| Abstract: | Three species of Drosophila each breed in necrotic tissue of specific columnar cacti endemic to the Sonoran Desert. Drosophila pachea breeds in senita ( Lophocereus schottii) , D. nigrospiracula breeds in saguaro ( Carnegiea gigantea ) or cardón ( Pachycereus pringlei ), and D. mojavensis uses organ pipe ( Stenocereus thurberi ) in Sonora, Mexico and southern Arizona. Patches of these three host cacti have very different spatial distributions, with those of senita being quite frequent and close together, while those of the other hosts are much father apart. Testing all three species simultaneously, we used capture-mark-release-recapture methods to ask if dispersal differed in these species and if differences were those predicted by the spatial availability of the host patches. D. pachea dispersed the shortest distance in all experiments. Furthermore, D. pachea was the only species showing sex-biased dispersal, with male flies exhibiting the greater propensity to disperse. The observations suggest that across similar spatial scales, D. pachea should show greater population genetic structure than the other two species, and that mitochondrial DNA, because of its maternal inheritance, might show greater evidence of structure than nuclear markers. |
