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.

Rouse J ，Watkinson K ，Bretman A 《-》

Plastic responses of male Drosophila melanogaster to the level of sperm competition increase male reproductive fitness.

Bretman A ，Fricke C ，Chapman T 《-》

Exposure to sperm competition risk improves survival of virgin males.

Moatt JP ，Dytham C ，Thom MD 《-》

Sperm production responds to perceived sperm competition risk in male Drosophila melanogaster.

Postcopulatory sexual selection arising from female multiple mating leads to the evolution of ejaculates that maximize a male's reproductive success under sperm competition. Where the risk of sperm competition is variable, optimal fitness may be achieved by plastically altering ejaculate characteristics in response to the prevailing sperm competition environment. In the model species Drosophila melanogaster, males expecting to encounter sperm competition mate for longer and transfer more accessory proteins and sperm. Here we show that after being housed with a single rival for one week, the seminal vesicles of male D. melanogaster contain a significantly greater proportion of live sperm than those of males maintained alone, indicating adaptive adjustment of sperm quality in response to the perceived risk of sperm competition. This effect is due to an increase in the number of live sperm produced, indicating that males upregulate sperm production in response to the presence of rivals. Our data suggest that males show plasticity in the rate of spermatogenesis that is adaptive in the context of a fluctuating sperm competition environment.

Moatt JP ，Dytham C ，Thom MD 《-》

Drosophila melanogaster males increase the number of sperm in their ejaculate when perceiving rival males.

It is common for females from many species to mate with multiple males within one reproductive cycle. As a result, sperm from different males come into contact in the female reproductive organs, where they compete for ova fertilization. This sperm competition appears to drive the ejaculation of a greater number of sperm than required to fertilize the ova. Both models and experimental observations indicate that males adjust the number of sperm in their ejaculate to the presence of rival males. Here, we show that Drosophila melanogaster males increase sperm allocation immediately after perceiving the presence of other males, but not females. Consistent with previous reports, we show that males use both auditory and olfactory modalities to determine the identity of potential rivals in their environment and we further show that these modalities are required for males to modulate sperm allocation. Our results support the sperm competition risk assessment theory, which predicts that males increase sperm allocation while perceiving the immediate risk of sperm competition, and reconcile previous observations in D. melanogaster that were at odds with this model.

Garbaczewska M ，Billeter JC ，Levine JD 《-》