EVOLUTIONARY RELATIONSHIPS OF FOUR SPECIES OF HAWAIIAN DROSOPHILA AS MEASURED BY DNA REASSOCIATION

John A. Hunt ¹ and Hampton L. Carson ¹

¹ Department of Genetics, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii 96822

Four species of the Hawaiian Drosophila planitibia subgroup which are homosequential in their polytene chromosomes are resident on the islands of Molokai, Maui and Hawaii. Comparisons of DNA sequence divergence in these four have been made by hybridization of total single-copy radiolabeled tracer DNA from each of the species with excess nonlabeled DNA from each of the species, and measurement of the reduction of average melting temperature (Tma) was made in 2.4 m tetraethyl ammonium chloride. The mean Tma between either D. heteroneura or D. silvestris and either D. planitibia or D. differens was found to be 1.06°, whereas the difference between D. planitibia and D. differens in 0.65° and between D. heteroneura and D. silvestris is 0.75°. These measurements taken together with the distances calculated from isozyme studies, chromosomal relationships, as well as the island locations indicate that the ancestor of these species diverged from other planitibia subgroup flies on Molokai [age 1.8 million years before present, (My BP)]. We hypothesize that one line became the present-day D. differens and diverged probably at the time of formation of East Maui (0.8-1 My BP) to form the species D. planitibia. Flies from the other line migrated to Hawaii soon after its formation (0.7 My BP) to form the two species D. heteroneura and D. silvestris.