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Cost of strepsipteran macroparasitism for immature wasps: Does sociality modulate virulence?
Abstract
An important factor modulating parasite virulence is the level of extrinsic mortality experienced by hosts. Where it is high, parasites are expected to grow or reproduce quickly to complete their lifecycle before their host is killed, whereas virulence is expected to be less under low extrinsic mortality, where growth/reproduction can be slower. A prominent example of a low mortality environment for parasites are immature social insects. Here we examined the cost of parasitism, i.e. virulence, experienced by larval and pupal stages of Polistes wasps following infection by endoparasitic Strepsiptera (under starvation conditions). We found that there was no difference in virulence between infected and uninfected individuals for the seven days following infection; either measured as host mortality or mass loss. Likewise, there was no observed cost of parasitism during the first seven days of the pupal stage of the host. Growth of the endoparasitic stages appeared the same between starved laboratory individuals and field caught samples. Strepsipteran parasites apparently enter a lag phase until the later stages of host pupal development, which we speculate reduces the negative impact of parasitism during the hosts’ critical developmental stages. Our results highlight the need for further inquiry into the influence of sociality upon the evolution of parasite virulence.
... Previous work has shown that facial pattern development is condition-dependent [24,25] and correlated with body size [15,22] but see [21,24]. Therefore, we examine whether geographic variation in facial patterns is associated with geographic variation in body size and strepsipteran parasitism that is thought to influence host development and phenotype [26,27,28]. We also explore how facial pattern variation is associated with geographic variation in climate, as climate is well known to influence invertebrate size and condition [29]. ...
... P. dominulus facial patterns are influenced by larval feeding [24,25], so strepiptera likely reduce host facial pattern brokenness via nutritional costs imposed during development. The precise nutritional cost of strepisipteran parasitism remains untested, though the cost appears to be sustainable during larval stages [26]. There is strong, consistent evidence that strepsiptera influence host development, as stylopized wasps are smaller than healthy ones [21,32], show higher levels of fluctuating asymmetry, and have less fat body depending on parasite load and sex [27]. ...
... There is strong, consistent evidence that strepsiptera influence host development, as stylopized wasps are smaller than healthy ones [21,32], show higher levels of fluctuating asymmetry, and have less fat body depending on parasite load and sex [27]. Our results suggest that strepsiptera impose a sufficient nutritional burden to reduce the advertised quality of the host, in agreement with their lack of involvement in the colony hierarchy, social life [26], and dominance interactions in winter aggregations [33]. The relationship between adult advertised quality and parasitism could also be due to strepsiptera preferential parasitizing larvae in poor condition. ...
Global environmental change cause numerous changes in the structure and functioning of terrestrial ecosystems. Novel sets of ecological indicators and biomarkers may significantly enhance existing biomonitoring programs. This thesis assess the possibilities to use colouration traits of social insects (Hymenoptera: Formicidae, Vespidae) as indicators of environmental stress. The results contribute to the developing of current methods of biomonitoring and highlight novel aspects in environmental biology of social insects.
... Previous work has shown that facial pattern development is condition-dependent [24,25] and correlated with body size [15,22] but see [21,24]. Therefore, we examine whether geographic variation in facial patterns is associated with geographic variation in body size and strepsipteran parasitism that is thought to influence host development and phenotype [26,27,28]. We also explore how facial pattern variation is associated with geographic variation in climate, as climate is well known to influence invertebrate size and condition [29]. ...
... P. dominulus facial patterns are influenced by larval feeding [24,25], so strepiptera likely reduce host facial pattern brokenness via nutritional costs imposed during development. The precise nutritional cost of strepisipteran parasitism remains untested, though the cost appears to be sustainable during larval stages [26]. There is strong, consistent evidence that strepsiptera influence host development, as stylopized wasps are smaller than healthy ones [21,32], show higher levels of fluctuating asymmetry, and have less fat body depending on parasite load and sex [27]. ...
... There is strong, consistent evidence that strepsiptera influence host development, as stylopized wasps are smaller than healthy ones [21,32], show higher levels of fluctuating asymmetry, and have less fat body depending on parasite load and sex [27]. Our results suggest that strepsiptera impose a sufficient nutritional burden to reduce the advertised quality of the host, in agreement with their lack of involvement in the colony hierarchy, social life [26], and dominance interactions in winter aggregations [33]. The relationship between adult advertised quality and parasitism could also be due to strepsiptera preferential parasitizing larvae in poor condition. ...
Understanding intraspecific geographic variation in animal signals poses a challenging evolutionary problem. Studies addressing geographic variation typically focus on signals used in mate-choice, however, geographic variation in intrasexual signals involved in competition is also known to occur. In Polistes dominulus paper wasps, females have black facial spots that signal dominance: individuals wasps with more complex 'broken' facial patterns are better fighters and are avoided by rivals. Recent work suggests there is dramatic geographic variation in these visual signals of quality, though this variation has not been explicitly described or quantified. Here, we analyze variation in P. dominulus signals across six populations and explore how environmental conditions may account for this variation. Overall, we found substantial variation in facial pattern brokenness across populations and castes. Workers have less broken facial patterns than gynes and queens, which have similar facial patterns. Strepsipteran parasitism, body size and temperature are all correlated with the facial pattern variation, suggesting that developmental plasticity likely plays a key role in this variation. First, the extent of parasitism varies across populations and parasitized individuals have lower facial pattern brokenness than unparasitized individuals. Second, there is substantial variation in body size across populations and a weak but significant relationship between facial pattern brokenness and body size. Wasps from populations with smaller body size (e.g. Italy) tend to have less broken facial patterns than wasps from populations with larger body size (e.g. New York, USA). Third, there is an apparent association between facial patterns and climate, with wasp from cooler locations tending to have higher facial pattern brokenness than wasps from warmer locations. Additional experimental work testing the causes and consequences of facial pattern variation will be important, as geographic variation in signals has important consequences for the evolution of communication systems and social behavior.
... The parasites complete their development within one or two weeks, coinciding with the emergence of the adult host (Beani, 2006;Kathirithamby, 2009). Previous studies performed with these endoparasites in social wasps have investigated infection levels, behavioural, physiological or chemical and immune system changes, protection against infection and the biology of the endoparasites and their hosts (Hughes et al. 2003(Hughes et al. , 2004aHughes and Kathirithamby, 2005;Beani, 2006;Kathirithamby and Hughes, 2006;Dapporto et al. 2007;Manfredini et al. 2007Manfredini et al. , 2010aBeani et al. 2011;Cappa et al. 2014;Kudô et al. 2014). ...
... In Brazil, studies with the genus Xenos in species of Polistinae have only been reported by Kathirithamby (2012) and Kudô et al. (2014). A greater number of studies have been performed with wasps sampled in regions with temperate climates (Hughes et al. 2004a;Hughes and Kathirithamby, 2005;Manfredini et al. 2007;Beani et al. 2011;Cook, 2014). ...
Social wasps can face many challenges during their colony cycle, including the presence of parasites. The order Strepsiptera is among the main parasites of the wasp genus Polistes. The aim of this study was to evaluate the effect of an endoparasite species on the host Polistes ferreri, with the hypothesis that females of this social wasp would undergo morphophysiological alterations as well as changes in their cuticular chemical profile caused by the obligate endoparasite. On average, parasitism was found in 10% of the colonies studied. All the parasitized females showed filamentous ovarioles without developing oocytes, which indicates a physiological castration. Moreover, the endoparasites present in the gaster of females caused its volume to increase, and the presence of endoparasites changed the cuticular chemical profiles of females, confirming our hypothesis. It is likely that this parasitism effect could hamper the maintenance of wasp colonies.
... Thus, the damage is reduced in comparison to other parasitoids (Pennacchio and Strand, 2006), but the host is unable to reproduce because it is rendered sterile. In our model system, the wasp is both ''softly invaded'' by the parasite (Manfredini et al., 2007a) and not heavily depleted during its development (Hughes and Kathirithamby, 2005). ...
... In our Xenos-Polistes system, the general hemocyte profile of the host is rather stable: spreading activity, mortality and relative abundances of two main morpho-types are not dramatically affected by the presence of the parasite, as well as THC, and this is in line with the requirement for X. vesparum to maintain the host alive and healthy (i.e. capable of fighting other possible invading pathogens), in the perspective of a long and sustainable coexistence (Hughes and Kathirithamby, 2005). This fine-tuning of host immune responses suggests that instead of decreasing the host's capacity to mount immune responses by destroying or otherwise interfering with the production of immune cells, the parasite concentrates on avoiding, whether by evasion or suppression, the responses that the hemocytes would normally mount. ...
It is unexplained how strepsipteran insects manipulate the physiology of their hosts in order to undergo endoparasitic development without being entrapped by the innate immune defences of the host. Here we present pioneering work that aimed to explore for the first time several components of the cellular and humoral immune response among immature stages of the paper wasp Polistes dominulus, in both unparasitized insects and after infection by the strepsipteran endoparasite Xenos vesparum. We carried out hemocyte counts, phagocytosis assays in vitro and antibacterial response in vivo. On the whole, hemocyte load does not seem to be drastically affected by parasitization: a non-significant increase in hemocyte numbers was observed in parasitized wasps as respect to control, while the two dominant hemocyte types were present with similar proportions in both groups. On the other hand, phagocytosis was significantly reduced in hemocytes from parasitized wasps while the antibacterial response seemed to be less effective in control. These somewhat unexpected results are discussed, along with the implications of a multiple approach in immune response studies.
... Moreover, around 15 days post-eclosion, the level of hemolymph protein in crypto-parasitized wasps was significantly lower than in the healthy ones, suggesting an ''intense metabolic activity'' of the parasite, which at the late 4th instar undergoes a great increase in size (Strambi et al., 1982). The relatively low cost of parasitism for immature wasps is equally explainable in terms of a limited and ''slow growth'' during the host's critical developmental stages (Hughes and Kathirithamby, 2005). ...
... In this sense, the extruded female, after mating and egg fertilization, has finished its main role; it becomes only a protective and suitable container rich of adipocytes and tracheae for thousands of new larvae that will progressively escape from the ventral brood opening. In line with a sustainable exploitation of the host, wasps infected by X. vesparum females spend their inactive but long life out of the colony, without any nutritional depletion (Hughes and Kathirithamby, 2005;Strambi et al., 1982) by the parasite after its extrusion. ...
Females of the endoparasite Xenos vesparum (Strepsiptera, Stylopidae) may survive for months inside the host Polistes dominulus (Hymenoptera, Vespidae). The midgut structure and function in larval instars and neotenic females has been studied by light and electron microscope and by stable carbon isotopic technique. The 1st instar larva utilizes the yolk material contained in the gut lumen, whereas the subsequent larval instars are actively involved in nutrient uptake from the wasp hemolymph and storage in the adipocytes. At the end of the 4th instar, the neotenic female extrudes with its anterior region from the host; the midgut progressively degenerates following an autophagic cell death program. First the midgut epithelial cells accumulate lamellar bodies and then expel their nuclei into the gut lumen; the remnant gut consists of a thin epithelium devoid of nuclei but still provided with intercellular junctions. We fed the parasitized wasps with sugar from different sources (beet or cane), characterized by their distinctive carbon isotope compositions, and measured the bulk (13)C/(12)C ratios of both wasps and parasites. Female parasites developing inside the wasp hemocoel are able to absorb nutrients from the host but, after their extrusion, they stop incorporating nutrients and survive thanks to the adipocytes content.
... Among the known Strepsiptera hosts, hymenopterans are highlighted, mainly with reports of parasitoidism on Apidae (Ramos 2014; Soon et al. 2011), Formicidae (Kathirithamby & Johnston 1992, 2004Hughes et al. 2003), Sphecidae (Kathirithamby et al. 2012;Kifune & Hirashima, 1987;Miller et al. 2009) and Vespidae (Hughes et al. 2004b;Kudô et al. 2014;Kumar 2013) (we adopted the parasitoidism terminology following Kathirithamby 2009). Most studies on interactions with Vespidae are focused on social wasps of the subfamily Polistinae (Hughes et al. 2003;Hughes & Kathirithamby 2005;Hughes et al. 2004a). Little is known about interactions of these parasitoids with solitary wasps of the subfamily Eumeninae, especially regarding the Brazilian fauna. ...
Interactions between Strepsiptera (Pseudoxenos Saunders, 1872) and solitary wasps (Eumeninae) are recorded for the first time in Brazil for Pachodynerus grandis Willink & Roig-Alsina, 1998. An updated worldwide checklist of the host species of Eumeninae for Pseudoxenos is provided.
... The ability of Strepsiptera to keep the host alive until completion of their life cycle might be due to the larval endoparasitic "lag phase" during the host's larval and early pupal stages. This lag phase serves to reduce the cost of parasitism during the early developmental stages of the host life cycle (Hughes and Kathirithamby 2005). This phase also enables the host to metamorphose to the adult stage, which is essential for the completion of the strepsipteran life cycle. ...
Strepsiptera parasitize a broad range of hosts, encompassing seven orders and 35 families of Insecta worldwide. Both the mitochondrial DNA and the nuclear ribosomal DNA underwent a significant burst of molecular evolution in the early history of Strepsiptera. Morphologically indistinguishable forms of Strepsiptera parasitizing several host species over large geographic areas have been documented, and morphological stasis is seen in both fossil and extant taxa. Molecular characterization has found that cryptic species are widespread in Strepsiptera. The first molecular phylogenetic analysis of the Strepsiptera revealed that the suborder Mengenillidia is the sister group of all late‐branching Stylopidia. The suborder Stylopidia consists of the family Corioxenidae, which is a sister group to the rest of Stylopidia, the infraorder Stylopiformia. The Stylopidia, which have derived characteristics, are a monophyletic group comprising the family Corioxenidae and infraorder Stylopiformia. The chapter summarizes the history of Strepsiptera host‐use across seven extant families.
... We still do not know what chemicals the larval strepsipteran produces to induce such changes. It is interesting that, in this system, the parasite enters the larval host (wasp) and thus goes through the complete development of the host from larva to adult (33). This of course offers the potential for affecting adult brain development at multiple stages of wasp development. ...
Insect behavior can be manipulated by parasites, and in many cases, such manipulation involves the central and peripheral nervous system. Neuroparasitology is an emerging branch of biology that deals with parasites that can control the nervous system of their host. The diversity of parasites that can manipulate insect behavior ranges from viruses to macroscopic worms and also includes other insects that have evolved to become parasites (notably, parasitic wasps). It is remarkable that the precise manipulation observed does not require direct entry into the insect brain and can even occur when the parasite is outside the body. We suggest that a spatial view of manipulation provides a holistic approach to examining such interactions. Integration across approaches from natural history to advanced imaging techniques, omics, and experiments will provide new vistas in neuroparasitology. We also suggest that for researchers interested in the proximate mechanisms of insect behaviors, studies of parasites that have evolved to control such behavior is of significant value.
... Xenos vesparum infest P. dominula larvae in various host larval instars in multiple colony phases [33], including early in the season when the founding queen is laying workerdestined eggs [33][34][35][36][37] (figure 1). Xenos vesparum remains endoparasitic until after the host emerges as an adult [36]. ...
Parasites can manipulate host behaviour to increase their own transmission and fitness, but the genomic mechanisms by which parasites manipulate hosts are not well understood. We investigated the relationship between the social paper wasp, Polistes dominula, and its parasite, Xenos vesparum (Insecta: Strepsiptera), to understand the effects of an obligate endoparasitoid on its host's brain transcriptome. Previous research suggests that X. vesparum shifts aspects of host social caste-related behaviour and physiology in ways that benefit the parasitoid. We hypothesized that X. vesparum-infested (stylopized) females would show a shift in caste-related brain gene expression. Specifically, we predicted that stylopized females, who would normally be workers, would show gene expression patterns resembling pre-overwintering queens (gynes), reflecting gyne-like changes in behaviour. We used RNA-sequencing data to characterize patterns of brain gene expression in stylopized females and compared these with those of unstylopized workers and gynes. In support of our hypothesis, we found that stylopized females, despite sharing numerous physiological and life-history characteristics with members of the worker caste, show gyne-shifted brain expression patterns. These data suggest that the parasitoid affects its host by exploiting phenotypic plasticity related to social caste, thus shifting naturally occurring social behaviour in a way that is beneficial to the parasitoid.
... 29 Xenos enters a lag phase during the critical developmental stages of Polistes. 32 After the emergence of all the 1st instar larvae, the host (along with the now almost empty Xenos female) will die. ''After all, if they can so completely 'castrate' the wasps without killing them, an ability obviously evolved in an association through an immense period of time, it will not be surprising to find that they also manipulate the behaviour''. ...
W. D. Hamilton (1936-2000) has been described by Richard Dawkins as ‘a good candidate for the title of most distinguished Darwinian since Darwin’. His work on evolutionary biology continues to influence scientists working across a wide variety of disciplines, including evolution, population genetics, animal behaviour, genetics, anthropology, and ecology. This third and final volume of Narrow Roads of Gene Land contains Hamilton’s key papers published between 1990 and 2000, a period in which he covered a great diversity of topics, often in collaboration with other scientists. Many of the papers in this volume continue his work on sex, and particularly its relation to parasitic disease, but other topics covered include the Gaia theory, the colours of autumn leaves, and the still-controversial hypothesis that the AIDS pandemic accidentally originated in a polio vaccination campaign in Africa. Each of the co-authored papers in this volume is preceded by an introduction written by one of Hamilton’s co-authors, following the model of the previous two volumes in this series, which brings the reader closer to Hamilton’s extraordinary personality and intellect, providing the intellectual and physical contexts within which each piece of research was developed. Also included are a chapter by Jeremy Leighton John on the Hamilton archive - ‘Bill’s last great work’ - complete with irresistible pictures, and Alan Grafen’s biographical memoir, which presents an overview of Bill’s life and work. Together, this unique collection of papers with their biographical introductions provides a profound portrait of one of the twentieth century’s most innovative scientists.
... There they enter the immature stages of the wasp through the cuticle and grow together with the host. The cost of the development of Xenos is sustainable during the larval stages of Polistes (HUGHES & KATHIRITHAMBY 2005). Non-sibling larvae were sometimes found to parasitize the same host individual (VANNINI et al. 2008). ...
Xenos vesparum, a species of the enigmatic insect order Strepsiptera is reported for the first time
from the territory of Poland from eight localities in six physiographic regions: Lower Silesia (Dolny OEl¹sk),
Trzebnickie Hills (Wzgórza Trzebnickie), Upper Silesia (Górny OEl¹sk), Kraków-Wieluñska Upland (Wy¿yna
Krakowsko-Wieluñska), Bieszczady Mts (Bieszczady), and Pieniny Mts (Pieniny). We also provide a review of
the species’ biology and its distribution in Europe.
... The successive endoparasitic stages follow without remarkable growth until the late pupal stages of the host, when the wasp is adult-like and the parasite is approximately 4-5 mm (Fig. 1). This "slow growth" could explain the apparent lack of cost of parasitism for immature wasps, in terms of mortality and lost mass (Hughes & Kathirithamby 2005). ...
The infection of Polistes dominulus wasps by the strepsipteran Xenos vesparum provides a suitable case study for exploring parasitic manipulation. One aim of this review is to summarize the life cycle of X. vesparum: from infection of immature wasps to the "stylopization" of adults, and from its mating at summer aberrant aggregations of infected wasps to the overwintering of fertilized Xenos inside the abdomen of hibernating wasps. The second aim of this review it to highlight how this parasite manipulates the flexible phenotype of the wasp to maximize its own reproductive success.
... An additional explanation for the small size of stylopized wasps may be nutrient depletion during the preimaginal stages of the host, although the cost of parasitism is bearable in terms of mortality, mass loss (Hughes & Kathirithamby 2005) and immunocompetence against pathogens (Manfredini et al. 2010b, c). A by-product of nutrient depletion caused by endoparasitism during host pupation may be the higher fluctuating asymmetry of wings found in stylopized wasps. ...
The macroparasite Xenos vesparum affects both the behaviour and the physical traits of its host, the social wasp Polistes dominulus. Female wasps, if parasitized, do not perform any social tasks and desert the colony to gather at specific sites, where the parasite mates; at the end of summer they form prehibernating clusters joined by healthy future queens to overwinter. Parasitized wasps become highly gregarious. In April, healthy wasps leave the aggregations to found new colonies, while parasitized wasps remain in overwintering groups and release parasites to infect wasp larvae only later in the season. We studied the prolonged gregarious behaviour of parasitized wasps and analysed the morphology of parasitized and healthy wasps in aggregations collected over a 7-year period to determine whether the parasite affects host size, wing symmetry, ovarian development and lipid stores. All parasitized wasps were smaller and had undeveloped ovaries and more wing fluctuating asymmetry than unparasitized wasps, irrespective of time of year, parasite load and parasite sex. If infected only by one or two X. vesparum females, the wasps had large fat bodies, which could facilitate their overwintering. In contrast, wasps infected by at least one male parasite had little lipid and died at the end of the summer. Thus, X. vesparum, may play a role in the fate of its host, by exploiting wasps' tendency to form aggregations outside the colony and by altering its caste system, nutrient allocation, diapause timing and life span to achieve its own reproduction and dispersal.
... X. vesparum does not kill its host, nor does it compromise nutrient uptake of the adult host or immunocompetence towards other pathogens (Manfredini et al. 2010a, b). There is apparently no cost of parasitism for larval wasps in terms of mortality and weight loss (Hughes and Kathirithamby 2005). However, X. vesparum induces permanent sterility in host female wasps (Strambi and Strambi 1973;Strambi et al. 1982) and alters their morphology, behaviour and fate (Beani 2006;Beani et al. 2011): this suggests that parasitization might have remarkable costs for the host at the colony level, though the fitness of infected and uninfected colonies has yet to be characterized. ...
Successful invaders often become established in new ranges by outcompeting native species. The "evolution of increased competitive ability" hypothesis predicts that invasive species are subjected to less predation and parasitization than sympatric native species, and thus can allocate resources from defence and immunity to growth and fecundity, thereby achieving higher fitness. In this study, we examined whether American invasive Polistes dominula paper wasps have reduced immunocompetence. To explore this scenario, we tested their susceptibility towards parasites and pathogens at both the individual (immune defence) and colony levels, i.e. hygienic behaviour (removal of diseased individuals by nestmates). First, we examined the response to the specific coevolved parasite Xenos vesparum (lost after invasion) in terms of individual host susceptibility and hygienic behaviour. Second, we explored the response against general pathogens by quantifying the bacterial clearance in individual wasps after a challenge with Escherichia coli and hygienic behaviour after a challenge with the fungus Beauveria bassiana. Our results show that American invasive P. dominula have a higher response against X. vesparum at the colony level, but at the individual level their susceptibility is not significantly different from conspecifics of the native range. On the other hand, invasive P. dominula display lower response after a challenge with general pathogens at both the individual and colony levels. While supporting the hypothesis of a reduction of immunocompetence towards general pathogens in invasive species, these findings also suggest that the response against coevolved parasites might follow different evolutionary pathways which are not always easily predictable.
... Due to their non-selective host-seeking behaviour (unpublished), they quickly penetrate into immatures e thus escaping possible aggressions by adult nestmates e and reach the hemocoel, where they perform all the steps of their endoparasitic development, rendering the host unable to mount an effective immune response [12]. The cost of parasitism for wasp larvae has been shown to be irrelevant in terms of mortality and mass loss [13]. This is a good example of virulence trade-off: the host is valuable to the parasite if it lives a long life [14]. ...
Host antibacterial defense after Strepsiptera parasitization is a complex and rather unexplored topic. The way how these parasites interact with bacteria invading into the host insect during an infection is completely unknown. In the present study we demonstrate that larvae of the paper wasp Polistes dominulus are more efficient at eliminating bacteria when they are parasitized by the strepsipteran insect Xenos vesparum. We looked at the expression levels of the antimicrobial peptide defensin and we screened for the activity of other hemolymph components by using a zone of inhibition assay. Transcription of defensin is triggered by parasitization, but also by mechanical injury (aseptic injection). Inhibitory activity in vitro against the Gram positive bacterium Staphylococcus aureus is not influenced by the presence of the parasite in the wasp or by a previous immune challenge, suggesting a constitutive power of killing this bacterium by wasp hemolymph. Our results suggest either direct involvement of the parasite or that defensin and further immune components not investigated in this paper, for example other antimicrobial peptides, could play a role in fighting off bacterial infections in Polistes.
... We hypothesize that the additional cuticle layers are the result of two unexpected ''ecdysless'' moults, actuated by the parasite in order to strengthen the defense barrier against host hemocytes: an ultimate attempt to confront the encapsulation process. It becomes clear that too precise expectations and comparisons with other parasites are unfeasible, because ''strepsipterans are the only parasitic insects (including parasitoids) to sequentially parasitize disparate stages of the same holometabolous host'' (Hughes and Kathirithamby, 2005) and so large a spectrum of hosts: it follows that the strategies adopted by these organisms have to be flexible and often lie outside the schemes of the other host-parasite systems. ...
To successfully complete its endoparasitic development, the strepsipteran Xenos vesparum needs to elude the defense mechanisms of its host, the wasp Polistes dominulus. SEM and TEM observations after artificial infections allow us to outline the steps of this intimate host-parasite association. Triungulins, the mobile 1st instar larvae of this parasite, are able to "softly" overcome structural barriers of the larval wasp (cuticle and epidermis) without any traumatic reaction at the entry site, to reach the hemocoel where they settle. The parasite molts 48 h later to a 2nd instar larva, which moves away from the 1st instar exuvium, molts twice more without ecdysis (a feature unique to Strepsiptera) and pupates, if male, or develops into a neotenic female. Host encapsulation involves the abandoned 1st larval exuvium, but not the living parasite. In contrast to the usual process of encapsulation, it occurs only 48 h after host invasion or later, and without any melanization. In further experiments, first, we verified Xenos vesparum's ability to reinfect an already parasitized wasp larva. Second, 2nd instar larvae implanted in a new host did not evoke any response by hemocytes. Third, we tested the efficiency of host defense mechanisms by implanting nylon filaments in control larval wasps, excluding any effect due the dynamic behavior of a living parasite; within a few minutes, we observed the beginning of a typical melanotic encapsulation plus an initial melanization in the wound site. We conclude that the immune response of the wasp is manipulated by the parasite, which is able to delay and redirect encapsulation towards a pseudo-target, the exuvia of triungulins, and to elude hemocyte attack through an active suppression of the immune defense and/or a passive avoidance of encapsulation by peculiar surface chemical properties.
... In our Xenos/Polistes system, mating and auto-infection in the same nest is unlikely, because infected wasps leave the colony before the parasites are extruded (Hughes et al. 2004 b), and mating occurs in extranidal aggregations (Beani et al. 2005 a). The successful development of more than 1 parasite of both sexes in a single specimen is probably due to the apparent lack of high cost to the host during the larval stages (Hughes and Kathirithamby, 2005). Although competition for space has been hypothesized in adult stylopized wasps (Dunkle, 1979), competition among parasites during their development is absent or very limited, therefore relaxing constraints against ' self ' as well as ' conspecific superparasitism'. ...
Host discrimination by immature host-seeking endoparasites is a complex and somewhat unexplored topic. In the case of multiple infections, conflicts among conspecifics may occur to monopolize space and resources in the same host. Two or more 1st instar larvae of Xenos vesparum (Strepsiptera, Stylopidae) may enter into a Polistes dominulus (Hymenoptera, Vespidae) larva and develop together until the adult stage of both parasite and host. We carried out a screening of mitochondrial haplotypes in X. vesparum individuals extracted from superparasitized wasps taken in 5 naturally infected nests from different areas of Tuscany (Italy), to assess whether non-sibling parasites may infect the same colony and host. In total, we obtained 12 different haplotypes out of 122 genotyped individuals of both sexes: 17 of 34 superparasitized wasps hosted parasites that originated from females differing in their haplotypes. To date, this is the first described case of superparasitism with non-sibling host-seeking larvae infecting a single individual hymenopteran host. In addition, at least in heavily infected colonies, there is evidence of a male-biased sex-ratio and synchronous development of the parasites, regardless of their haplotypes. Finally, the distribution of haplotypes per nest is consistent with either phoretic infection or larvipositing on nests by means of superparasitized wasps.
An annotated taxonomic and nomenclatural catalogue of the insect order Strepsiptera is presented. Known distributions and host associations are given as they are currently known. As of this publication, there are 627 valid species, 28 of which are known only from fossils. The misspelling of Viridipromontorius as Viridopromontoriusn. syn. (Roy and Niladri, 2016) is corrected to include Viridipromontorius aequus n. comb.Caenocholax pierci is moved to the genus Myrmecolax and becomes Myrmecolax pierci (Chattopadhyay and Chaudhuri, 1980) n. comb. Stichotrema trinadadensisGuenther, 1949) n. comb. is moved from Stichotrema to Myrmecolax. Halictophagus bohartiAbdulla, 1974 n. stat. was previously a junior synonym of Halictophagus variatus due to its being an invalid renaming of a homonym. The following species are reinstated as valid: Pseudoxenos andradeiLuna de Carvalho, 1953; Pseudoxenos atlanticusLuna de Carvalho, 1969 n. stat.; Pseudoxenos corcyricusSaunders, 1872; Pseudoxenos klugii (Saunders, 1852); Pseudoxenos lusitanicusLuna de Carvalho, 1960; Pseudoxenos schaumiiSaunders, 1872; Pseudoxenos seyrigi Monod, 1926; Stylops aburanaeKifune and Maeta, 1990 n. stat.; Stylops ainoKifune and Maeta, 1990 n. stat.; Stylops alfkeniHofeneder, 1939 n. stat; Stylops bimaculatae Perkins, 1918 n. stat.; Stylops bisalicidis Pierce, 1918 n. stat.; Stylops championi Pierce, 1918 n. stat.; Stylops collinusKifune and Maeta, 1990 n. stat.; Stylops dentataeKifune and Maeta, 1990 n. stat.; Stylops dominiqueiPierce, 1909 n. stat.; Stylops duboisi Bohart, 1937 n. stat.; Stylops duriensisLuna de Carvalho, 1974 n. stat.; Stylops esteponensisLuna de Carvalho, 1974 n. stat.; Stylops flavipedisHofeneder, 1923 n. stat.; Stylops fukuiensis Kifune, 1991 n. stat.; Stylops giganteusLuna de Carvalho, 1974 n. stat.; Stylops hirashimaiKifune and Maeta, 1990 n. stat.; Stylops izumoensisKifune and Maeta, 1990 n. stat.; Stylops krygeri Pierce, 1918 n. stat.; Stylops mandibularisPierce, 1911 n. stat.; Stylops medionitansPierce, 1919 n. stat.; Stylops moestae Pierce, 1918 n. stat.; Stylops muelleri Borchert, 1971 n. stat.; Stylops neonanae Pierce 1918 n. stat.; Stylops nipponicusKifune and Maeta, 1990 n. stat.; Stylops nitidaePasteels 1954 n. stat.; Stylops nitidiusculaePoluszyński 1927 n. stat.; Stylops oblongulusKifune and Hirashima, 1985 n. stat.; Stylops oklahomaePierce, 1909 n. stat.; Stylops orientisKifune and Maeta, 1990 n. stat.; Stylops pacificusBohart, 1936 n. stat.; Stylops perkinsiPasteels 1949 n. stat.; Stylops saliciflorisPierce, 1909 n. stat.; Stylops subcircularisKifune and Maeta, 1990 n. stat.; Stylops swenkiPierce 1909 n. stat.; Stylops truncatoidesKifune and Hirashima, 1985 n. stat. Stylops truncatusKifune and Hirashima, 1985 n. stat.; Xenos myrapetrus (Trois, 1988).
Stylopised (= parasitised by Strepsiptera Stylopidae) imagoes of Andrena (Hymenoptera Andrenidae) bees are known to exhibit intersexual morphology. Until now, their abnormal morphology has been thought to result from undernourishment of parasitised larvae during development. This hypothesis, however, dos not fit to mass provisioning Hymenoptera. We hypothesised that induced changes in the suite of morphological characters might be a consequence of manipulation of sex-specific behavioural traits by a strepsipteran parasite. Thus, the masculinised morphology of stylopised females might be connected with shifts in their sexual behaviour. Here, we tested the effect of Stylops (Strepsiptera Stylopidae) infection on the timing of spring nest emergence in Andrena bees, where males generally emerged conspicuously ear-lier than conspecific females. We used two independent data samplings – pan trapping and direct observation – to avoid possible bias caused by one of the methods. In accordance with our hypothesis, we documented that the time of emergence/activity in stylopised females follows the temporal trend of uninfected, protandrous males. We ascribe this observation to host manipulation and briefly discuss the potential adaptive value of the altered host behaviour for the parasite. We discuss our results across three species: Andrena strohmella, A. minutula and A. vaga.
The incidence of strepsipteran parasites in temperate Polistes wasps is recorded following the collection and dissection of adults from nests, foraging sites and hibernacula. The mean proportion of infected P. dominulus adults (i.e. para-site prevalence) on nests was around 7%, while wasps which were captured when hunting for prey or collecting water were rarely parasitized. Of the four Polistes species that were recovered from overwintering aggregations (dominulus, gallicus, nimphus and associus) only P. gallicus was uninfected. In P. dominulus, the most numerous host sampled, up to 25% of overwintering females were infected. We discuss our findings in the light of an extensive collation of records of Polistes parasitized by the strepsipteran genus Xenos in old and recent literature.
Strepsiptera are obligate endoparasitoids that exhibit extreme sexual dimorphism and parasitize seven orders and 33 families of Insecta. The adult males and the first instar larvae in the Mengenillidia and Stylopidia are free-living, whereas the adult females in Mengenillidia are free-living but in the suborder Stylopidia they remain endoparasitic in the host. Parasitism occurs at the host larval/nymphal stage and continues in a mobile host until that host's adult stage. The life of the host is lengthened to allow the male strepsipteran to complete maturation and the viviparous female to release the first instar larvae when the next generation of the host's larvae/nymphs has been produced. The ability of strepsipterans to parasitize a wide range of hosts, in spite of being endoparasitoids, is perhaps due to their unique immune avoidance system. Aspects of virulence, heterotrophic heteronomy in the family Myrmecolacidae, cryptic species, genomics, immune response, and behavior of stylopized hosts are discussed in this chapter.
We present the first record of parasitism of Dolichoderus bispinosus nests by Strepsiptera belonging to the family Myrmecolacidae. This becomes only the fourteenth species of ant and the fifth subfamily to be identified as a host to Strepsiptera. Of the three colonies examined all were parasitized. Prevalence of parasitism among adult ants was less than 2% in each case. However, among alate males of one colony, nearly 24% were parasitized. In conjunction with a reanalysis of previously published data we discuss the possibility that ant castes are differentially parasitized by Strepsiptera. We review the natural history of strepsipteran parasitism in ants, effects on host behaviour and incidences of parasitism in the hope of enabling detection of this parasite by myrmecologists.
This paper begins with a survey of the patterns in discovering and recording species of animals and plants, from Linnaeus' time to the present. It then outlines various approaches to estimating what the total number of species on Earth might be: these approaches include extrapolation of past trends; direct assessments based on the overall fraction previously recorded among newly studied groups of tropical insects; indirect assessment derived from recent studies of arthropods in the canopies of tropical trees (giving special attention to the question of what fraction of the species found on a given host-tree are likely to be `effectively specialized' on it); and estimates inferred from theoretical and empirical patterns in speciessizes relations or in food web structure. I conclude with some remarks on the broader implications of our ignorance about how many species there are.
Summary. hough the paper wasp genus, Polistes, is well studied, we know little of the incidence of parasitism in this group. Here we present details of 45 nest dissections for 4 species: P. dominulus (Christ), P. gallicus (L.), P. stabilinus Richards and P. carnifex (F.) to detail levels of parasitism of colony members by the obligate parasitic group of insects, the Strepsiptera. All 4 species showed evidence of parasitism among immature members. For 3 species, more than 50% of inspected nests were parasitized and the levels of parasitism among brood (larvae and pupae) was very high and did not differ significantly between parasitized nests. One species, P. stabilinus, suffered very low levels of parasitism, which may be related to its habitat choice. The number of parasites per host was positively related to the proportion of infected brood (parasite prevalence) and in some cases reached phenomenally high levels, which casts doubt on previ ously assumed mechanisms of infection for nest-making Hymenoptera, i.e. phoresy. We also document cases of egg parasitism and encapsulation in Polistes nests. Our data show that parasitism levels greatly varied among areas. Finally, the recent debate on the competitive advantage of P. dominulus in its introduced range, USA, has credited an absence of strepsipteran parasites of this species in facilitating its spread. For the first time, we document levels of parasitism for this species in its nature P range and this would appear to corroborate previous claims. We place our work in the context of other studies of parasitism of social insects and posit that the genus Polistes may have much to offer to this field.
The level of host exploitation is expected, under theory, to be selected to maximise (subject to constraints) the lifetime
reproductive success of the parasite. Here we studied the effect of two castrating trematode species on their intermediate
snail host, Potamopyrgus antipodarum. One of the trematode species, Microphallus sp., encysts in the snail host and the encysted larvae “hatch” following ingestion of infected snails by birds. The other
species, Notocotylus gippyensis, by contrast, releases swimming larvae; ingestion of the snail host is not required for, and does not aid, transmission to
the final host. We isolated field-collected snails for 3 months in the laboratory, and followed the survival of infected and
uninfected snails under two conditions: not fed and fed ad libitum. Mortality of the infected hosts was higher than mortality
of the uninfected ones, but the response to starvation treatment was parasite species specific. N. gippyensis induced significantly higher mortality in starved snails than did Microphallus. Based on these results, we suggest that host exploitation by different species of trematodes may depend on the type of transmission.
Encysting in the snail host may select for a reduced rate of host exploitation so as to increase the probability of transmission
to the final host.
Infection of the paper wasp, Polistes dominulus (Christ), by the strepsipteran parasite Xenos vesparum Rossi results in a dramatic behavioral change, which culminates in colony desertion and the formation of extranidal aggregations, in which up to 98% of occupants are parasitized females. Aggregations formed on prominent vegetation, traditional lek-sites of Polistes males, and on buildings, which were later adopted as hibernating sites by future queens. First discovered by W.D. Hamilton, these aberrant aggregations are an overlooked phenomenon of the behavioral ecology of this intensively studied wasp. For 3 months in the summer of 2000, during the peak of colony development, we sampled 91 extranidal aggregations from seven areas, numbering 1322 wasps. These wasps were parasitized by both sexes of X. vesparum, but males were more frequent from July until mid-August, during the mating season of the parasite. Aggregations were present for days at the same sites (in one case a leaf was occupied for 36 consecutive days) and were characterized by extreme inactivity. After artificial infection, parasitized "workers" deserted the nest 1 week after emergence from their cell and before the extrusion of the parasite through the host cuticle. Infected individuals did not work, were more inactive, and did not receive more aggression than did controls. We suggest that early nest desertion and subsequent aggregations by parasitized nominal workers and "future queens" is adaptive manipulation of host behavior by the parasite to promote the completion of its life cycle. Copyright 2004.
Associations between mycophagous Drosophila and nematode parasites occur throughout the temperate and boreal regions of North America, Europe, and Asia. The nematode Howardula aoronymphium has substantial adverse effects on host survival and fertility on North American Drosophila. Long-term data show that rainy summers lead to a high prevalence of parasitism in the fall and the following spring, resulting in up to a 1-yr time lag between present rainfall and increased prevalence of H. aoronymphium parasitism. A biogeographic analysis of the relative abundance of different Drosophila species has shown that H. aoronymphium may facilitate the coexistence of different species of Drosophila that compete for larval food resources. The actual host range of parasites in nature is determined by the intrinsic suitability of potential hosts for parasite infection and reproduction and various ecological factors. For H. aoronymphium in eastern North America, intrinsically suitable hosts fall within a restricted clade within the genus Drosophila. However, the temperature sensitivity of H. aoronymphium prevents it from using several host species that occur outside the geographical range of the nematodes. Finally, the host range, virulence, and geographical range of Drosophila-parasitic nematodes appear to be highly dynamic over evolutionary timescales.
Recent studies suggest that parasites (interpreted broadly to include viruses, bacteria, protozoans and helminths) may influence the numerical magnitude or geographical distribution of their host populations; most of such studies focus on the population biology and epidemiology of the host-parasite association, taking no explicit account of the genetics. Other researchers have explored the possibility that the coevolution of hosts and parasites may be responsible for much of the genetic diversity found in natural populations, and may even be the main reason for sexual reproduction; such genetic studies rarely take accurate account of the density- and frequency-dependent effects associated with the transmission and maintenance of parasitic infections. This paper aims to combine epidemiology and genetics, reviewing the way in which earlier studies fit into a wider scheme and offering some new ideas about host-parasite coevolution. One central conclusion is that 'successful' parasites need not necessarily evolve to be harmless: both theory and some empirical evidence (particularly from the myxoma-rabbit system) indicate that many coevolutionary paths are possible, depending on the relation between virulence and transmissibility of the parasite or pathogen.
Many viral, bacterial and protozoan parasites of invertebrates first propagate inside their host without releasing any transmission stages and then kill their host to release all transmission stages at once. Life history and the evolution of virulence of these obligately killing parasites are modelled, assuming that within-host growth is density dependent. We find that the parasite should kill the host when its per capita growth rate falls to the level of the host mortality rate. The parasite should kill its host later when the carrying capacity, K, is higher, but should kill it earlier when the parasite-independent host mortality increases or when the parasite has a higher birth rate. When K(t), for parasite growth, is not constant over the duration of an infection, but increases with time, the parasite should kill the host around the stage when the growth rate of the carrying capacity decelerates strongly. In case that K(t) relates to host body size, this deceleration in growth is around host maturation.
Traditional explanations for the negative fitness consequences of parasitism have focused on the direct pathogenic effects of infectious agents. However, because of the high selection pressure by the parasites, immune defences are likely to be costly and trade off with other fitness-related traits, such as reproductive effort. In a field experiment, we immunized breeding female flycatchers with non-pathogenic antigens (diphtheria-tetanus vaccine), which excluded the direct negative effects of parasites, in order to test the consequences of activated immune defence on hosts' investment in reproduction and self-maintenance. Immunized females decreased their feeding effort and investment in self-maintenance (rectrix regrowth) and had lower reproductive output (fledgling quality and number) than control females injected with saline. Our results reveal the phenotypic cost of immune defence by showing that an activated immune system per se can lower the host's breeding success. This may be caused by an energetic or nutritional trade-off between immune function and physical workload when feeding young or be an adaptive response to 'infection' to avoid physiological disorders such as oxidative stress and immunopathology.
Parasites do not always harm their hosts because the immune system keeps an infection at bay. Ironically, the cost of using immune defenses could itself reduce host fitness. This indirect cost of parasitism is often not visible because of compensatory resource intake. Here, workers of the bumblebee, Bombus terrestris, were challenged with lipopolysaccharides and micro-latex beads to induce their immune system under starvation (i.e., not allowing compensatory intake). Compared with controls, survival of induced workers was significantly reduced (by 50 to 70%).
We report here the case of a metazoan parasite, a strepsipteran, that manipulates host epidermal tissue and wraps itself within it; which probably camouflages the endoparasite and is recognized as "self" by the host. This mechanism is one of immune avoidance among parasitoid insects. The host-derived epidermal "bag" might have enabled Strepsiptera to radiate to disparate hosts compared with the relatively few taxa (596 species) described so far. They have been recorded as parasitizing 34 families belonging to seven orders of Insecta. We also report a mechanism of insect ecdysis between the first- and second-instar larva, while enclosed in the bag.
The first tylenchid parasite of ants, Formicitylenchus oregonensis n. g., n. sp., is described from a queen carpenter ant Camponotus vicinus Mayr in Western Oregon, USA. The new genus is characterised by the excretory pore anterior to the nerve-ring and rounded tails in the free-living adults, a stylet bearing basal thickenings in the free-living female, a smaller stylet lacking basal thickenings in the male and a short, crenulate leptoderan bursa. The mature parasitic female is light yellow and ovoviviparous. F. oregonensis n. sp. is closely related to members of Metaparasitylenchus Wachek, 1955, with species parasitising beetles living under bark or in rotten wood, a habitat similar to that of carpenter ants. However, males of Metaparasitylenchus are characterised by a fairly long tail with a broad peloderan bursa. It is suggested that this case of tylenchid parasitism in ants is an example of environmental host selection. A review of the described nematode parasites of ants is presented.
Due to its extreme sexual dimorphism and disparate hosts, no female myrmecolacid has been matched to its conspecific male to date. Here, for the first time to our knowledge, a morphological description is given of the matched female and male myrmecolacid, Caenocholax fenyesi waloffi ssp. nov. from Veracruz, Mexico: the female parasitic in a cricket and the male parasitic in an ant. For examined segments of DNA, the male and female are identical. Male C. fenyesi Pierce sensu lato was described 94 years ago from Veracruz. The male from Texas USA, which, for the same DNA segments, shows 15% divergence from the morphologically identical male from Veracruz, is given subspecies status, and is named Caenocholax fenyesi texensis ssp. nov. The discovery of the female finally enables many interesting studies to be pursued, such as speciation in morphologically cryptic taxa, the sexes of which parasitize disparate hosts. Caenocholax fenyesi sensu lato may also be evaluated for biocontrol of the red imported fire ant, Solenopsis invicta Buren, which is a pest in the USA and Australia.
A Smithsonian project to characterize the entire arthropod fauna of a small patch of tropical rainforest canopy from Manu National Park, in Amazonian Peru, is currently underway. Though several studies have addressed the questions of species richness, biomass, and guild composition (e.g. Moran and Southwood 1982; Southwood et al. 1982; Adis et al. 1984), the Smithsonian project is an attempt to determine the number of species as well as the abundance of each species. This chapter presents a preliminary description and analysis of the ant fauna collected as part of this project.
Why do parasites harm their hosts? Intuition suggests that parasites should evolve to be benign whenever the host is needed for transmission. Yet a growing theoretical literature offers several models to explain why natural selection may favor virulent parasites over avirulent ones. This perspective first organizes these models into a simple framework and then evaluates the empirical evidence for and against the models. There is relatively scant evidence to support any of the models rigorously, and indeed, there are only a few unequivocal observations of virulence actually evolving in parasite populations. These shortcomings are surmountable, however, and empirical models of host-parasite interactions have been developed for many kinds of pathogens so that the relevant data could be acquired in the near future.
It is predicted that host exploitation should evolve to maximize parasite fitness and that virulence (= parasite-induced host mortality) evolves along with the rate of host exploitation. If the life expectancy of a parasite is short, it is expected to evolve a higher rate of host exploitation and therefore higher virulence because the penalty to the parasite for killing the host is reduced. We tested this hypothesis by keeping for 14 months the horizontally transmitted microsporidian parasite Glugoides intestinalis in mono-clonal host cultures (Daphnia magna) under conditions of high and low host background mortality. High host mortality, and thus parasite mortality, was achieved by replacing weekly 70-80% of all hosts in a culture with uninfected hosts from stock cultures (Replacement lines). In the low-mortality treatment no replacement took place. Contrary to our expectation, parasites from the Replacement lines evolved a lower within-host growth rate and virulence than parasites from the Nonreplacement lines. Across lines we found a strong positive correlation between within-host growth rate and virulence. We did further experiments to answer the question why our data did not support the predictions. Sporophorous vesicles (SVs, spore clusters) were smaller in doubly infected than in singly infected host-gut cells, indicating that competition within cells bears costs for the parasite. Due to our experimental protocol, the average life span of infections had been much higher in the Nonreplacement lines. Since the number of parasites inside a host increases with the time since infection, long-lasting infections led to high frequencies of multiply infected host-gut cells. Therefore, we speculated that within-cell competition was more severe in the Nonreplacement lines and may have led to selection for accelerated within-host growth. SVs in the Nonreplacement lines were indeed significantly larger. Our results point out that single-factor explanations for the evolution of virulence can lead to wrong predictions and that multiple infections are an important factor in virulence evolution.
Infection of the paper wasp, Polistes dominulus (Christ), by the strepsipteran parasite Xenos vesparum Rossi results in a dramatic behavioral change, which culminates in colony desertion and the formation of extranidal aggregations, in which up to 98% of occupants are parasitized females. Aggregations formed on prominent vegetation, traditional lek-sites of Polistes males, and on buildings, which were later adopted as hibernating sites by future queens. First discovered by W.D. Hamilton, these aberrant aggregations are an overlooked phenomenon of the behavioral ecology of this intensively studied wasp. For 3 months in the summer of 2000, during the peak of colony development, we sampled 91 extranidal aggregations from seven areas, numbering 1322 wasps. These wasps were parasitized by both sexes of X. vesparum, but males were more frequent from July until mid-August, during the mating season of the parasite. Aggregations were present for days at the same sites (in one case a leaf was occupied for 36 consecutive days) and were characterized by extreme inactivity. After artificial infection, parasitized "workers" deserted the nest 1 week after emergence from their cell and before the extrusion of the parasite through the host cuticle. Infected individuals did not work, were more inactive, and did not receive more aggression than did controls. We suggest that early nest desertion and subsequent aggregations by parasitized nominal workers and "future queens" is adaptive manipulation of host behavior by the parasite to promote the completion of its life cycle. Copyright 2004.
Tested the slow growth/higher mortality hypothesis for a leaf-gallig sawfly Pontania sp. (near P. pacifica) on arroyo willow Salix lasiolepis, predicting that bigger and more rapidly developing sawflies (and galls) should be less vulnerable to attack from natural enemies. The most rapidly developing sawflies were more likely to be attacked by ectoparasitoids, probably because they were superior resources for the parasitoids. Prolonged larval development does not invariably enhance enemy attack. The slow growth/higher mortality hypothesis should not be invoked in the future without empirical support. A population of galling sawflies was studied n Arizona. The Pontania sp. (Hymenoptera: Tenthredinidae) sawflies are attacked by 2 ectoparasitoids (Bracon angelesius and Pteromalus sp.), which pierce the gall wall and lay an egg on the host Pontania sp. larva when it has reached the penultimate or ultimate instar. The ectoparasitoid paralyzes the sawfly larva before depositing the egg, so it is not possible for parasitoid attack to increase herbivore size, longevity, or development rate in this system; herbivore feeding and development cease when it is paralyzed.-from Authors
Why do parasites harm their hosts? Intuition suggests that parasites should evolve to be benign whenever the host is needed for transmission. Yet a growing theoretical literature offers several models to explain why natural selection may favor virulent parasites over avirulent ones. This perspective first organizes these models into a simple framework and then evaluates the empirical evidence for and against the models. There is relatively scant evidence to support any of the models rigorously, and indeed, there are only a few unequivocal observations of virulence actually evolving in parasite populations. These shortcomings are surmountable, however, and empirical models of host-parasite interactions have been developed for many kinds of pathogens so that the relevant data could be acquired in the near future. Aside from academic interest, the evolution of virulence has potential medical and agricultural ramifications that may provide evolutionary biology with opportunities for contributions to human welfare. For example, understanding the evolution of parasite virulence may help us design better vaccines, prevent the emergence of highly virulent strains in the future, and diminish the virulence of present pathogens. These potential applications notwithstanding, the usefulness of an evolutionary theory of virulence to social problems has not been demonstrated and is even doubtful in some cases. One promising area for contributions from evolutionary theory is in designing live, attenuated vaccines.
This paper begins with a survey of the patterns in discovering and
recording species of animals and plants, from Linnaeus' time to the
present. It then outlines various approaches to estimating what the
total number of species on Earth might be: these approaches include
extrapolation of past trends; direct assessments based on the overall
fraction previously recorded among newly studied groups of tropical
insects; indirect assessment derived from recent studies of arthropods
in the canopies of tropical trees (giving special attention to the
question of what fraction of the species found on a given host-tree are
likely to be `effectively specialized' on it); and estimates inferred
from theoretical and empirical patterns in speciessizes relations or in
food web structure. I conclude with some remarks on the broader
implications of our ignorance about how many species there are.
Why is there variation in the virulence of infectious diseases? Virulence can have substantial effects on the genetic contribution of both host and pathogen to future generations. Understanding it therefore requires explanation not only in terms of cellular and molecular mechanisms1, 2, but also in evolutionary terms: what is the nature of the selection acting on genes responsible for virulence?
Among the most important trade-offs in life history evolution is whether to grow larger at the cost of longer development time, or to develop more rapidly at the cost of reduced size. For insect herbivores, resolution of this trade-off is thought to be strongly influenced by feeding ecology and mortality risks. In contrast, how these factors might affect the developmental strategies of third trophic level organisms, like parasitoid wasps, is less understood. To address this question, we compared the development of larval endoparasitoids in the families Ichneumonidae and Braconidae that parasitize larval stage herbivores in the order Lepidoptera. The campoplegine ichneumonid Venturia canescens parasitized concealed hosts and exhibited a developmental strategy that favored progeny size over development time. In contrast, the closely related ichneumonid Campoletis sonorensis parasitized exposed hosts and exhibited the opposite strategy of favoring rapid development time over size. The microgastrine braconid Microplitis croceipes attacks partially concealed hosts and showed evidence of a trade-off between maximizing body size and minimizing development times. These results suggested that parasitoids attacking apparent, foliar-feeding hosts may favor rapid development time over size while parasitoids that attack concealed hosts favor size over development time. A broader survey of the literature supported the trends found in our experimental studies. The braconids and ichneumonids examined in this study also exhibit distinct differences in larval feeding and pupation behavior. These developmental traits did not appear to affect the size-development time continuum. However, these traits may affect the size range of hosts that larval endoparasitoids can successfully exploit.
It is predicted that host exploitation should evolve to maximize parasite fitness and that virulence ( parasite-induced host mortality) evolves along with the rate of host exploitation. If the life expectancy of a parasite is short, it is expected to evolve a higher rate of host exploitation and therefore higher virulence because the penalty to the parasite for killing the host is reduced. We tested this hypothesis by keeping for 14 months the horizontally transmitted microsporidian parasite Glugoides intestinalis in mono-clonal host cultures (Daphnia magna) under conditions of high and low host background mortality. High host mortality, and thus parasite mortality, was achieved by replacing weekly 70-80% of all hosts in a culture with uninfected hosts from stock cultures (Replacement lines). In the low-mortality treatment no replacement took place. Contrary to our expectation, parasites from the Replacement lines evolved a lower within-host growth rate and virulence than parasites from the Nonreplacement lines. Across lines we found a strong positive correlation between within-host growth rate and virulence. We did further experiments to answer the question why our data did not support the predictions. Sporophorous vesicles (SVs, spore clusters) were smaller in doubly infected than in singly infected host-gut cells, indicating that competition within cells bears costs for the parasite. Due to our experimental protocol, the average Life span of infections had been much higher in the Nonreplacement lines. Since the number of parasites inside a host increases with the time since infection, long-lasting infections led to high frequencies of multiply infected host-gut cells. Therefore, we speculated that within-cell competition was more severe in the Nonreplacement fines and may have led to selection for accelerated within-host growth. SVs in the Nonreplacement fines were indeed significantly larger. Our results point out that single-factor explanations for the evolution of virulence can lead to wrong predictions and that multiple infections are an important factor in virulence evolution.
A fundamental assumption of coevolutionary models of host-parasite relations is that resistance is costly. Costs are envisioned as phenotypic or genetic trade-offs in the allocation of limited resources to specific tasks. Using workers of the bumble bee Bombus terrestris L., we tested experimentally whether foraging effort, an energetically costly and crucially important task that ensures colony growth, survival and reproduction, is costly in terms of reduced resistance against parasite attack. The experiment showed that indeed workers allowed to forage showed lower levels of immunocompetence, as measured by the degree of encapsulation of a novel antigen, than workers prevented from foraging activity.
The reduction in larval populations of Dacus cacuminatus (Hering) and D. halfordiae (Tryon) by frugivorous vertebrates feeding on their major host fruits was studied in an endemic rainforest habitat in south-east Queensland. Throughout the spring and summer season, 66% of Solanum mauritianum Scop. fruit (D. cacuminatus host) was eaten by Macropygia phasianella (Temminck), the brown pigeon; this increased to 77% during the fruit fly's breeding season (November-January). The peak feeding time of the birds, the breeding season of the flies, and the peak fruiting season of the plants all coincided. Parasitism of D. cacuminatus by Hymenoptera, Biosteres kraussi (Fullaway) and B. oophilus (Fullaway), never exceeded 16-17%. Rodents consumed larvae in 78% of fallen fruit of Planchonella australis (R. Br.) Pierre (D. halfordiae host). It is proposed that frugivorous predators are the major natural enemies of larvae of tropical Tephritidae in their endemic habitat.
A new family of Strepsiptera (Dipterophagidae) from Australia containing a new genus and species (Dipterophagus daci) is described and figured. This is the first species of Strepsiptera to be described as a parasite of Diptera. D.daci is recorded from ten fruit fly species, viz Dacus aquilonis (May), D.bellulus Drew, D.cacuminatus (Hering), D.decurtans (May), D.mayi Hardy, D.neohumeralis Hardy, D.peninsularis Drew, D.tenuifascia (May), D.tryoni (Froggatt) and Dacus sp. n. (near musae). Gregarious parasitism (two to six adult parasites per fly) is common.
Parasitoid wasps have long been favored organisms for fundamental studies on reproductive strategies and life-history evolution. Progeny allocation models designed with parasitoids in mind assume that offspring develop by consuming most or all of the resources available from a single host, and that size is the most important factor affecting offspring fitness. Many parasitoids exhibit host usage patterns consistent with these assumptions, but our recent observations suggested that endoparasitic wasps in the family Braconidae often do not. To investigate how differences in host usage patterns might affect developmental strategies, we compared two related braconids with contrasting host usage patterns. Apanteles carpatus consumed virtually all host tissues during immature development, whereas Microplitis demolitor fed exclusively on host hemolymph and consumed a relatively small proportion of available host resources. Development time of M. demolitor was unaffected by host size, whereas development time of A. carpatus was much longer in small hosts than in large hosts. On the other hand, offspring size in M. demolitor correlated strongly with host size, but it correlated only weakly with host size in A. carpatus. Our results collectively suggest that selection has favored rapid development at the potential cost of reduced size in M. demolitor, and increased size at the potential cost of increased development time in A. carpatus. Tissue feeding appears to be more prevalent among parasitoids overall, but hemolymph feeding is the predominant pattern of host usage in several subfamilies of endoparasitic braconids. We argue that the relative importance of offspring size and development time will be influenced by host ecology and the effects of selected traits on parasitoid survival.
Parasites typically reduce host survival or fecundity. To minimize fitness loss, hosts can make temporal adjustments of their reproductive effort. To date such plastic shifts of life-history traits in response to parasitism are only known from solitary organisms where infected individuals can react by themselves. In the case of social insects, where brood care and reproductive effort is shared between reproductive individuals (typically the queen) and workers, adjustments of the reproductive effort would depend on collective decision-making. We tested for this possibility by experimentally activating the immune response of individual workers in colonies of the bumblebee, Bombus terrestris L. This induction resulted, in combination with environmental conditions, in a reduction of fitness of the social unity (i.e. colony success, measured by number and biomass of offspring) and a collective response towards earlier reproduction. As both phenomena are expressed at the level of the colony, the result suggests that key elements of the use of immune defence have been maintained through the evolutionary transition to sociality.
Parasite virulence affects both the temporal dynamics of host-parasite relationships and the degree to which parasites regulate host populations. If hosts can compensate for parasitism, then parasites may exhibit condition-dependent virulence, with high virulence being seen only when the host is under conditions of stress. Despite their usually low level of virulence, theory suggests that such parasites may still affect host population dynamics. We tested whether a trypanosome intestinal parasite of bumblebees, Crithidia bombi, expresses condition-dependent virulence. Hosts were infected with the parasite and then kept under either favourable or starvation (stressed) conditions. Under favourable conditions the infection caused no mortality, while when hosts were starved the infection increased the host mortality rate by 50%. In addition, we found a parasite-related change in host resource allocation patterns. Infected bees invested relatively more resources into their fat body and less into their reproductive system than did non-infected bees. Whether this reallocation is parasite-driven, to enhance transmission, or a host-response to parasitism, remains unknown.
Some statistical problems are added to the growing list of cautionary tales regarding the use of the conventional, ratio-based nutritional indices (RCR, RGR, ECI, AD and ECD). Analysis of ratios is based on the, probably unrealistic, assumption of an isometric relationship between denominator and numerator variables. Analysis of covariance (ANCOVA) makes less restrictive assumptions, and additionally provides important information about the data which is lost by using ratio variables. We demonstrate, using computer-generated data sets, some of the pitfalls of statistical analysis of ratios and illustrate how these may be avoided using ANCOVA. Some possible consequences of such statistical iniquities for biological interpretations are discussed.
1.
Im Oberschlundganglion der Sandbiene Andrena vaga Pz. lassen sich neurosekretorische Zellen in der Pars intercerebralis nachweisen. Eine zweite Gruppe neurosekretorischer Zellen schliet sich posterior an die vordere an. Die ableitenden Axone beider Gruppen werden beschrieben sowie der Verlauf der Nervi corporis eardiaci und der Nervi corporis allati.
2.
Das Unterschlundganglion enthlt zwei kappenartig aufsitzende Regionen neurosekretorischer Zellen.
3.
Ein Ganglion hypocerebrale fehlt, der Nervus recurrens ist urpaar und steht mit den Corpora cardiaca und Corpora allata nicht in Verbindung.
4.
Die Corpora cardiaca sind aus verschiedenen Zellelementen kompliziert aufgebaute Organe, denen wahrscheinlich auer der Speicherung und Verteilung des Neurosekrets sowie der Produktion eines eigenen Sekrets noch andere Funktionen zugesprochen werden mssen.
5.
Stichproben an den Corpora allata mnnlicher Sandbienen ergaben ein Verhltnis des Volumens der Corpora allata von gesunden zu stylopisierten Tieren wie 2 zu 1. Die unterentwickelten Corpora allata fanden sich sowohl bei Andrena-/Strylops- als auch bei Andrena-/Strylops-.
6.
Eine Volumenzunahme der Corpora allata auf das 2–3fache und erhhte Aktivitt der allata-Zellen sind bei gesunden Sandbienen- im Zusammenhang mit Dotterproduktion und Eireifung zu beobachten.
7.
Im Falle der Andrena-/Stylops- ist die Hemmung der Corpora allata sehr gering und dauert auch nur so lange, wie sich der Parasit im Wirt befindet. Im Falle Andrena/Stylops- jedoch werden das Wachstum wie auch die normale Funktion der allata-Zellen ganz unterdrckt.
8.
Die Beziehungen zwischen Corpora allata und Ovar werden besprochen. Bei Andrena-/Stylops- beruht die Hemmung von Corpora allata und Ovar des Wirtes sehr wahrscheinlich auf einem Eiweimangel. Das Eiwei wird dem Wirt wahrscheinlich whrend seiner Verpuppung von den noch nicht verpuppten zuknftigen Stylops-Weibchen entzogen.
9.
Der Fettkrper wird bei gesunden und stylopisierten Sandbienen- bis auf einen Rest langsam abgebaut.
10.
Versuche, die Wirkung des weiblichen Parasiten durch Herausnehmen aus ihren Wirten aufzuheben, andererseits durch Injektionen von Parasitenextrakten in Versuchstiere (Triatome infestans
Neiva) ihre Wirksamkeit zu prfen, muten aus Materialmangel abgebrochen werden.
We have studied the optimal growth schedule of a pathogen, which maximizes the total number of transmissions from an infected host to other individuals until host death or recovery. It is assumed that both transmission rate f(N) and host mortality increase with the number of pathogens, N. The model predicts that the optimal growth schedule of pathogens strongly depends on the curvature of f(N): If f(N) increases faster than linearly with N, the pathogens should always reproduce at the maximum speed. By contrast, if f(N) saturates with N, the optimal schedule is composed of (1) a brief initial stage of infection, in which the pathogens proliferate at the maximum speed (productive cycle), (2) followed by the long latent period with the “stationary infection level,” N∗ (latent cycle), (3) which may end when the pathogens start rapid proliferation triggered either by the host's senescence (“programmed break”) or by the sudden rise in the host's mortality (“incidental break”). The latter may be caused by the double infection of another strain. We also examine the Nash equilibrium schedule of pathogen growth in the presence of multiple infections.
Reciprocal selection is the underlying mechanism for host-parasite coevolutionary arms races. Its driving force is the reduction of host lifespan or fecundity that is caused by a parasite. Parasites evolve to optimize host exploitation, while hosts evolve to minimize the 'parasite-induced' loss of fitness (virulence). Research on the evolution of virulence has mostly emphasized the role of parasite evolution in determining virulence. However, host evolution, accelerated by sexual recombination, contributes to the evolution and expression of virulence as well. The Red Queen hypothesis predicts that genetic variation among host offspring facilitates selection for reduced virulence. Here, we outline a synthesis between current thinking about the evolution of virulence and the evolution of sex.
One possible reason for the continued neglect of statistical power analysis in research in the behavioral sciences is the inaccessibility of or difficulty with the standard material. A convenient, although not comprehensive, presentation of required sample sizes is provided here. Effect-size indexes and conventional values for these are given for operationally defined small, medium, and large effects. The sample sizes necessary for .80 power to detect effects at these levels are tabled for eight standard statistical tests: (a) the difference between independent means, (b) the significance of a product-moment correlation, (c) the difference between independent rs, (d) the sign test, (e) the difference between independent proportions, (f) chi-square tests for goodness of fit and contingency tables, (g) one-way analysis of variance, and (h) the significance of a multiple or multiple partial correlation.
According to conventional wisdom, parasites and pathogens should evolve reduced virulence to their hosts, because more virulent parasites and pathogens are more likely to drive their hosts, and themselves, to extinction. But this view has been criticized for its reliance on group selection. According to an alternative perspective, selection will favor whatever level of virulence maximizes the rate of increase of the parasite or pathogen. This optimum virulence depends on the functional relationship between a parasite or pathogen's transmissibility and its effect on host mortality, with selection often favoring an intermediate degree of virulence. The thesis of this paper is that models in which intermediate levels of virulence are favored lead quite naturally to the further conclusion that parasites and pathogens should-up to a point-become less virulent over time, once the feedbacks between ecological and evolutionary processes are incorporated into the analysis. As a consequence of successive adaptations by the parasite or pathogen, the density of susceptible hosts is reduced, thereby altering the balance between selective forces so as to favor reduced virulence. However, the evolutionarily stable strategy that is achieved is bounded away from complete avirulence. We conclude that models in which intermediate virulence is favored do not necessarily contradict the conventional wisdom in the long run; in fact, these models provide a simple mechanistic explanation for the evolution of reduced virulence.
Why is there variation in the virulence of infectious diseases? Virulence can have substantial effects on the genetic contribution of both host and pathogen to future generations. Understanding it therefore requires explanation not only in terms of cellular and molecular mechanisms1, 2, but also in evolutionary terms: what is the nature of the selection acting on genes responsible for virulence?
A well-known result from the theory of the evolution of virulence is the prediction that the virulence of a pathogen (i.e. the rate of parasite-induced host mortality) always evolves to higher levels when host background mortality rates increase. This prediction, however, is derived from models that assume that host mortality sources combine additively to determine the overall host mortality rate. In this paper, we suggest that such additivity is probably rare for many host-pathogen systems, and explore how the predictions for the evolution of virulence are altered when interactions between host mortality sources are incorporated into the theory. Our results indicate that if mortality-source interactions are sufficiently strong then the evolutionarily stable level of virulence can actually decrease as the background mortality rate increases. Consequently, a detailed mechanistic description of how parasites and other mortality sources combine to cause host mortality is required before reliable predictions about virulence evolution can be made. Moreover, mortality-source interactions make empirical comparisons of the virulence of different parasites a much more subtle issue.
Parasitoids are a group of insects whose larvae develop on or in the bodies off other insects, which they eventually kill. The majority of parasitoids are wasps (Hymenoptera) or files (Diptera), and they are numerically very abundant and important in nearly all terrestrial ecosystems. The entry explores the diversity of life histories found in parasitoids, and the physiological and behavioral adaptations of endoparasitoids to developing inside their host. It also discusses their importance as model systems for investigating major issues in evolutionary theory, for example, the sex ratio. Parasitoids are important in population ecology because they regulate or control the populations of many of their hosts. The entry discusses their population biology and their use in agriculture and forestry as biological control agents.
Influence du développement du paraiste Xenos vesparum Rossi (Insecte, Strepsitere) sur le systéme neuroendocrinien des femelles de Polistes (Hyménoptère, Vepside) au debut de leur vie imaginale
- Strambi A.
Strambi, A. and Strambi, C. 1973. Influence du de ´veloppement du paraiste Xenos vesparum Rossi (Insecte, Strepsitere) sur le syste ´me neuroendocrinien des femelles de Polistes (Hyme ´nopte `re, Vepside) au debut de leur vie imaginale. ?/ Arch. D’Anat. Microsc. Exp. 62: 39?/54