The Significance of Sex-Linked Chromosomal Inversions in the Speciation Process of theSimulium arcticumComplex of Black Flies (Diptera: Simuliidae)

Abstract

ABSTRACT. This study summarizes cytogenetic variation, particularly sex-linked chromosomal inversions which define taxa of the Simulium arcticum complex (Diptera: Simuliidae) in western Montana and portions of northern Idaho, Washington, and Oregon. Variation in polytene chromosomes was determined for nearly 15,000 larvae from 234 collections taken from 58 freshwater sites. The previously described siblings, S. apricarium, S. arcticum sensu stricto, S. brevicercum, and S. saxosum, were most numerous, while all cytotypes, with the exception of IIL-19, were found in low frequency. Additionaly, 6 new cytotypes in low frequency are described. Evidence suggests that the Y chromosome carries the testis-determining gene, and in almost all taxa of S. arcticum, complex paracentric inversions characterize these types. Distributions of (1) S. brevicercum and S. arcticum s. s., (2) S. arcticum s. s. and S. arcticum IIL-18, (3) S. brevicercum and S. arcticum IIL-18, and (4) S. arcticum IIL-9 and S. arcticum IIL-19 hav...