PHYLOGENETIC RELATIONSHIPS AMONG DROSOPHILA LONGICORNIS, DROSOPHILA PROPACHUCA AND DROSOPHILA PACHUCA, A TRIAD OF SIBLING SPECIES

Marvin Wasserman ¹ and H. Roberta Koepfer ¹

¹ Department of Biology, Queens College of the City University of New York, Flushing, New York 11367

Drosophila longicornis, D. propachuca and D. pachuca comprise a triad of sibling species. They are morphologically indistinguishable, sympatric forms that, under laboratory conditions, are capable of exchanging genes through the production of fertile F₁ females. However, we have no evidence for introgressive hybridization in nature. The chromosomal constitution of our strains indicates that the ancestral species had the Primitive E gene sequence, and therefore differed from the standard repleta sequence by being Xabc; 2abcg; 3abc. This Primitive E sequence is found in both D. propachuca and D. longicornis. Each of these two species has its own unique rearrangements. D. pachuca is a derived species, which evolved from propachuca. It is cytologically more advanced and has, as its most primitive gene arrangement, one of the more advanced arrangements found in propachuca.