Memory of social experience affects female fecundity via perception of fly deposits.

BACKGROUND: Animals can exhibit remarkable reproductive plasticity in response to their social surroundings, with profound fitness consequences. The presence of same-sex conspecifics can signal current or future expected competition for resources or mates. Plastic responses to elevated sexual competition caused by exposure to same-sex individuals have been well-studied in males. However, much less is known about such plastic responses in females, whether this represents sexual or resource competition, or if it leads to changes in investment in mating behaviour and/or reproduction. Here, we used Drosophila melanogaster to measure the impact of experimentally varying female exposure to other females prior to mating on fecundity before and after mating. We then deployed physical and genetic methods to manipulate the perception of different social cues and sensory pathways and reveal the potential mechanisms involved. RESULTS: The results showed that females maintained in social isolation prior to mating were significantly more likely to retain unfertilised eggs before mating, but to show the opposite and lay significantly more fertilised eggs in the 24h after mating. More than 48h of exposure to other females was necessary for this social memory response to be expressed. Neither olfactory nor visual cues were involved in mediating fecundity plasticity-instead, the relevant cues were perceived through direct contact with the non-egg deposits left behind by other females. CONCLUSIONS: The results demonstrate that females show reproductive plasticity in response to their social surroundings and can carry this memory of their social experience forward through mating. Comparisons of our results with previous work show that the nature of female plastic reproductive responses and the cues they use differ markedly from those of males. The results emphasise the deep divergence in how each sex realises its reproductive success.

Flexible memory controls sperm competition responses in male Drosophila melanogaster.

Males of many species use social cues to predict sperm competition (SC) and tailor their reproductive strategies, such as ejaculate or behavioural investment, accordingly. While these plastic strategies are widespread, the underlying mechanisms remain largely unknown. Plastic behaviour requires individuals to learn and memorize cues associated with environmental change before using this experience to modify behaviour. Drosophila melanogaster respond to an increase in SC threat by extending mating duration after exposure to a rival male. This behaviour shows lag times between environmental change and behavioural response suggestive of acquisition and loss of memory. Considering olfaction is important for a male's ability to assess the SC environment, we hypothesized that an olfactory learning and memory pathway may play a key role in controlling this plastic behaviour. We assessed the role of genes and brain structures known to be involved in learning and memory. We show that SC responses depend on anaesthesia-sensitive memory, specifically the genes rut and amn We also show that the γ lobes of the mushroom bodies are integral to the control of plastic mating behaviour. These results reveal the genetic and neural properties required for reacting to changes in the SC environment.

DDT resistance, epistasis and male fitness in flies.

In Drosophila melanogaster, the DDT resistance allele (DDT-R) is beneficial in the presence of DDT. Interestingly, DDT-R also elevates female fitness in the absence of DDT and existed in populations before DDT use. However, DDT-R did not spread regardless of DDT-independent selective advantages in females. We ask whether sexual antagonism could explain why DDT-R did not spread before pesticide use. We tested pre- and post-copulatory male fitness correlates in two genetic backgrounds into which we backcrossed the DDT-R allele. We found costs to DDT-R that depended on the genetic background in which DDT-R was found and documented strong epistasis between genetic background and DDT-R that influenced male size. Although it remains unclear whether DDT-R is generally sexually antagonistic, or whether the fitness costs noted would be sufficient to retard the spread of DDT-R in the absence of DDT, general fitness advantages to DDT-R in the absence of DDT may be unlikely.

Natural and sexual selection in a wild insect population.

The understanding of natural and sexual selection requires both field and laboratory studies to exploit the advantages and avoid the disadvantages of each approach. However, studies have tended to be polarized among the types of organisms studied, with vertebrates studied in the field and invertebrates in the lab. We used video monitoring combined with DNA profiling of all of the members of a wild population of field crickets across two generations to capture the factors predicting the reproductive success of males and females. The factors that predict a male's success in gaining mates differ from those that predict how many offspring he has. We confirm the fundamental prediction that males vary more in their reproductive success than females, and we find that females as well as males leave more offspring when they mate with more partners.

Female nutritional status determines the magnitude and sign of responses to a male ejaculate signal in Drosophila melanogaster.

Ejaculate chemicals transferred from males to females during mating cause significant changes in female behaviour and physiology, but the causes of phenotypic variation in these responses is little understood. We tested here the effect of adult female nutrition on the response of female Drosophila melanogaster to a specific ejaculate component, the sex peptide (SP), which is of interest because of its effects on female egg laying, sexual receptivity, feeding rate, immune responses and potential role in mediating sexual conflict. We exposed adult females to five different diets and kept them continuously with males that did or did not transfer SP. Diet altered the presence, magnitude and sign of the effects of SP on different phenotypic traits (egg laying, receptivity and lifespan) and different traits responded in different ways. This showed that the set of responses to mating can be uncoupled and can vary independently in different environments. Importantly, diet also significantly affected whether exposure to SP transferring males was beneficial or costly to females, with beneficial effects occurring more often than expected. Hence, the food environment can also shape significantly the strength and direction of selection on mating responses.