Female-biased spontaneous dispersal in Drosophila melanogaster and sex-specific effect of nutrition and density therein

Dispersal is often essential for attaining Darwinian fitness, especially for species living in spatially structured, heterogeneous habitats. Theoretically, sex-specific resource requirement can drive the two sexes to disperse differently, resulting in sex-biased dispersal (SBD). Understanding ecological factors affecting SBD is important. Using an experimental two-patch dispersal setup, we measured spontaneous dispersal in laboratory-adapted populations of Drosophila melanogaster under a set of common, interlinked ecological scenarios relating to - (a) dietary ecology and (b) adult density. We found that the deteriorating overall nutritional quality of food affects the strength of SBD, and female dispersal is particularly sensitive to the availability of protein. Adult density had a sex-specific effect on dispersal. Female dispersal was found to be density-independent, but males showed increased dispersal at higher densities. Females tend to disperse more from male-biased patches, likely to avoid male harassment, whereas the absence of females drives male dispersal, solidifying mate-finding dispersal hypothesis. This evidence of dispersal suggests that variation in dietary ecology and intraspecific competition can affect the degree and strength of existing SBD, thereby influencing male-female interactions in a patch, and potentially affecting fitness components and population dynamics.