Systematics and Modes of Reproductive Isolation in the Holarctic Drosophila testacea Species Group (Diptera: Drosophilidae)

Abstract

Reproductive isolation and morphological differences among allopatric populations of the Holarctic species Drosophila testacea v. Roser indicate that this taxon is actually a complex of three morphocryptic species: D. testacea, from Europe and continental Asia; D. orientacea, n.sp., from Japan; and D. neotestacea, n.sp., from North America. Diagnostically important morphological variation is presented, along with distributional data for these three species and D. putrida Sturtevant, the only other member of the testacea species group. Both pre- and postmating barriers to reproduction were observed in various interspecific crosses. Premating isolation is strongly asymmetric between D. testacea and D. neotestacea. Modes of postmating isolation include lack of sperm transfer and failure of hybrid eggs to hatch. The revised taxonomy of this group should facilitate analyses of interesting aspects of the evolutionary ecology of these species.