A Cytological Description of the Simulium arcticum Complex (Diptera: Simuliidae) of Central Montana: Sibling Species Status

Abstract

Polytene chromosomes of black flies, (Diptera: Simuliidae), were studied at Little Prickly Pear Creek (LLPC), Lewis and Clark County, Montana during the summer of 2000. Larvae from the LPPC were predominantly Simulium arcticum until July when they were replaced by S. vittatum. Analysis of 37 larvae (18 male and 19 female) from LPPC (May 17) revealed the presence of two sibling species of S. arcticum (IIL-3 and IIL-7) differentiated on the basis of the variant banding patterns in both sex determining and autosomal segments of the larval polytene chromosomes. Males of both siblings are heterozygous for unique inversions observed at the base of chromosome II-L whereas females of both siblings possess the standard (non-inverted) sequence. Additionally, the IIS-11 autosomal inversion is standard (St St) in the IIL-3 sibling while being fixed (Inv. Inv.) in the IIL-7 sibling; further, no hybrids were observed. The presence of two unique sibling species of S. arcticum identified at LPPC and the absence of hybrids between the two documents reproductive isolation in sympatry. These results suggest that central Montana may be rich in diversity of sibling species of black flies thus encouraging further study.