Alleles underlying larval foraging behaviour regulate adult dispersal in nature

Almost a century ago Joseph Grinnell speculated that the mystery behind bird migration could be unveiled from birds' tendencies to search for prey and forage. Grinnell noticed that individual birds were extremely active on a daily basis and together the distances travelled during these routine behaviours compared easily to a migratory bird's travel during a day's migration. Grinnell argued that movements involving longer distances simply evolved as extensions of movement capacities that birds already poses. This notion might presume that such movements share a common mechanism.

Using fruit flies as a model system we tested this idea by studying dispersal in adult flies known to exhibit a foraging polymorphism as larvae. Rover and sitter phenotypes are natural variants found in the Toronto area. Rovers are active foragers and move greater distances within a food patch than sitter larvae. Rover larvae also move more frequently between food patches than sitter larvae, but when food is absent both phenotypes have similar movement patterns. The gene responsible for this polymorphism is on the second chromosome and is called the foraging gene. Rovers have higher foraging expression levels relative to sitters.

We raised rover and sitter individuals and released them in a large scale field experiment to examine whether rovers were more likely to disperse longer distances in nature than sitter flies. Indeed, rovers were more likely to disperse longer distances than sitter flies and when we examined dispersal in rover flies with decreased expression of the foraging gene we saw that these flies exhibited sitter-like dispersal as well, suggesting that foraging and dispersal share a common genetic mechanism via pleiotropic effects of the foraging gene. We also tested individual flies in simple laboratory assays of dispersal and upregulated foraging gene expression in the brain and neurons of sitter flies. Doing this, we saw that sitters suddenly exhibited rover-like dispersal further implicating the foraging gene in dispersal of fruit flies.

Grinnell might have enjoyed an empirical demonstration of his idea, but I doubt he would have expected it to come from fruit flies. We recently published these results in the journal Ecology Letters.

http://onlinelibrary.wiley.com/doi/10.1111/ele.12234/abstract