Manmohan D Sharma

Abstract: Female mate choice is one mechanism of sexual selection and provided there is adequate genetic variation in the male traits that are the target of this selection, they will evolve via female choice. Cuticular hydrocarbons (CHCs) are important in <i>Drosophila</i> mate choice, but relatively, little is known about the underlying genetic architecture of CHC profiles in <i>Drosophila simulans</i>. Here, we used gas chromatography–mass spectrometry to investigate patterns of genetic variation in the CHC profiles of male and female <i>D. simulans</i> using isofemale lines. We found substantial genetic variation for CHC profiles and individual CHC components, and individual CHCs were frequently strongly genetically correlated, with a tendency for negative covariance between long- and short-chain CHCs in males. Intersexual genetic covariances were often weak and frequently differed in sign. These findings are novel and significant, highlighting the previously unexplored genetic architecture of CHCs in <i>D. simulans</i> and suggest that this architecture may facilitate sex-specific CHC evolution.

Abstract: Natural and sexual selection are classically thought to oppose one another, and although there is evidence for this, direct experimental demonstrations of this antagonism are largely lacking. Here, we assessed the effects of sexual and natural selection on the evolution of cuticular hydrocarbons (CHCs), a character subject to both modes of selection, inDrosophila simulans. Natural selection and sexual selection were manipulated in a fully factorial design, and after 27 generations of experimental evolution, the responses of male and female CHCs were assessed. The effects of natural and sexual selection differed greatly across the sexes. The responses of female CHCs were generally small, but CHCs evolved predominantly in the direction of natural selection. For males, profiles evolved via sexual and natural selection, as well as through the interaction between the two, with some male CHC components only evolving in the direction of natural selection when sexual selection was relaxed. These results indicate sex-specific responses to selection, and that sexual and natural selection act antagonistically for at least some combinations of CHCs. © 2011 The Author(s).

Abstract: Inbreeding frequently leads to inbreeding depression, a reduction in the trait values of inbred individuals. Inbreeding depression has been documented in sexually selected characters in several taxa, and while there is correlational evidence that male fertility is especially susceptible to inbreeding depression, there have been few direct experimental examinations of this. Here, we assessed inbreeding depression in male fertility and a range of other male fitness correlates in <i>Drosophila simulans</i>. We found that male fertility and attractiveness were especially susceptible to inbreeding depression. Additionally, levels of testicular oxidative stress were significantly elevated in inbred males, although sperm viability did not differ between inbred and outbred males. Copulation duration, induction of oviposition, and the proportion of eggs hatching did not differ for females mated to inbred or outbred males. Nevertheless, our results clearly show that key male fitness components are impaired by inbreeding and provide evidence that aspects of male fertility are especially susceptible to inbreeding depression. © 2010 The Authors. Journal of Evolutionry Biology © 2010 European Society For Evolutionary Biology.

Abstract: There has been recent debate about the expected allometry of sexually-selected traits. Although sexually-selected traits exhibit a diversity of allometric patterns, signalling characters are frequently positively allometric. By contrast, insect genitalia tend to be negatively allometric, although the allometry of nongenital sexually-selected characters in insects is largely unknown (with some notable exceptions). It has also been suggested that there should be a negative association between the asymmetry and size of bilaterally-paired, sexually-selected traits, although this claim is controversial. We assessed the allometry and asymmetry (fluctuating asymmetry, FA) of a nongenital contact-courtship structure, the sex comb, in replicate populations of three species of Drosophila (we also measured wing FA). Sex combs are sexually-selected characters used to grasp the female's abdomen and genitalia and to spread her wings prior to and during copulation. Although species differed in the size of the sex combs, all combs were positively allometric, and comb allometry did not generally differ significantly between species or populations. Comb and wing asymmetry did vary across species, although not across populations of the same species. However, FA was trait specific and was never negatively associated with trait size. © 2011 The Linnean Society of London.

Abstract: Intraspecific variation in a resting metabolic rate (RMR) is likely to be an important determinant of energetic-resource use and may influence the resources subsequently available for allocation to traits not directly associated with somatic maintenance. The influence of RMR on resource availability could be especially important for condition-dependent sexual traits, such as cricket calls, that are themselves energetically costly to produce. RMR may also be associated with longevity, either negatively because individuals with a high RMR burn resources faster and die young, or positively as individuals with high RMR are more able to accrue resources to fuel survival. Additionally, the associations between RMR and other characters may vary across populations if differential selection or drift shapes these traits. Here we tested for differences in RMR, body mass, calling effort, and longevity in two populations of cricket Gryllodes sigillatus and then evaluated the potential influence of RMR on calling and longevity. We find that RMR, calling effort, and longevity varied across populations, but mass did not. Controlling for population and mass, RMR was not significantly associated with calling effort, but was negatively associated with longevity. These findings suggest that male crickets that live fast die young. © 2011 Springer-Verlag.

Abstract: Female mate preference is central to sexual selection, and all indirect benefit models require that there is genetic variation in female preference. This has rarely been tested however, with relatively few studies documenting heritable variation in female preference and even fewer that have directly selected on mate preference to unequivocally show that it can evolve. Additionally, costs of mate preference are poorly understood even though these have implications for preference evolution. We selected on female preference for ebony-males in replicate <i>Drosophila simulans</i> lines, and generated a rapid evolutionary response in both replicates, with the proportion of females mating with ebony-males increasing from approximately 5% to 30% after five generations of selection. This increase was independent of changes in ebony-males as only females were included in our selection regime. We could detect no cost to mate preference itself other than that associated with the fitness consequences of mating with ebony males. © 2010 The Authors. Journal Compilation © 2010 European Society For Evolutionary Biology.

Abstract: The traditional view of sexual selection via female mate choice is that female preference for certain males either has no net fitness cost or is beneficial to overall female fitness. A more contemporary view is that preferred males can at times reduce female fitness. This view has arisen from the realisation that conflict between the sexes is an inevitable feature of sexual reproduction, as each sex necessarily has a different agenda for maximizing fitness. Despite the hailing of sexual conflict as a paradigm shift and its prevalence in the recent sexual selection literature, compelling evidence that attractive males reduce female fitness remains taxonomically restricted. Here we review the findings of a series of investigations into the fitness consequences of female preference in the fly <i>Drosophila simulans</i> and compare them with its sibling species, <i>D. melanogaster</i>. We show that there are stark differences in the fitness consequences of mating with preferred males in the two species and discuss this contrast with reference to the current debates in the sexual selection literature. © 2009 Koninklijke Brill NV.