory, allomeric variation, assumes that, within a set of homologous or nested characters, the contribution of developmental noise (random molecular motion and interactions) to the variability of characters decreases as the size of the characters increases. If it is assumed that developmental stability is correlated with the degree of genotypic heterozygosity, then OG individuals will be less stable than IG individuals. -from Authors
Allomeric variation is the tendency for variability in morphological traits to decrease as the size (number of parts) increases. Such a trend is supported by the commonly observed correlation between the CV and size of anatomically similar traits. The mechanistic basis for allomery is probably the decreasing contribution to variation of random events or noise as the number of parts increases. The principle of allomery is elaborated and an attempt is made to integrate it with observations from the literature on stress physiology and developmental genetics. The physical-chemical basis of phenotypic randomness (noise) is explored and a theory is proposed that associates noise with random molecular motion. One of the genetic corollaries of this explanation for allomery is the possibility that the random contribution to the variance of traits should decrease and the additive genetic component should increase in a series of similar traits ranked in order of decreasing CV. Another consequence of the theory should be the phenotypic partitioning of relatively homozygous and heterozygous genotypes as CV decreases; homozygotes should occur with greater frequency in the tails of phenotypic distributions, while heterozygotes should occur near the mean witn increasing frequency. Some of the predictions that follow from this theory are discussed. -from Author
Given that extravagant secondary sexual characters, i.e. ornaments, give
males a mating advantage through male-male competition or female choice,
all males should benefit from growing very large ornaments. If sexual
characters are to function as reliable advertisements of male quality,
there must be a limit for males in their ability to grow or maintain
large ornaments because of associated fitness costs, which may be more
prominent in low than in high quality individuals. I used fluctuating
asymmetry in ornament size as a measure of the ability of individuals to
achieve identical development of the ornament on both sides of their
body. Long-tailed males of the sexually size dimorphic swallow Hirundo
rustica had less asymmetrical tails than had shorter-tailed individuals.
The cost of fluctuating asymmetry in tail size in terms of
manoeuvrability during flight was estimated directly by manipulating the
degree of asymmetry and thereafter recording the number of times
swallows hit semi-partitions in a flight cage. Both the degree of
asymmetry caused by experimental treatment as well as the natural degree
of asymmetry negatively affected manoeuvrability during flight,
suggesting that asymmetry per se and inherent differences between
individuals affected their flight performance. Female mate choice may be
optimized by relying on fluctuating asymmetry in male ornaments, such as
the tails of male swallows, being likely to reflect individual
properties of direct fitness value.
A mathematical model is developed that examines the potential for the origin of a female mating preference directed at a quantitative character in males. The criterion character is assumed to be equally expressed in both sexes, subject to optimizing natural selection, and unrelated to any direct contribution males may make to their progeny. I derive an expression for the conditions under which alleles for a mating preference can increase, when rare, in an initially randomly-mating population, as a result of increased viability among the offspring of discriminating females. The magnitude of the increase in offspring viability owing to female choice increases with increasing heritability of the selected character and with increasing discrimination by females against males deviating from the optimal mate type. Characters under very weak or very strong selection show less potential to become objects of a mating preference than do characters under selection of intermediate strength. Only stabilizing preferences for phenotypically optimal males can originate in equilibrium populations, and the potential for their evolution, while present, is small. In nonequilibrium populations, directional preferences for males that exceed the phenotypic optimum are favored, and the potential for their evolution can be very large. Since directional preferences are more likely to produce unstable evolution than are preferences toward the mean of the population, it is suggested that the evolutionary history of male traits may strongly influence the nature of sexual selection on them.
One of the more difficult tasks in evaluating the possible deleterious effects of multiple toxicants on natural communities is in defining subtle sublethal effects before the onset of chronic morbidity. We reason that before detectable changes in either species diversity or species abundance occur subtle changes must take place in a number of important processes, ranging from molecular to behavioral changes. Unfortunately, changes in these parameters have proven most difficult to detect with current methodology. We, therefore, have been examining the possible use of fluctuating asymmetry as a possible measure of environmental stress. Fluctuating asymmetry is simply the random deviation from perfect symmetry of any bilateral anatomical character. It is, therefore, a nonspecific measure of developmental perturbation. Using asymmetry analysis on three species of marine teleost-barred sand bass, Paralabrax Ilebulifer; grunion, Leureslhes lenuis; and barred surfperch, AlIlphistichus argellteus-from southern California and B
The correlations between the fluctuating asymmetries of different characters were investigated in three species (chaetae and wings of Drosophila melanogaster, cheek teeth of Peromyscus leucopus, and cheek teeth of the fossil horse Griphippus gratus). A mean correlation of 0 was found for the two former species, but a mean positive correlation of +0.046 was found for the horse. Reasons are given why this exception may be only apparent. The intensities of some morphological differences in Drosophila have a general component even though they may be bilaterally independent. The lack of variation for a general buffering capacity against minor developmental accidents was not expected. This and related matters are discussed.
The mosquito Culex pipiens quinquefasciatus Say was found to have developed resistance to the mermithid nematode Romanomermis culicivorax Ross and Smith after some 300 generations. Parasitism was 32-42% higher in a native strain than in the laboratory strain of the host under similar conditions. Differences were even greater when the number of successful penetrations (multiple parasitism) was measured. No evidence of humoral defense mechanisms were found, and the mode of resistance has not been determined.
Maynard Smith et al.1 have recently suggested that newly evolved phenotypes will be more variable than long-established ones when developmental constraints have evolved
through canalizing selection in which similar phenotypic expression is stabilized across a range of genotypes2. There is as yet little evidence for this1,3. Fluctuating
asymmetry1 (random differences between left and right sides of a normally bilaterally symmetric organism) has been used to indicate developmental stability and to define environmental
or genetic stresses on development4–14. Here we show that insecticide-resistant phenotypes of the Australian sheep blowfly, Lucilia cuprina, show greater fluctuating
asymmetry than susceptible phenotypes when resistance first evolves, and that continued use of an insecticide after resistance develops leads to a return in the asymmetry of resistant phenotypes to
the level of susceptibles. The asymmetry of resistant phenotypes increases during repeated back-crossing to a susceptible strain, suggesting that developmental stability may be modified by
selection.
IT was shown several decades ago that the reduction in genetic heterozygosity produced by inbreeding in domesticated plants and animals is accompanied by an increase in morphological variability1,2. While studies of laboratory populations and results of plant and animal breeding have been instrumental in identifying the relationship between genetic heterozygosity and morphological variability, such investigations often involved substantial changes in genetic heterozygosity, such as are produced when entire chromosomes are made homozygous. For this reason their relevance to the levels of heterozygosity in natural populations is unclear. Until recently attempts to examine this relationship in natural populations were hindered by the inability to routinely estimate levels of genetic heterozygosity in nature. However, determinations of genetic heterozygosity at specific enzyme-loci can now be made by electrophoresis. Recently Mitton3 found that heterozygotes for a set of five enzyme-loci had reduced multivariate variances for a set of morphological characters when compared to homozygotes at the same loci in populations of the killifish, Fundulus heteroclitus. It is very important to determine the generality of this observation for other species populations. I have now examined the relationship between genetic heterozygosity, as identified by electrophoresis, and the variance of morphological characters in the monarch butterfly, Danaus plexippus. Study of six polymorphic enzyme-loci in the monarch shows that once again heterozygotes have smaller variances for morphological characters when compared to homozygotes at the same locus.
Measurements of tail and wing length in swallows suggest that length in males was a reliable advertisement of male quality. Since females use tail length as a cue during mate choice, they will prefer males with symmetrical tails, who have proven their ability to pay the costs of producing the most costly ornament. Fluctuating asymmetry in secondary sexual traits may signal the ability of males to cope with environmental conditions during growth and development of the ornament. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
1. Published data suggest that mean left-right asymmetry in number of sternopleural bristles of D. melanogaster declines when inbred lines are crossed, while the corresponding variance for sternite bristles remains unchanged. Some genetic tests were undertaken to analyse this difference in behaviour of the two characters.
2. A progeny test on a wild stock showed that a small amount of genetic variance in sternopleural asymmetry was present, equivalent to about 2% of the total phenotypic variance.
3. It was possible to increase and decrease the level of sternopleural asymmetry in two wild stocks by selection. These experiments gave an estimated heritability of some 2–3%, in close agreement with the progeny test. Change in asymmetry did not necessarily lead to a change in mean count.
4. Homozygous lines, consisting of individual third chromosomes from the Renfrew wild stock made homozygous in an inbred line genetic background, were intercrossed, and the average indices for a number of characters of eight inter crosses involving eight lines were compared with their mid-parent averages. Thorax length was 2% greater and its variance 32% less in the crosses; total sternopleural count and its variance did not change significantly, but the asymmetry variance declined by 18%. In contrast, the corresponding asymmetry or independent variance for numbers of sternite bristles was 6% higher in the crosses, although the total sternite count and its variance did not change. These results fit in with previous work.
5. Tests on a similar set of homozygous lines in which the third chromosomes came from the SP wild stock, and on some long inbred lines from the Pacific wild stock, gave discordant results. Of eight SP lines examined, four were homozygous for a gene polychaetoid , and four were homozygous for a genetic effect causing sockets without bristles to occur among the sternopleurals. Both types had much greater sternopleural variance and asymmetry than the Renfrew lines, and both indices declined sharply in intercrosses leaving these genetic effects heterozygous, but neither declined if they were left homozygous in the crosses. Similarly high sternopleural variances were found in the Pacific lines, but only the total variance declined in males and only the asymmetry variance declined in the females, when they were intercrossed. All the four Pacific lines tested appeared to be homozygous for a genetic effect which caused a variable number of dorso-central and scutellar bristles to be replaced by sockets without bristles, and an occasional extra scutellar bristle to appear. This effect was also probably responsible for the high sternopleural variances.
6. Males of the Pacific inbred lines and intercrosses were compared when reared on the normal live medium and on a synthetic diet in reduced concentration, which reduced body-size by 23% (thorax area). The inbred lines were reduced more than the F 1 's in total sternopleural count and its variance, but the F 1 's were reduced more in sternopleural asymmetry, by the restricted diet.
7. The problems of interpreting these experiments, in view of our ignorance of the biological functions and attributes of the sternopleural and sternite bristles, are discussed. It is concluded that we have no basis yet for deciding whether sternopleural bristle number is of adaptive significance, but this is considered improbable.
8. The experimental evidence suggests that sternopleural asymmetry cannot be considered a measure of general developmental stability, particularly as the level of asymmetry can be reduced by selection well below that of typical wild stocks.
9. The scaling problems arising when the mean asymmetry of lines with different mean counts are to be compared, are examined, and it is suggested that the ratio of asymmetry to total count does not eliminate scale effects.
10. Developmental and anatomical differences between the sternopleural and sternite bristles suggest a possible reason why they behave differently when inbred lines are intercrossed.
Darwin1 proposed that secondary sexual characters, such as
the long tails and bright plumage of many birds, evolved because females
use them as cues in male choice. The question of why females should
prefer males with such apparently deleterious characters is currently
the subject of vigorous debate2-7. Hamilton and
Zuk8 suggest that females use secondary sexual characters to
assess a male's ability to resist parasites. A prediction of this
hypothesis is that male brightness should correlate positively with
parasite load across species, and the only evidence advanced in support
of the model is Hamilton and Zuk's8 finding that such a
correlation exists across North American passerines. But interspecific
correlations of this sort can result from phylogenetic associations
through common descent or from independent associations with some
confounding variable, such as an aspect of behaviour or
ecology9-13. Here, I use data on European passerines and an
enlarged data set on North American passerines to demonstrate positive
relationships between male brightness and parasite prevalence which
remain when the effects of taxonomic, behavioural and ecological
variables are removed.