Movement Ecology: How Genes, Food, and Climate Influence Dispersal in Drosophila melanogaster

Organisms have colonized virtually all types of life-sustaining habitats on our planet resulting in the extraordinary distribution and diversity of life existing today as well as in the past. Elucidating the genetic and environmental contributions to dispersal is important to advance our understanding of how such factors influence the distribution of species and communities. In my thesis, I advanced this understanding by examining adult dispersal in Drosophila melanogaster in strains known to differ in larval foraging behaviour. In the first part of my thesis, I investigated strains of Drosophila melanogaster that are naturally polymorphic in larval foraging behaviour. This polymorphism is mainly due to allelic variation at the foraging (for) locus. forR larvae (rovers) have longer foraging path-lengths compared to fors larvae. In laboratory and field experiments I demonstrated that these strains differ in adult dispersal. Using mutant and transgene fly strains I verified that for was the causal agent contributing to differences in adult dispersal and that for mediates a link between foraging and dispersal via pleiotropy. In the second part, I investigated the effect of habitat loss on connectivity in rovers and sitters. Competing hypotheses propose that connectivity decreases either linearly or nonlinearly with increasing habitat loss. My results support the latter hypothesis. I found critical distances where dispersal and therefore connectivity was reduzed to zero. This critical distance can be manipulated by differentially expressing for in flies suggesting that habitat loss can directly influence genetic variation in populations with multiple dispersal strategies. In the third part of my thesis, I tested whether the distribution of food in landscapes interacted with dispersal. When food was limited rovers and sitters adopted similar strategies to track the distribution of patches, however, when the amount of food increased with the distribution of patches rovers and sitters tracked the distribution of food differently. In the last part of my thesis, I examined how dispersal in flies responded to changes in climate. In a mark-release-recapture experiment I combined capture data with temperature and wind factors in dynamic models to estimate dispersal rates for rovers, sitters and an outbred strain of flies. I found that temperature elicited a similar response in rovers and sitters. This response differed from an outbred strain. I also detected a strong response to wind with wind-advection rates increasing with wind speed for all three fly strains. Surprisingly, my results suggest that response to temperature and wind might minimize known differences in dispersal propensity. My results also strongly suggest that the direction and magnitude of wind may play a key role in the colonization and distribution of fly populations. Taken together, these findings are relevant to the study of the spread of pests and invasive species, particularly in taxa where for might contribute to dispersal. More broadly, my findings have implications for understanding how genes and the environment interact to produce dispersal at the population-level and ultimately the distribution of species and communities.Ph.D