Susan N. Gershman’s research while affiliated with The Ohio State University and other places

Animals face many natural challenges, and humans have added to this burden by applying potentially harmful herbicides and unintentionally introducing competitors. We examine the recently introduced Velarifictorus micado Japanese burrowing cricket which shares the same microhabitat and mating season as the native Gryllus pennsylvanicus field cricket. In this study, we assess the combined effects of Roundup (glyphosate-based herbicide) and a lipopolysaccharide (LPS) immune challenge on both crickets. In both species, an immune challenge reduced the numbers of eggs that the female laid; however, this effect was much larger in G. pennsylvanicus. Conversely, Roundup caused both species to increase egg production, potentially representing a terminal investment strategy. When exposed to both an immune challenge and herbicide, G. pennsylvanicus fecundity was harmed more than V. micado fecundity. Furthermore, V. micado females laid significantly more eggs than G. pennsylvanicus, suggesting that introduced V. micado may have a competitive edge in fecundity over native G. pennsylvanicus. LPS and Roundup each had differing effects on male G. pennsylvanicus and V. micado calling effort. Overall, introduced male V. micado spent significantly more time calling than native G. pennsylvanicus, which could potentially facilitate the spread of this introduced species. Despite the population-level spread of introduced V. micado, in our study, this species did not outperform native G. pennsylvanicus in tolerating immune and chemical challenge. Although V. micado appears to possess traits that make this introduced species successful in colonizing new habitats, it may be less successful in traits that would allow it to outcompete a native species.

Crickets face many natural selection pressures, and humans have added to this burden by applying potentially harmful herbicides and unintentionally introducing competitors. We examine recently introduced Velafictorus micado Japanese burrowing crickets which share a microhabitat and season with native Gryllus pennsylvanicus field crickets. In this study, we assess the combined effects of Roundup (glyphosate-based herbicide) and a lipopolysaccharide (LPS) immune challenge on both crickets. In both species, an immune challenge reduced the numbers of eggs that female laid, however, this effect was much larger in G. pennsylvanicus . Conversely, Roundup caused both species to increase egg production, potentially representing a terminal investment strategy. The combined effect of immune challenge and herbicide harmed G. pennsylvanicus fecundity more than V. micado fecundity. Further, V. micado females laid significantly more eggs than G. pennsylvanicus , suggesting that introduced V. micado may have a competitive edge in fecundity over native G. pennsylvanicus . LPS and Roundup each had differing effects on male G. pennsylvanicus and V. micado calling effort. Overall, introduced male V. micado spent significantly more time calling than native G. pennsylvanicus , which could potentially interfere with G. pennsylvanicus mate-location behavior in their shared natural habitat. Despite the population-level spread of introduced V. micad o, in our study, this species did not outperform native G. pennsylvanicus in tolerating immune and chemical challenge. Although V. micado appears to possess traits that make this introduced species successful in colonizing new habitats, it may be less successful in traits that would allow it to outcompete a native species.

Variation in development time can affect life history traits that contribute to fitness. In Gryllus vocalis, a non‐diapausing cricket with variable development time, we used a path analysis approach to determine the causative relationships between parental age, offspring development time and offspring life history traits. Our best‐supported path model included both the effects of parental age and offspring development time on offspring morphological traits. This result suggests that offspring traits are influenced by both variation in acquisition of resources and trade‐offs between traits. We found that crickets with longer development times became larger adults with better phenoloxidase‐based immunity. This is consistent with the hypothesis that crickets must make a trade‐off between developing quickly to avoid predation before reproduction and attaining better immunity and a larger adult body size that provides advantages in male‐male competition, mate choice, and female fecundity. Slower‐developing crickets were also more likely to be short‐winged (unable to disperse by flight). Parental age has opposing direct and indirect effects on the body size of daughters, but when both the direct and indirect effects of parental age are taken into account, younger parents had smaller sons and daughters. This pattern may be attributable to a parental trade‐off between the number and size of eggs produced with younger parents producing more eggs with fewer resources per egg. The relationships between variables in the life history traits of sons and daughters were similar, suggesting that parental age and development time had similar causative effects on male and female life history traits.

In Drosophila serrata flies, there is female choice for male cuticular hydrocarbon (CHC) profiles and male choice for female CHC profiles. Furthermore, both males and females can alter their CHCs: when there is more opportunity for mating, males express combinations of CHCs preferred by females; however, females appear to change CHC profiles to avoid male harassment. In this study, I investigate the effect of number of matings (0–4) on male and female sexually selected CHCs. Mating caused males to express CHCs associated with higher male mating success. Thus, successfully mating males are likely to have increased future mating success. Conversely, females that mated more times expressed CHC profiles that were associated with lower female mating success. Females maximized their offspring production by mating more than once, but additional matings did not provide additional benefits. Furthermore, number of matings did not affect female survival. In total, these results suggest that females alter CHC expression to discourage male courtship when additional matings are not beneficial. In conclusion, plasticity in male and female CHC expression can both increase variance in male mating success and decrease variance in female mating success, driving the evolution of sexually selected chemical signals.

Bed bugs are cited as exemplars of sexual conflict because mating can only occur via traumatic insemination. However, past antagonistic coevolution between the sexes does not necessarily preclude current female choice. Here, we investigate opportunities for precopulatory female choice in bed bugs. We examined whether females seek out mating opportunities when they gain the most benefit: when females are virgin and/or have recently fed. But, we found that female mating and feeding status had little effect on female attraction to males and male odor. To determine whether females approach male harborages (home crevices) to seek matings in nature, we investigated where matings occurred among unfamiliar pairs of bed bugs. We found that, despite female attraction to male odor, matings were most likely to take place in the female's harborage rather than the male's harborage. We also examined the effect of feeding on male and female ability to mate. Whereas previous research reported that engorgement impaired female ability to refuse matings, we found that male feeding status had a larger effect on the success of mating encounters than female feeding status. Fed males had poor mating success, suggesting that males may be faced with a trade‐off between mating and feeding.

While it is advantageous for males to express costly sexually selected signals when females are present, they may also benefit from suppressing these signals to avoid costly interactions with rival males. Cuticular chemical profiles frequently function as insect sexual signals, however, few studies have asked whether males alter these signals in response to their social environment. In Drosophila serrata, an Australian fly, there is sexual selection for a multivariate combination of male cuticular hydrocarbons (CHCs). Here we show that the ratio of females to males that an adult male experiences has a strong effect on his CHC expression, with female-biased adult sex ratios eliciting greater expression of CHC profiles associated with higher male mating success. Classical models predict that male reproductive investment should be highest when there is a small but non-zero number of rivals, but we found that males expressed the most attractive combination of CHCs when there were no rivals. We found that male CHCs were highly sensitive to adult sex ratio, with males expressing higher values of CHC profiles associated with greater mating success as the ratio of females to males increased. Moreover, sex ratio has a stronger effect on male CHC expression than adult density. Finally, we explore whether sex ratio affects the variance among a group of males in their CHC expression, as might be expected if individuals respond differently to a given social environment, but find little effect. Our results reveal that subtle differences in social environment can induce plasticity in male chemical signal expression. This article is protected by copyright. All rights reserved.

The use of cuticular hydrocarbons (CHCs) in species recognition, sex identification and sexual selection is widespread in insects. However, few studies have studied plasticity in CHCs. Here we examine the effect of age and social environment on a suite of sexually selected CHCs in Drosophila serrata. We demonstrate that the combination of CHCs that is associated with increased male mating success (CHCβ) changes as males age, and this effect is mediated by social environment. When single males were housed with multiple females, their expression of CHCβ increased across the first few days of their adult life, after which expression declined with increasing age. In contrast, sexually selected CHCs of males housed with other males, males housed with other males and females, and males housed alone all decreased across days. To determine the long-term consequences of mating on CHC expression, we allowed males a single mating opportunity and subsequently found some indication of a brief spike in CHCβ. Finally, to determine whether visual and olfactory contact with females, copulation, or intromission causes males to express high values of CHCβ, we manipulated male access and physical contact with females. We found that although prolonged copulation causes a slight increase in male CHCβ, only a successful copulation with sperm transfer induced males to develop CHCs associated with high mating success. Taken as a whole, our results demonstrate that the expression of sexually selected CHCs in males varies with both age and social context, and suggest that the latter is mediated at least in part by successful matings with females. More generally, contextual plasticity in CHCs is likely to affect both the experimental design of CHC-based experiments and the evolution of CHC signals as naturally and sexually selected traits.

Indirect genetic benefits derived from female mate choice comprise additive (good genes) and non-additive genetic benefits (genetic compatibility). Although good genes can be revealed by condition-dependent display traits, the mechanism by which compatibility alleles are detected is unclear because evaluation of the genetic similarity of a prospective mate requires the female to assess the genotype of the male and compare it to her own. Cuticular hydrocarbons (CHCs), lipids coating the exoskeleton of most insects, influence female mate choice in a number of species and offer a way for females to assess genetic similarity of prospective mates. Here, we determine whether female mate choice in decorated crickets is based on male CHCs, and whether it is influenced by females' own CHC profiles. We used multivariate selection analysis to estimate the strength and form of selection acting on male CHCs through female mate choice, and employed different measures of multivariate dissimilarity to determine whether a female's preference for male CHCs is based on similarity to her own CHC profile. Female mating preferences were significantly influenced by CHC profiles of males. Male CHC attractiveness was not, however, contingent on the CHC profile of the choosing female, as certain male CHC phenotypes were equally attractive to most females, evidenced by significant linear and stabilizing selection gradients. These results suggest that additive, rather than non-additive genetic benefits accrue to female mate choice, in support of earlier work showing that CHC expression of males, but not females, are condition dependent. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Recent work on Drosophila cuticular hydrocarbons (CHCs) challenges a historical assumption that CHCs in flies are largely invariant. Here, we examine the effect of time of day and social environment on a suite of sexually selected CHCs in Drosophila serrata. We demonstrate that males become more attractive to females during the time of day that flies are most active and when most matings occur, but females become less attractive to males during the same time of day. These opposing temporal changes may reflect differences in selection among the sexes. To evaluate the effect of social environment on male CHC attractiveness, we manipulated male opportunity for mating: male flies were housed either alone, with five females, with five males or with five males and five females. We found that males had the most attractive CHCs when with females, and less attractive CHCs when with competitor males. Social environment mediated how male CHC attractiveness cycled: males housed with females and/or other males showed temporal changes in CHC attractiveness, whereas males housed alone did not. In total, our results demonstrate temporal patterning of male CHCs that is dependent on social environment, and suggest that such changes may be beneficial to males.