Defining the Cytotype and Persistence Concepts in Black Flies (Diptera: Simuliidae)

Abstract

Y-linked chromosomal inversions promote reproductive isolation in black flies. Time to fixation to total sex-linkage varies among incipient species. Persistence from year-to-year of chromosome types at any location is largely unstudied. Therefore, I analyzed the polytene chromosomes of a large sample (n = 800) of black fly larvae of the Simulium arcticum complex from the Little Blackfoot River (LBR) in western Montana to determine: 1) the extent of linkage of inversions to the Y chromosome and 2) persistence of taxa from year-to-year and compared these data to those of previous analyses, which were based on smaller sample sizes. I hypothesized that the large sample in 2011 would support previous observations. Thirteen Y chromosome types were described in 2011, whereas only nine types had been described previously. This study suggests that the IIL-10, IIL-18, IIL-38, and IIL-51 inversions are Y-linked at the LBR and that they chromosomally define cytotypes (taxa diverging from a common ancestor), which deserve more detailed study. Moreover, persistence was observed since all previous inversions, with the exception of IIL-30, IIL-35, and IIL-84 were found in 2011.