Sibling species of the blackfly Prosimulium onychodactylum (Simuliidae, Diptera): a salivary gland chromosome study

Abstract

Larvae of the morphospecies P. onychodactylum collected from 2 streams in northern Oregon [USA] are divided into 11 sibling species based on fixed and polymorphic inversions. The sibling species have differentiated sex chromosomes; each sibling species falls into 1 of 2 groups based on the chromosome arm which carries the sex chromosome markers. Males exhibit lack of homologous pairing or inversion heterzygosity and females have complete chromosome pairing or inversion homozygosity. There is a succession of sibling species which mature in the streams from Jan. through Sept. Mature larvae of each sibling species are present for .apprx. 6 wk; some are synchronic and others are allochronic. Some of the sibling species occur in the same stream and others are in different streams. Sibling species which are synchronic and sympatric appear to be reproductively isolated. Reproductive isolation may not be complete for sibling species which are normally allopatric or allochronic; small numbers of F1 and backcross hybrids were found between some of these siblings species. The division of the morphospecies into sibling species was also observed in collections from Washington through northern California.