Rates of dispersal ofDrosophila pseudoobscuraand its relatives

Abstract

The dispersal behaviour of a species determines to a large extent the gene migration rates among its geographic subdivisions. Gene migration is very important in determining the genetic structure of populations which in turn determines the evolution of the species. The purpose of the work reported here was to obtain quantitative measures of the dispersal behaviour of a well studied insectDrosophila, D. pseudoobscura. Population samples ofD. pseudoobscuraand three related species were collected in nature, dusted with powders that fluoresce under ultraviolet light, and released at a certain point in the same locality where they had been collected. One and 2 days after the release, some of the marked flies were recaptured on baits of fermenting banana, spaced at 20 or 40 m intervals in straight lines on both sides of the release point. There were no significant differences among the four species in their dispersal behaviour. The variance of the distances from the release point to the points at which marked flies were recaptured is used as a measure of the active dispersal of the flies. In nine separate experiments, the average variance for all four species 1 day after the release was 21449 ± 1554 m2, and after two days 27844 ± 3414 m2. The estimated average distance travelled was 192 m after one day and 219 m after 2 days. It appears that the flies disperse faster on the first than on the second day after the release. These results differ in several respects from those obtained in the experiments made in 1942 and 1945.