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Developmental instability is heritable
... But this level of heritability is precisely the same as that found for comparable estimates made for the mandibular characters in mice used in the QTL study (Leamy et al., 1997) as well as eight quasi-continuous skeletal characters in these random-bred mice (Leamy, 1997b). In contrast, Moller & Thornhill (1977b) calculated a heritability of FA for several characters in six different asymmetry studies that averaged 0.16 and was statistically signi®cant. These studies were chosen because all tested for the presence of DA and antisymmetry and had acceptably low measurement error in the characters used (Moller & Thornhill, 1977b). ...
... In contrast, Moller & Thornhill (1977b) calculated a heritability of FA for several characters in six different asymmetry studies that averaged 0.16 and was statistically signi®cant. These studies were chosen because all tested for the presence of DA and antisymmetry and had acceptably low measurement error in the characters used (Moller & Thornhill, 1977b). But the generality of this result is compromised by the fact that four of these studies appear to be unpublished and not readily available for analysis. ...
In bilateral characters, two kinds of asymmetries are common: fluctuating asymmetry (FA), or nondirectional variation between left and right sides, and directional asymmetry (DA), in which one side is consistently larger than the other. FA has been extensively used as a measure of developmental stability because of its presumed environmental basis whereas DA has not typically been recommended because it has been presumed to have at least some genetic basis. To test these two hypotheses, heritabilities were calculated via parent–offspring regression for both DA and FA in 10 triply measured mandible characters in random-bred mice. Midparent estimates of heritabilities of DA in the 10 characters were quite low (mean = 0.06), but significant for one character as well as the sum of the DA values over all characters (0.21). Midparent estimates of heritability of FA in the 10 characters also were low (mean = 0.03), but not significant for any individual character or the sum of the FA values over all characters. Heritabilities of developmental stability calculated from heritabilities and repeatabilities of FA in the mandible characters were higher in magnitude (mean of midparent estimates = 0.45), but all still were not statistically significant. It was concluded that both hypotheses were supported, but that genetic variation in DA was so small that the potential for DA as an indicator of developmental stability should be explored.
... The genetic basis of FA has received considerable attention, yet a consolidated model describing the heritability (h 2 ) of FA remains elusive. Published estimates of h 2 for FA in a range of characters and taxa are extremely variable (Hagen 1973;Møller and Thornhill 1997;Bryden and Heath 2000) and typically quite low. There is little support for the presence of any quantitative trait loci for FA (Leamy et al. 1997), but significant epistasis for FA has been demonstrated (Leamy et al. 2002). ...
... There is little support for the presence of any quantitative trait loci for FA (Leamy et al. 1997), but significant epistasis for FA has been demonstrated (Leamy et al. 2002). Nonetheless, selection can reduce trait-specific asymmetry over time (Reeve 1960;Møller and Thornhill 1997) and consequently, the degree of character asymmetry may reflect the functional impact of asymmetry on character performance (Mather 1953;Palmer and Strobeck 1986;Balmford et al. 1993;Gummer and Brigham 1995;Clarke 1998). Given this relationship, one would predict that structures that are important to the survival of prey after capture by predators would have reduced asymmetry in those habitats where selective predation is relatively strong. ...
Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations.
... Therefore, our conclusion that developmental stability has a significant additive genetic component remains solid. (Møller & Thornhill 1997b Gangestad & Simp- son 2000;Jones et al., 2001;Puts, 2010;Thornhill & Gangestad, 1999). ...
... Instead, all participants used these debates as a means of boundary work (Gieryn, 1983) Taking a closer look at the controversies, it becomes evident that the debates are not so much about content but about a certain scientific code of conduct that seems directly related to the participants' position in the disciplinary field that framed the controversy. For example, when Møller and Thornhill (1997b) responded to their commentators in Journal of Evolutionary Biology, they suggested a code of conduct that regulates the ways in which established authorities in a field (their critics) are supposed to treat newcomers (them): ...
This article analyzes several more or less public controversies around evolutionary psychology and sociobiology. It is asked how participants in the debate draw the lines between science and non-science and what is at stake in their boundary work practices. Evolutionists and their critics practice boundary work both in scientific insider debates and in public scientific controversies. All contenders agree that science is characterized by authority relations and disciplinary gatekeepers and that science is distinguished from other social practices and by a certain code of conduct. Evolutionists and their critics differ in their assessment of scientific authorities’ roles and responsibilities, in their definition of scientific code of conduct, and in their conception of the relation between science and society. The analysis offers insights into the social production of knowledge in both scientific and public discourse and into the ways in which scientists negotiate the very nature of science as such.
... The genetic and developmental basis of lateral asymmetry is a topic of wide interest (Dongen, 2006;Klingenberg, 2010;Palmer and Strobeck, 1997). A major debate concerns whether lateral asymmetry (either fluctuating asymmetry or antisymmetry) in hybrids is due to specific genotypic interactions or to a general destabilization of development in hybrids (Clarke, 1997;Moller and Thornhill, 1997;Palmer and Strobeck, 1997). Genetic dissection of this trait could reveal the extent to which these asymmetries are due to interactions among specific loci or to decanalization of the trait in hybrids through diffuse epistatic interactions and general disruption of gene regulation in hybrids. ...
The animal head is a complex structure where numerous sensory, structural and alimentary structures are concentrated and integrated, and its ontogeny requires precise and delicate interactions among genes, cells, and tissues. Thus, it is perhaps unsurprising that craniofacial abnormalities are among the most common birth defects in people, or that these defects have a complex genetic basis involving interactions among multiple loci. Developmental processes that depend on such epistatic interactions become exponentially more difficult to study in diploid organisms as the number of genes involved increases. Here, we present hybrid haploid males of the wasp species pair Nasonia vitripennis and Nasonia giraulti, which have distinct male head morphologies, as a genetic model of craniofacial development that possesses the genetic advantages of haploidy, along with many powerful genomic tools. Viable, fertile hybrids can be made between the species, and quantitative trail loci related to shape differences have been identified. In addition, a subset of hybrid males show head abnormalities, including clefting at the midline and asymmetries. Crucially, epistatic interactions among multiple loci underlie several developmental differences and defects observed in the F2 hybrid males. Furthermore, we demonstrate an introgression of a chromosomal region from N. giraulti into N. vitripennis that shows an abnormality in relative eye size, which maps to a region containing a major QTL for this trait. Therefore, the genetic sources of head morphology can, in principle, be identified by positional cloning. Thus, Nasonia is well positioned to be a uniquely powerful model invertebrate system with which to probe both development and complex genetics of craniofacial patterning and defects.
... A meta-analysis by Møller and Thornhill (1997a) initiated debates about the magnitude of the evolutionary potential of fluctuating asymmetry and developmental instability (e.g. Houle, 1997;Markow and Clarke, 1997;Palmer and Strobeck, 1997;Møller and Thornhill, 1997b), and inspired new analyses and more recent attempts to obtain average estimates (e.g. Whitlock, 1996;Van Dongen, 1998Fuller and Houle, 2003). ...
Question: How much additive genetic variance of developmental instability is maintained under a selection-mutation balance in a domesticated population of zebra finches (Taeniopygia guttata)? Methods: We estimate the heritability and coefficient of additive genetic variance (CVA) of wing and tarsus developmental instability from an animal model. Results: No significant additive genetic variance was detected. Estimates of additive genetic variance, heritabilities, and CVA were low, but, in contrast to the CV A, moderate heritabilities could not be excluded due to highly skewed distributions. Conclusions: Although domesticated for more than 100 years, reducing selection pressures, lowering genetic variation for developmental instability, and allowing the accumulation of de novo genetic variance, the CVA of developmental instability is likely to be below 2-3% in this population.
... Controversy remains as to whether fluctuating asymmetry may have an additive genetic component. Moller and Thornhill (1997) in a metaanalysis of studies on developmental stability concluded that the overall mean effect size of heritability was h 2 =0.27. Palmer and Strobeck (1997) have questioned these results. ...
... A large number of studies of different organisms have shown that there is indeed a statistically significant heritability of measures of developmental instability (Mdler and Thornhill, 1997a). Although the quality of these studies differs in a number of ways that may affect the estimates of the genetic and environmental components, independently of how the data are selected the conclusion remains stable: developmental instability has a statistically significant heritability (Houle, 1997; Leamy, 1997; Markow and Clarke, 1997; Palmer and Strobeck, 1997; Pomiankowski, 1997; Swaddle, 1997; Whitlock and Fowler, 1997; Moller and Thornhill, 1997b). The signficance of this finding is that relatives will resemble each other with respect to developmental instability, and that developmental stability may evolve. ...
This chapter discusses (1) the genetic and environmental determinants of developmental instability, (2) the relationship between developmental instability and mode of selection, and (3) the relationship between developmental instability and fitness. There is currently some controversy over whether only fluctuating asymmetry, or also the two other kinds of asymmetries, reflects developmental instability, although a number of cases clearly suggest that antisymmetry and directional asymmetry may reflect poor developmental conditions. Developmental instability can also be estimated from other measures of deviant phenotypes. Individuals with gross abnormalities, such as a position of the heart in the right side of the body cavity in some humans and four or six rather than five fingers on each hand, are termed “phenodeviants.” Their frequency is actually positively correlated with fluctuating asymmetry, and phenodeviants therefore reflect developmental instability. Directional and disruptive selection experiments generally result in an increase in asymmetry, while stabilizing selection has the opposite effect of reducing asymmetry. Because most of these experiments are performed in ways that avoid inbreeding and as they usually only last relatively few generations before any depletion of additive genetic variance has taken place, this provides the firmest evidence for the relationship between mode of selection and developmental instability.
... antisymmetry and directional symmetry may be important markers of developmental instability (Møller & Thornhill 1997). Antisymmetry occurs when a significant difference exists between sides and the larger side is randomly distributed within a sample, and directional asymmetry occurs when there is a consistent bias in a character toward greater development on one side (Palmer & Strobeck 1986). ...
This study aimed to assess the effect of sub-lethal concentrations of the insect growth regulator (IGR), diflubenzuron, on the body size of the horn fly Haematobia irritans (L.) and on its developmental stability, by fluctuating asymmetry (FA) analysis. Breeding media with different sub-lethal diflubenzuron concentrations and a control medium, were prepared to obtain morphometric measures on adult individuals. Principal component analysis was used to generate an index of general body size, using the correlation matrix of the original characters. Levels of FA and the multivariate index of size were compared among treatments. Contrary to the expectations, the exposure to diflubenzuron did not result in a significant and concomitant increase in the level of FA across treatments or in the number of individuals showing developmental instability. Nevertheless, a significant reduction of size due to the diflubenzuron may reflect the ability of H. irritans to perform physiological and morphological adjustments allowing phenotype compensation, at least to some extent, for stressful environmental conditions. On the other hand, the IGR may be selecting more symmetrical and resistant individuals. From the pest control point of view, the reduction of size may be a positive effect of the IGR since size is usually directly related to fitness.
... When taken in conjunction with previous studies of the insecticide resistance systems of L. cuprina (McKenzie & Yen 1995; Freebairn et al. 1996) the current results support this concern and help to focus other arguments. For example, there is considerable debate about the use of departures from symmetry other than £uctuating asymmetry for estimates of developmental perturbation (Graham et al. 1993; Palmer 1996; MÖller & Thornhill 1997b). ...
The dieldrin and diazinon resistance systems of the Australian sheep blowfly (Lucilia cuprina) have been used previously to relate stress, departures from bilateral symmetry, developmental stability and relative fitness. These systems are now used to consider stress and asymmetry in a developmental context. Larval to adult development is shown to be significantly impaired after arrested development at 8 degrees C, however the asymmetry score of adults of a given genotype is similar after arrested or continuous development. Selection against dieldrin-resistant and unmodified diazinon-resistant genotypes occurs during arrested development because greater proportions of these genotypes pupae at 8 degrees C than do susceptible or modified diazinon-resistant genotypes. Pre-pupae of all genotypes complete development equally successfully when transferred from 8 degrees C to 27 degrees C. Adults fail to emerge when pupae formed at 8 degrees C undergo this temperature transition. Temperature-shift experiments show the asymmetry score is determined between pre-pupal and pupal stages of the life cycle. This stage occurs at 27 degrees C in arrested and continuously developing cultures providing an explanation for the independence of stress, selective mortality during developmental arrest and asymmetry score. The results emphasize the need for genetic, environmental and developmental data before an asymmetry phenotype can be directly related to developmental stability and relative fitness.
... This study system clearly emphasized the important of epistatic interactions (McKenzie, 2003). An example where one locus appeared to affect DI more generally across different traits can be found in Mitton (1993), and other examples were reviewed by Møller & Thornhill (1997b) and Leamy & Klingenberg (2005). QTL studies have also revealed the occurrence of dominance effects but its general importance is not supported by the overall weak association between FA/DI and inbreeding (Leamy & Klingenberg, 2005). ...
The role of developmental instability (DI), as measured by fluctuating asymmetry (FA), in evolutionary biology has been the focus of a wealth of research for more than half a century. In spite of this long period and many published papers, our current state of knowledge reviewed here only allows us to conclude that patterns are heterogeneous and that very little is known about the underlying causes of this heterogeneity. In addition, the statistical properties of FA as a measure of DI are only poorly grasped because of a general lack of understanding of the underlying mechanisms that drive DI. If we want to avoid that this area of research becomes abandoned, more efforts should be made to understand the observed heterogeneity, and attempts should be made to develop a unifying statistical protocol. More specifically, and perhaps most importantly, it is argued here that more attention should be paid to the usefulness of FA as a measure of DI since many factors might blur this relationship. Furthermore, the genetic architecture, associations with fitness and the importance of compensatory growth should be investigated under a variety of stress situations. In addition, more focus should be directed to the underlying mechanisms of DI as well as how these processes map to the observable phenotype. These insights could yield more efficient statistical models and a unified approach to the analysis of patterns in FA and DI. The study of both DI and canalization is indispensable to obtain better insights in their possible common origin, especially because both have been suggested to play a role in both micro- and macro-evolutionary processes.
Much recent research has focused on the ratio of the lengths of the second to fourth manual digits (2D:4D) as a predictor of the degree of expression of sexually dimorphic and other sex-hormone-mediated traits. However, published findings are often contradictory or subject to various methodological problems. In the present study, we reassessed the relationships among three measures of 2D:4D (left hand, right hand, and mean) and several variables previously claimed to be related to 2D:4D, including sexual orientation, spatial ability, status, physical prowess, and components of reproductive success. In addition, we examined the relationship between 2D:4D measures and several other traits whose expression is thought to be related to sex hormones, including voice pitch, sociosexuality, mating success, and fluctuating asymmetry. 2D:4D measures showed highly significant sex differences, as did spatial ability, sociosexuality, components of reproductive and mating success, and fluctuating asymmetry. However, out of 57 correlations, 2D:4D correlated significantly in the predicted direction only with sexual orientation (for both sexes) and only for left hand 2D:4D. We discuss the recent 2D:4D literature in light of these findings and consider their implications for understanding the timing of developmental events.
The symmetry and masculinity of the face are often considered important elements of male facial attractiveness. However, facial preferences are rarely studied on natural faces. We studied the effect of these traits and facial metric parameters on facial attractiveness in Spanish and Colombian raters. In total, 13 metric and 11 asymmetry parameters from natural, unrnanipulated frontal face photographs of 50 Spanish men were measured with the USIA semiautomatic anthropometric software. All raters (women and men) were asked to rank these images as potential long-term partners for females. In both sexes, facial attractiveness was negatively associated with facial masculinity, and preference was not associated with facial symmetry. In Spanish raters, both sexes preferred male traits that were larger in the right side of the face, which may reflect a human tendency to prefer a certain degree of facial asymmetry. We did not find such preference in Colombian raters, but they did show stronger preference for facial femininity than Spanish raters. Present results suggest that facial relative femininity, which is expected to signal, eg good parenting and cooperation skills, may be an important signal of mate quality when females seek long-term partners. Facial symmetry appears unimportant in such long-term mating preferences.
In many studies, fluctuating asymmetry (FA) has been used as a measure of individual differences in developmental imprecision. A model of how variation in developmental imprecision is associated with variation in asymmetry is described and applied to important issues about FA. If individual differences in developmental imprecision exist, asymmetry due to developmental error should be leptokurtically distributed. Moreover, the greater the magnitude of individual differences, the greater the leptokurtosis. Asymmetry purportedly due to developmental error in a variety of species is indeed leptokurtically distributed. The level of leptokurtosis suggests that the CV in individual differences in underlying developmental imprecision is generally 20–25, consistent with it being a fitness trait. In addition, data suggest that: (1) the individual differences that underlie the developmental imprecision of different traits are largely shared across traits and not trait-specific; (2) the heritability of these individual differences may average between 35 and 55%, despite small heritabilities of individual trait FAs; and (3) correlations between FA and fitness traits or components suggest high correlations between underlying variation in developmental precision and fitness in many species. Theoretical implications are discussed.
A previous study by the authors showed that the body scent of men who have greater body bilateral symmetry is rated as more attractive by normally ovulating (non-pill-using) women during the period of highest fertility based on day within the menstrual cycle. Women in low-fertility phases of the cycle and women using hormone-based con-traceptives do not show this pattern. The current study replicated these findings with a larger sample and statistically controlled for men's hygiene and other factors that were not controlled in the first study. The current study also examined women's scent attrac-tiveness to men and found no evidence that men prefer the scent of symmetric women. We propose that the scent of symmetry is an honest signal of phenotypic and genetic quality in the human male, and chemical candidates are discussed. In both sexes, facial attractiveness (as judged from photos) appears to predict body scent attractiveness to the opposite sex. Women's preference for the scent associated with men's facial attrac-tiveness is greatest when their fertility is highest across the menstrual cycle. The results overall suggest that women have an evolved preference for sires with good genes. © 1999 Elsevier Science Inc.
Phenotypic symmetry results from both a genetic predisposition and the influence of the developmental environment. Although most studies of mate choice and phenotypic asymmetry are couched in terms of active choice for ‘good genes’, an alternative viewpoint is to consider incidental mating biases that arise from the functional effects of asymmetrical phenotypes. This paper (i) discusses the specific situations in which symmetry-based mate choice may be likely, and (ii) presents research on female mate choice and symmetry in the periodical cicada, Magicicada septendecim (L.). Male mating aggregations and lack of mating gifts or parental care make this species an ideal target for studying female choice for superior mates, and thus for a relationship between male symmetry and male mating success.
In recent years researchers from diverse disciplines in the life sciences have turned their attention to the issue of developmental stability in the organism. Their key measure, fluctuating asymmetry (FA), is defined as the random, stress-induced deviations from perfect symmetry that develop during the development of bilaterally symmetrical traits. This is regarded as a promising measure of the stress experienced by individuals during their development, as well as the interaction between genetic and environmental forces which affect that development. FA also sheds light on several domains within psychological research, such as the interplay between nature and nurture during human development, etiology of mental health, mating and choice of partners, and even perception of facial beauty. This study reviews the manifestation and sources of FA in humans, and seeks to provide some insight regarding their relevance and possible application to various domains in psychology.
Meta-analysis is the statistical synthesis of the results of separate studies. It was adapted from other disciplines for use in ecology and evolutionary biology beginning in the early 1990s, and, at the turn of the century, has begun to have a substantial impact on the way data are summarized in these fields. We identify 119 studies concerned with meta-analysis in ecology and evolution, the earliest published in 1991 and the most recent in 2000. We introduce the statistical methods used in modern meta-analysis with references to the well-developed literature in the field. These formal, statistically defensible methods have been established to determine average treatment effects across studies when a common research question is being investigated, to establish confidence limits around the average effect size, and to test for consistency or lack of agreement in effect size as well as explanations for differences in the magnitude of the effect among studies. Problems with popular but statistically flawed methods for the quantitative summary of research results have been pointed out, and their use is diminishing. We discuss a number of challenges and threats to the validity of meta-analysis in ecology and evolution. In particular, we examine how difficulties resulting from missing data, publication bias, data quality and data exclusion, non-independence among observations, and the combination of dissimilar data sets may affect the perceived utility of meta-analysis in these fields and the soundness of conclusions drawn from its application. We highlight particular applications of meta-analysis in ecology and evolution, discuss several controversies surrounding individual meta-analyses, and outline some of the practical issues involved in carrying out a meta-analysis. Finally, we suggest changes that would improve the quality of data synthesis in ecology and evolutionary biology, and predict future directions for this emerging enterprise.
Developmental stability, the ability of an individual to eliminate environmental disturbances while expressing a heritable phenotypic trait, was compared in two walnut (Juglans regia L.) populations, a natural and an artificial. Bilateral leaf morphometrics were used to estimate fluctuating asymmetry which refers to random deviation from perfect symmetry of bilateral traits resulting from extrinsic and intrinsic perturbations not buffered during development. Fluctuating asymmetry was used as a proxy of developmental stability. We analyzed our data from a Bayesian perspective showing that developmental stability levels are decreased in the natural population. Our results indicate that an attention may be directed towards the conservation of the natural walnut resources of the area. Fluctuating asymmetry as an indicator of developmental stability may contribute especially in the framework of comparative studies as a population biomonitoring tool.
Previous research indicates that the scent of developmental stability (low fluctuating asymmetry, FA) is attractive to women who are fertile (at high-conception risk points in their menstrual cycles), but not to other women or men. Prior research also indicates that the scent of dissimilarity in major histocompatibility complex (MHC) genes may play a role in human mate choice. We studied the scent attractiveness to the opposite sex of t-shirts worn for 2 nights' sleep. Our results indicate that the two olfactory systems are independent. We repeated previous results from studies of the scent of symmetry. We repeated previous results from MHC research in part; men, but not women, showed a preference for t-shirts with the scent of MHC dissimilarity. Women's scent ratings of t-shirts were uncorrelated with the wearer's MHC dissimilarity and allele frequency, but positively correlated with the wearer's MHC heterozygosity. Fertile women did not exhibit any MHC trait preferences. Women's preference for the scent of men who were heterozygous for MHC alleles may be stronger in women who are at infertile cycle points. Men preferred the scent of common MHC alleles, which may function to avoid mates with rare alleles that exhibit gestational drive. Men also preferred the scent of women at fertile cycle points. The scent of facially attractive women, but not men, was preferred. Neither FA nor facial attractiveness in either sex correlated with MHC dissimilarity to others, MHC heterozygosity, or MHC allelic rarity. Copyright 2003.
Dissertation (Ph.D.)--University of Michigan
We analysed asymmetry in the wings of the speckled wood butterfly (Pararge aegeria)by measuring area, length and width of fore- and hindwings. The type of asymmetry is fluctuating except for fore- and hindwing area, and forewing width in males, where asymmetry is directional. The amount of asymmetry (variance of the left wing minus the right wing) is less in males than in females. Within males asymmetry was directional and less in pale, predominantly territorial males than in melanic, predominantly non-territorial males. Asymmetry was negatively related to growth rate within females, but not within males. Females grew faster than males, but had higher asymmetry, whereas the more asymmetrical melanic males grew more slowly than pale males. The differences in the type and amount of asymmetry between the sexes and colour classes suggest a relationship with sex-specific flight patterns such as the territorial spiralling flight of males. We hypothesize that slightly asymmetrical males turn faster, and therefore are superior in territorial disputes over more symmetrical or extremely asymmetrical males. This implies that sexual selection via male–male competition influences the type and amount of asymmetry. The existence of more extremely asymmetrical individuals in females, and to a lesser extent in non-territorial males, may indicate that there are costs in reducing asymmetry.
Little is known about the genetic nature of human psychometric intelligence (IQ), but it is widely assumed that IQ's heritability is at loci for intelligence per se. We present evidence consistent with a hypothesis that interindividual IQ differences are partly due to heritable vulnerabilities to environmental sources of developmental stress, an indirect genetic mechanism for the heritability of IQ. Using fluctuating asymmetry (FA) of the body (the asymmetry resulting from errors in the development of normally symmetrical bilateral traits under stressful conditions), we estimated the relative developmental instability of 112 undergraduates and administered to them Cattell's culture fair intelligence test (CFIT). A subsequent replication on 128 students was performed. In both samples, FA correlated negatively and significantly with CFIT scores. We propose two non-mutually exclusive physiological explanations for this correlation. First, external body FA may correlate negatively with the developmental integrity of the brain. Second, individual energy budget allocations and/or low metabolic efficiency in high-FA individuals may lower IQ scores. We review the data on IQ in light of our findings and conclude that improving developmental quality may increase average IQ in future generations.
In recent years researchers from diverse disciplines in the life sciences have turned their attention to the issue of developmental stability in the organism. Their key measure, fluctuating asymmetry (FA), is defined as the random, stress-induced deviations from perfect symmetry that develop during the development of bilaterally symmetrical traits. This is regarded as a promising measure of the stress experienced by individuals during their development, as well as the interaction between genetic and environmental forces which affect that development. FA also sheds light on several domains within psychological research, such as the interplay between nature and nurture during human development, etiology of mental health, mating and choice of partners, and even perception of facial beauty. This study reviews the manifestation and sources of FA in humans, and seeks to provide some insight regarding their relevance and possible application to various domains in psychology.
Fruit abortion has been hypothesized to be a parental means of selective removal of propagules with low viability. In particular, aborted zygotes have been suggested to have developmentally deviant phenotypes, and surviving offspring may therefore give rise to adults with a developmentally stable phenotype. We tested predictions from this hypothesis using acorns of holm oaks Quercus ilex as a model system. Fecundity of oak trees was negatively related to mean fluctuating asymmetry of leaves, and abortion rates were positively related to leaf fluctuating asymmetry in at least one population. Aborted acorns were asymmetric in 83-99% of cases in three samples, while mature acorns were only asymmetric in 57-78% of cases. Acorn asymmetry was unrelated to germination probability and germination date, and had no significant effect on number of leaves, leaf mass, stem mass, seedling height or leaf area of seedlings. However, acorn asymmetry affected the trade-off between number and size of leaves in seedlings. Seedlings from asymmetric acorns showed a positive relationship between acorn size and number of leaves, but no relationships between acorn size and leaf area, while symmetric acorns showed the opposite. A positive relationship between acorn size and number of leaves in spring was found for naturally emerged seedlings that died during their first summer, whereas the number of leaves produced by surviving seedlings did not depend on acorn size. These findings are consistent with the hypothesis that stressed trees selectively abort propagules of low viability, and that developmental selection acts on a measure of developmental instability of fruits.
The purposes of the present study were to estimate the heritability of the fluctuating asymmetry in chickens, using the restricted maximum likelihood procedure, and to evaluate the effects of age and sex on the fluctuating asymmetry. Leg, wing, and feather lengths and ear-lobe and wattle areas were measured. In experiment 1, 1,073 birds were used from 2 generations with complete pedigree of the Quail Castellana breed to estimate the heritability for the fluctuating asymmetry at 36 wk of age. The estimated heritability of absolute fluctuating asymmetry was not significantly different from zero for all 5 traits, and similar estimates were obtained for relative fluctuating asymmetry, directional asymmetry, transformed absolute and relative fluctuating asymmetry, and 3 alternative indexes of fluctuating asymmetry. The heritability of the combined absolute or relative fluctuating asymmetry was still very low, indicating that fluctuating asymmetry was determined solely by environmental sources of variation and that fluctuating asymmetry estimates should not be confounded by appreciable additive genetic contributions. The genetic correlation between sides was not significantly different from one, indicating that differences between sides were purely environmental in origin. Different traits rarely showed much correlation in their level of fluctuating asymmetry, indicating that the level of fluctuating asymmetry in all traits did not reflect equally the quality of animals. In experiment 2, fluctuating asymmetry differences among ages and sexes were investigated at 8, 12, 16, 20, 24, 28, 32, 36, and 40 wk in 360 birds from the same breed. Significant variation with age was observed in leg length, wing length, feather length (females), and wattle area (females), which was mainly related to onset of sexual maturity and adult stage. Females showed significantly greater fluctuating asymmetry for ear-lobe area than males. There were significant differences in fluctuating asymmetry for wing length, feather length, and wattle area near the onset of sexual maturity, with males having significantly greater fluctuating asymmetry than females for wing length and the opposite being true for feather length and wattle area.
Developmental instability or noise, defined as the phenotypic imprecision of an organism in the face of internal or external stochastic disturbances, has been thought to play an important role in shaping evolutionary processes and patterns. The genetic studies of developmental instability have been based on fluctuating asymmetry (FA) that measures random differences between the left and the right sides of bilateral traits. In this article, we frame an experimental design characterized by a spatial autocorrelation structure for determining the genetic control of developmental instability for those traits that cannot be bilaterally measured. This design allows the residual environmental variance of a quantitative trait to be dissolved into two components due to permanent and random environmental factors. The degree of developmental instability is quantified by the relative proportion of the random residual variance to the total residual variance. We formulate a mixture model to estimate and test the genetic effects of quantitative trait loci (QTL) on the developmental instability of the trait. The genetic parameters including the QTL position, the QTL effects, and spatial autocorrelations are estimated by implementing the EM algorithm within the mixture model framework. Simulation studies were performed to investigate the statistical behavior of the model. A live example for poplar trees was used to map the QTL that control root length growth and its developmental instability from cuttings in water culture.
Keywords:Developmental stability;directional selection;fluctuating asymmetry;heritability;meta-analysis.
ulna in mice lacking Ferrara Comment
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- J H Barkow
- L Cosmides
- The Generation
- D M Pungirius
- P Carmeliet
- V Vandenhoeck
- A Nagy
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- A P Davis
- D P Witte
- K Carver-Moore
- M W Hillan
- Moore
- K Fowler
- D Houle
- Thornhill
- L Leamy
(Only Barkow, those not cited J. H., L. Cosmides and the Generation D. M. and Pungirius pungitius Carmeliet, P., V. Vandenhoeck. and A. Nagy. VEGT allele. Davis, A. P., D. P. Witte, ulna in mice lacking Ferrara, N., K. Carver-Moore, Hillan and M. W. Moore. of the VEGF Fowler, K. and inbreeding Houle, D. 1997. Comment and Thornhill. Leamy, L. 1997. Is developmental Leary, R. F. and F. W. Allendorf. for conservation Lewontin, R. C. 1983. Gene, from Molecules Markow, T. A. 1992. Genetics neurobiology Markow, T. A. and CT. M. giant step backward. McKenzie, J. A. and G. M. Australian in Moller and Thornhill, and J. Tooby of Culture. G. J. Boyd
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