Spatially clustered resources increase aggregation and mating duration in Drosophila melanogaster

Abstract

In environments where females mate multiply, males should adjust their behaviour and physiology in response to the prevailing perceived level of sperm competition. This expectation is well supported by both laboratory and field studies, but we dont yet know what mechanisms facilitate these plastic responses in natural populations. One way in which males appear to assess sperm competition risk is through encounter rates with conspecific males. Such encounter rates may be driven by the spatial distribution of resources required by male. However, explicit links between resource distribution, male encounter rate, and shifts in behaviour related to sperm competition have not been demonstrated. Here we show that a small increase in the distance of patches of food resources in the laboratory: (a) approximately halves the mean distances between pairs of males; and (b) is associated with an increase in subsequent copulation duration - previously shown to be a reliable indicator of male perception of sperm competition risk - by more than two minutes. Aggregation of resources, operating via increased encounter rate, is a mechanism that can stimulate plastic male sperm competition responses. Because spatial distribution of resources, including those exploited by Drosophila, is variable in nature, this may explain one way in which sperm competition-related plasticity is influenced in wild-living males.