How robust are the patterns of density-dependence and sex-bias in dispersal?

Organisms disperse from one place to another for a variety of reasons, including search for food or mates and escape from stress. One of the factors that influence dispersal is population density. We investigated three issues on the effects of population density on dispersal, namely (a) How consistent are patterns of density-dependent dispersal across environments? (b) What happens when males and females react differently to changes in population density? (c) Do asymmetric responses to density in males and females modulate sex-biased dispersal? To address these questions, we assayed the dispersal ~34,200 fruit flies under various combinations of density and environments in three independent experiments.

We demonstrate that the presence or absence of density-dependent dispersal is heavily dependent on the pre-dispersal environmental context. In addition, males and females exhibited (negative) density-dependent dispersal when they dispersed together, but not when they dispersed separately. More interestingly, under an appropriate set of conditions, the direction of dispersal switched from male-biased to female-biased. We propose a hypothesis based on male mate harm for a mechanistic explanation of these results. Together, our results emphasize the plasticity of both density dependence and sex bias in dispersal.

The authors through Sutirth Dey
 

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