Demasculinization of male guppies increases resistance to a common and harmful ectoparasite

Parasites are detrimental to host fitness and therefore should strongly select for host defence mechanisms. Yet, hosts vary considerably in their observed parasite loads. One notable source of inter-individual variation in parasitism is host sex. Such variation could be caused by the immunomodulatory effects of gonadal steroids. Here we assess the influence of gonadal steroids on the ability of guppies (Poecilia reticulata) to defend themselves against a common and deleterious parasite (Gyrodactylus turnbulli). Adult male guppies underwent 31 days of artificial demasculinization with the androgen receptor-antagonist flutamide, or feminization with a combination of flutamide and the synthetic oestrogen 17 β-estradiol, and their parasite loads were compared over time to untreated males and females. Both demasculinized and feminized male guppies had lower G. turnbulli loads than the untreated males and females, but this effect appeared to be mainly the result of demasculinization, with feminization having no additional measurable effect. Furthermore, demasculinized males, feminized males and untreated females all suffered lower Gyrodactylus-induced mortality than untreated males. Together, these results suggest that androgens reduce the ability of guppies to control parasite loads, and modulate resistance to and survival from infection. We discuss the relevance of these findings for understanding constraints on the evolution of resistance in guppies and other vertebrates

Lesser snow goose helminths show recurring and positive parasite infection-diversity relations

The patterns and mechanisms by which biological diversity is associated with parasite infection risk are important to study because of their potential implications for wildlife population's conservation and management. Almost all research in this area has focused on host species diversity and has neglected parasite diversity, despite evidence that parasites are important drivers of community structure and ecosystem processes. Here, we assessed whether presence or abundance of each of nine helminth species parasitizing lesser snow geese (Chen caerulescens) was associated with indices of parasite diversity (i.e. species richness and Shannon's Diversity Index). We found repeated instances of focal parasite presence and abundance having significant positive co-variation with diversity measures of other parasites. These results occurred both within individual samples and for combinations of all samples. Whereas host condition and parasite facilitation could be drivers of the patterns we observed, other host- or parasite-level effects, such as age or sex class of host or taxon of parasite, were discounted as explanatory variables. Our findings of recurring and positive associations between focal parasite abundance and diversity underscore the importance of moving beyond pairwise species interactions and contexts, and of including the oft-neglected parasite species diversity in infection-diversity studies

Explaining parasite aggregation: More than one parasite species at a time

Studies generally have neglected parasite-centric views in explorations of whether the oft-seen patterns of parasite aggregation are adaptive. Using simulation models, we explored the effects of aggregation on coinfection with hetero- or conspecific parasite species characterised by different mean abundances. Increasing aggregation increased the probability of conspecific co-occurrence for parasites with low mean abundances, and increased median numbers of conspecifics for all species. In comparison, increasing aggregation generally decreased the probability, intensity and diversity of heterospecific co-occurrence, irrespective of mean abundance. Researchers should weigh the respective costs and benefits of increasing co-occurrence with conspecifics and decreasing coinfection with heterospecifics in explaining aggregation

Parasite infection leads to widespread glucocorticoid hormone increases in vertebrate hosts: A meta-analysis

Parasites and pathogens (hereafter parasites) commonly challenge organisms, but the extent to which their infections are physiologically stressful to hosts remains unclear. Importantly, vertebrate hormones, glucocorticoids (GCs), have been reported to increase, decrease or show no alterations stemming from infections, challenging the generality of parasite-associated GC responses and motivating a search for important moderator variables. We undertook the first meta-analysis of changes in vertebrate GCs following experimental infection with parasites, extracting 146 effect sizes from 42 studies involving 32 host and 32 parasite species to test for general patterns of GC following infection, as well as the influence of moderators. Overall, infection increased GCs relative to preliminary or control levels when the single largest effect sizes from repeated measures studies were examined, suggesting that parasites of vertebrate hosts can be thought of generally as physiological stressors by elevating GCs. When all effect sizes were included along with the moderator of sampling time post-infection (tPI), parasite infection still had a positive effect on host GCs. However, the strength of that effect did not relate consistently to tPI, illustrating temporal differences in GC changes during the course of infection among parasite taxa (e.g. arthropod vs. bacterial infections). Other moderator variables examined did not influence GC responses. Studies broadening the range of host and parasite taxa, and sampling during critical time windows, would aid in our understanding of variation in the host stress response and its consequences for fitness of both vertebrate hosts and their parasites

Dargent_et_al_disassortative

Data based on video and photos of female mate choice trials. See publication for details

Data from: Female preference for novel males constrains contemporary evolution of assortative mating in guppies

Progress toward local adaptation is expected to be enhanced when divergent selection is multi-dimensional, because many simultaneous sources of selection can increase the total strength of selection and enhance the number of independent traits under selection. Yet, whether local adaptation ensues from multi-dimensional selection also depends on its potential to cause the build-up of reproductive barriers such as sexual signals and preference for these signals. We used replicate experimental introductions of guppies (Poecilia reticulata) in nature to test whether an abrupt and dramatic shift in multiple important ecological dimensions (at a minimum: parasitism, predation, and diet/resources) promoted the contemporary evolution of assortative mating. After 8-12 post-introduction guppy generations in the wild, we bred descendants of each population in a common-garden laboratory environment for two generations, after which we recorded the preferences of females from each population for males from each population. We found contemporary evolution of male traits (size, body condition, colour) that should influence mate choice, but no evidence for the occurrence of positive assortative preferences. That is, females in a given evolving population did not prefer males from that population over males from other populations. Instead, females tended to prefer novel males (i.e. disassortative mating), which likely acts as a mechanism preventing the evolution of reproductive isolation. Preferences for novelty may explain why many cases of local adaptation do not lead to the evolution of reproductive barriers and ecological speciation

Data from: Parting ways: Parasite release in nature leads to sex-specific evolution of defense

We evaluate the extent to which males and females evolve along similar or different trajectories in response to the same environmental shift. Specifically, we use replicate experimental introductions in nature to consider how release from a key parasite (Gyrodactylus) generates similar or different defense evolution in male versus female guppies (Poecilia reticulata). After 8-12 generations of evolution, guppies were collected from the ancestral (parasite still present) and derived (parasite now absent) populations and bred for two generations in the laboratory to control for non-genetic effects. These F2 guppies were then individually infected with Gyrodactylus and infection dynamics were monitored on each fish. We found that parasite release in nature led to sex-specific evolutionary responses: males did not show much evolution of resistance, whereas females showed the evolution of increased resistance. Given that male guppies in the ancestral population had greater resistance to Gyrodactylus than did females, evolution in the derived populations led to reduction of sexual dimorphism in resistance. We argue that previous selection for high resistance in males constrained (relative to females) further evolution of the trait. We advocate more experiments considering sex-specific evolutionary responses to environmental change

Adding parasites to the guppy-predation story: insights from field surveys

Studies of phenotypic variation in nature often consider only a single potential selective agent. In such cases, it remains an open question as to whether variation attributed to that single measured agent might be influenced by some other unmeasured agent. Previous research has shown that phenotypic variation in the Trinidadian guppy (Poecilia reticulata) is strongly influenced by predation regime, and we here ask whether parasitism might represent an additional important selective agent shaping this variation. We performed a field survey of 26 natural guppy populations of known predation regime in northern Trinidad. We quantified levels of parasitism of guppies by the monogenean ecotoparasite, Gyrodactylus, and examined whether this parasite was associated with guppy body size or male colour. Spatial variation in Gyrodactylus parasitism was consistent between years, and parasite prevalence was generally, but not always, higher at high-predation sites than at low-predation sites. Consistent with previous work, predation regime was related to guppy size and some aspects of male colour, whereas parasitism showed few and only minor associations with the same traits. Moreover, a consideration of parasitism did not alter any interpretations regarding associations between guppy traits and predation regimes. These results suggest that parasitism, at least as quantified in the present study, does not play a major role in shaping variation in guppy body size or colour. Nevertheless, considerable variation in these traits, even within a predation regime, suggests the likely importance of other selective agents beyond just predation regime

Dargentetal.evolsexesJEB

File includes: individual identifier ("identifier"), names of populations used ("pop"), sex of individuals ("sex"), years of field sample ("year"), individuals standard length in mm ("startsl"), type of treatment ("type", i.e. sham or infected=2 G. turnbulli), peak parasite load ("peakpara"), parasite rate of increase r0 ("ro0to10"), outlier status of the individual ("outlier"), relative condition index ("startkn"), death during infection ("died"), and last day in which the individual was counted for parasites ("last count", i.e. day of death)