Sibling species and sex chromosomes in Eusimulium vernum (Diptera: Simuliidae)

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Abstract
The polytene chromosomes of larvae from samples of Eusimulium vernum, E. bicorne, and an undescribed species (designated here as Eusimulium "Yukon") were examined. Twelve cytotypes within E. vernum were distinguished, of which at least eight appear to be good biological species. These cytotypes, together with the two allied morphospecies, were related in a cytophylogeny. An ecological segregation between some of the siblings was observed. One cytotype apparently utilizes two (possibly three) separate chromosome (arms) in sex determination. Five of the total of six chromosome arms are involved in sex determination in the various members of this complex. The genetics of sex determination and the mechanisms of sex-locus shift are discussed in the context of these findings.