Description and Evolutionary Relationships of Two Species of the Drosophila mulleri Cluster (Diptera: Drosophilidae)

Abstract

Drosophila huaylasi Pla & Fontdevila, n. sp., and Drosophila nigrodumosa Wasserman & Fontdevila, n. sp., are members of the D. mulleri cluster ( D. mulleri complex) of the D. repleta species group. They are described here using morphological, reproductive, chromosomal, and genetic (allozymic) characters. Morphology of the male genitalia is a distinctive, but not unique, characteristic. All the described D. mulleri cluster species are homosequential, there being no variability in the polytene chromosomes. The metaphase chromosomes show minor interspecific differentiation in the length of the sex chromosomes. Allozyme differentiation is more informative and shows that D. huaylasi and D. nigrodumosa are closely related to each other. They are much closer to D. mulleri than to D. aldrichi . Postzygotic reproductive isolation is complete between either D. huaylasi or D. nigrodumosa and D. aldrichi , which accords with their genetic differentiation. On the other hand, in laboratory crosses with no choice, some interspecific gene exchange is possible among D. mulleri, D. huaylasi , and D. nigrodumosa , through backcrosses of fertile F1 hybrid females. However, the three species appear to be allopatric and presumably no gene flow exists in nature.