Zenobia Lewis

Evidence for strong intralocus sexual conflict in the Indian meal moth, Plodia interpunctella

Males and females share a genome and express many shared phenotypic traits, which are often selected in opposite directions. This generates intralocus sexual conflict that may constrain trait evolution by preventing the sexes from reaching their optimal phenotype. Furthermore, if present across multiple loci, intralocus sexual conflict can result in a gender load that may diminish the benefits of sexual selection and help maintain genetic variation for fitness. Despite the importance of intralocus sexual conflict, surprisingly few empirical studies conclusively demonstrate its operation. We show that the pattern of multivariate selection acting on three sexually dimorphic life‐history traits (development time, body size, and longevity) in the Indian meal moth, Plodia interpunctella, is opposing for the sexes. Moreover, we combined our estimates of selection with the additive genetic variance–covariance matrix (G) to predict the evolutionary response of the life‐history traits in the sexes and showed that the angle between the vector of responses and the vector of sexually antagonistic selection was almost orthogonal at 84.70°. Thus, G biases the predicted response of life‐history traits in the sexes away from the direction of sexually antagonistic selection, confirming the presence of strong intralocus sexual conflict in this species. Despite this, sexual dimorphism has evolved in all of the life‐history traits examined suggesting that mechanism(s) have evolved to resolve this conflict and allow the sexes to reach their life‐history optima. We argue that intralocus sexual conflict is likely to play an important role in the evolution of divergent life‐history strategies between the sexes in this species.

Selfish Genetic Elements Promote Polyandry in a Fly

It is unknown why females mate with multiple males when mating is frequently costly and a single copulation often provides enough sperm to fertilize all a females eggs. One possibility is that remating increases the fitness of offspring, because fertilization success is biased toward the sperm of high-fitness males. We show that female Drosophila pseudoobscura evolved increased remating rates when exposed to the risk of mating with males carrying a deleterious sex ratio–distorting gene that also reduces sperm competitive ability. Because selfish genetic elements that reduce sperm competitive ability are generally associated with low genetic fitness, they may represent a common driver of the evolution of polyandry.

Kin recognition in Drosophila: the importance of ecology and gut microbiota

The animal gut commonly contains a large reservoir of symbiotic microbes. Although these microbes have obvious functions in digestion and immune defence, gut microbes can also affect behaviour. Here, we explore whether gut microbiota has a role in kin recognition. We assessed whether relatedness, familiarity and food eaten during development altered copulation investment in three species of Drosophila with diverse ecologies. We found that a monandrous species exhibited true kin recognition, whereas familiarity determined kin recognition in a species living in dense aggregations. Finally, in a food generalist species, food eaten during development masked kin recognition. The effect of food type on copulation duration, in addition to the removal of this effect via antibiotic treatment, suggests the influence of bacteria associated with the gut. Our results provide the first evidence that varied ecologically determined mechanisms of kin recognition occur in Drosophila, and that gut bacteria are likely to have a key role in these mechanisms.

Effect of Adult Feeding on Male Mating Behaviour in the Butterfly, Bicyclus anynana (Lepidoptera: Nymphalidae)

Many species of lepidopterans supplement their nectar diet with foods rich in nitrogen and minerals, which are present only in trace amounts in nectar. We examined the effect of adult diet on mating behaviour and spermatophore characteristics in male Bicyclus anynana (Butler, 1879) butterflies, which feed on rotten fruits as adults. We found little effect of adult diet on male reproduction in terms of mating rate and sperm production, although males fed on fruit produced larger spermatophores on their first mating compared to males fed sugar only. We also examined how males allocate sperm across matings. Males ejaculate larger spermatophores during their first mating, and produce spermatophores containing decreasingly fewer non-fertile sperm with number of matings performed. Males that produced more non-fertile sperm on their first mating had reduced lifespan possibly indicating a trade-off between sperm production and adult longevity. It is suggested that adult diet has little affect on male ejaculate production and males feed on fruit to supplement their energetic carbon requirements.

Level of sperm competition promotes evolution of male ejaculate allocation patterns in a moth

The risk and intensity of sperm competition can influence male adaptations that ultimately affect male fertilization success, for example investment in sperm production and strategic sperm allocation patterns. Previous studies have examined male behavioural responses to variation in immediate levels of sperm competition. Here we quantified the evolutionary responses of male adaptations resulting from long-term manipulation of the level of sperm competition. By varying the adult sex ratio of populations of the Indian meal moth, Plodia interpunctella, we successfully altered the frequency of male and female copulations, and thus the level of sperm competition experienced by males. As predicted by theory, males evolving under higher levels of sperm competition increased investment in sperm production and differed in their sperm allocation patterns across matings, compared to males evolving under intermediate and low levels of sperm competition. However, we found no evidence for trade-offs between ejaculate components, or between total sperm production and male body size in this species.

Gut microbiota and kin recognition

The animal gut contains a large reservoir of symbionts. Whilst these microbes have obvious physiological functions in, for example, digestion and immune defence, they can also affect their hosts behavior. Increasing evidence suggests that gut microbiota alters the scent of an individual, thereby affecting mate choice and kin recognition.

Sexual and Natural Selection Both Influence Male Genital Evolution

Rapid and divergent evolution of male genital morphology is a conspicuous and general pattern across internally fertilizing animals. Rapid genital evolution is thought to be the result of sexual selection, and the role of natural selection in genital evolution remains controversial. However, natural and sexual selection are believed to act antagonistically on male genital form. We conducted an experimental evolution study to investigate the combined effects of natural and sexual selection on the genital-arch lobes of male Drosophila simulans. Replicate populations were forced to evolve under lifetime monogamy (relaxed sexual selection) or lifetime polyandry (elevated sexual selection) and two temperature regimes, 25°C (relaxed natural selection) or 27°C (elevated natural selection) in a fully factorial design. We found that natural and sexual selection plus their interaction caused genital evolution. Natural selection caused some aspects of genital form to evolve away from their sexually selected shape, whereas natural and sexual selection operated in the same direction for other shape components. Additionally, sexual and natural selection tended to favour larger genitals. Thus we find that the underlying selection driving genital evolution is complex, does not only involve sexual selection, and that natural selection and sexual selection do not always act antagonistically.

Perception of male–male competition influences Drosophila copulation behaviour even in species where females rarely remate

Males in many taxa are known to exhibit behavioural plasticity in response to the perceived intensity of sperm competition, reflected in Drosophila melanogaster by increased copulation duration following prior exposure to a rival. We tested the prediction that males do not adjust their copulation effort in response to the presence of a competitor in Drosophila species where there is little or no sperm competition. Contrary to expectations, male plasticity in copulation duration was found in both Drosophila subobscura and Drosophila acanthoptera, species in which females rarely remate. These results are discussed in relation to the adaptive basis of plasticity in these species.

Remating in the laboratory reflects rates of polyandry in the wild

Much of our understanding of female mating behaviour in insects comes from studies performed under controlled laboratory conditions, with Drosophila as the most commonly used model system. Laboratory studies of Drosophila have demonstrated a strong genetic basis to female remating rate. Because behaviour is strongly influenced by the environment, the heritability of remating rate in laboratory cultures does not necessarily reflect variation that is relevant to field conditions. In this study, we investigated the strength of the link between the behaviour of flies in laboratory and field. Wild-caught female Drosophila pseudoobscura that produced broods sired by multiple males had daughters that remated more rapidly in the laboratory. This suggests that laboratory experiments can successfully reflect differences between females’ mating behaviour in nature.

Sex starved: do resource limited males ensure fertilization success at the expense of precopulatory mating success?

Theory predicts trade-offs between investment in various life history traits, and it is also now generally accepted that reproduction is costly for males. Males must therefore optimize resource allocation across several episodes of reproduction, and this includes investment in both pre- and postcopulatory fitness components. We investigated this in the sperm-polymorphic Indian meal moth, Plodia interpunctella. Resource-limited males were smaller, and had decreased precopulatory mating success, measured as lifetime number of matings. However, they transferred similar numbers of fertile sperm as males reared under high-quality larval conditions, and more nonfertile sperm. By mating less frequently, resource-limited males may allocate sufficient resources to the matings they achieve to ensure fertilization success under sperm competition.