Mating has opposite effects on male and female sexually selected cuticular hydrocarbons

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

Large Numbers of Matings Give Female Field Crickets a Direct Benefit but not a Genetic Benefit

Female crickets can potentially gain both direct and indirect benefits from mating multiple times with different males. Most studies have only examined the effects of small numbers of matings, although female crickets are capable of mating many times. The goal of this paper is to examine the direct and indirect benefits of mating large numbers of times for female reproductive success. In a previous experiment, female Gryllus vocalis were found to gain diminishing direct benefits from mating large numbers of times. In this study I attempt to determine whether mating large numbers of times yields similar diminishing returns on female indirect benefits. Virgin female Gryllus vocalis crickets were assigned to mate five, ten or 15 times with either the same or different males. Females that mated more times gained direct benefits in terms of laying more eggs and more fertilized eggs. Females that mated with different males rather than mating repeatedly with the same male did not have higher offspring hatching success, a result that is contrary to other published results comparing female reproductive success with repeated versus different partners. These results suggest that females that mate large numbers of times fail to gain additional genetic benefits from doing so

Sex-specific differences in immunological costs of multiple mating in Gryllus vocalis field crickets

Although mating can be costly, most individuals must choose not whether to mate but how many times to mate. This study examined the immunological costs of additional matings once an individual has already mated. Gryllus vocalis field crickets were assigned to mate 5 or 10 times and their immunocompetence probed by measuring their ability to withstand a bacterial challenge by Serratia marcescens, assaying lysozyme-like enzyme activity and phenoloxidase activity, and measuring their success in encapsulating a monofilament implant. Although number of matings generally did not affect the strength of immune responses, females had superior immunity to males in most assays. Females that mated 10 times did, however, have lower lysozyme-like enzyme levels than females that mated 5 times, suggesting that mating can compromise at least one component of female standing immunity. When individuals were allowed to mate ad libitum and their lysozyme-like enzyme activity, phenoloxidase activity, and encapsulation responses measured, there was not a relationship between female mating frequency and lysozyme-like enzyme activity. This result suggests that females may avoid immunological costs of mating by differentially moderating their mating frequency. Copyright 2008, Oxford University Press.

Data from: Crowd control: sex ratio affects sexually selected cuticular hydrocarbons in male Drosophila serrata

Although 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 nonzero 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

data on amino acid composition of spermatophylax

Excel file, variation in amino acid composition of the spermatophylax as a function of inbred line (A-I) and as determined by GC/M

Raw data file info

Raw data file inf

Part2b

Part2

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Part2