Long-Distance Migration of Drosophila. 2. Presence in Desolate Sites and Dispersal Near a Desert Oasis

The striking genetic uniformity of apparently isolated Drosophila populations has led to the hypothesis that they are connected by occasional long-distance migration. We investigated dispersal of three Drosophila species in the desert of Death Valley, California, by seeking flies in desert locations far from apparent breeding sites and by monitoring the movement of flies released at various distances from a large oasis. During the spring, we caught D. pseudoobscura in many remote desert locations as far as 26 km from the nearest likely breeding site. Because flies cannot be found at these sites in the middle of summer, they probably fly long distances to get there. We also released marked D. pseudoobscura, D. melanogaster, and D. simulans near a large oasis in Death Valley in order to study their ability to return to a favorable habitat from various distances. These flies were more likely to be recaptured toward the oasis when released within 30 m of it, but not when released beyond 100 m. Flies occurred naturally in appreciable numbers beyond this 100-m "attractive radius." These observations suggest that haphazard dispersal from oases may sometimes place flies in adjacent desert from which they do not return. When coupled with previous observations that flies released in the desert may move many kilometers to oases, that flies can rapidly disperse between distant oases, and that flies are frequently found in open desert many miles from probable breeding sites, our release results support the likelihood of substantial long-distance migration between desert populations of Drosophila.