THE SALIVARY GLAND CHROMOSOMES OF SIX CLOSELY RELATED BLACK FLIES NEAR EUSIMULIUM CONGAREENARUM (DIPTERA: SIMULIIDAE)

Abstract

The salivary gland chromosomes of nearctic black flies which form a natural group in Eusimulium close to E. congareenarum were analyzed in detail. Comparisons of their giant chromosome banding patterns disclosed six cytological segregates in two subgroups; subgroup A, with E. innocens, E. anatinum, E. congareenarum, and a cytologically distinct form near the latter designated E. congareenarum 'b'; subgroup B, with E. excisum and E. rivuli. Within each subgroup closely related species differ at least by (1) two or three interspecific inversions, (2) the intraspecific specific inversions present, and (3) the details of the X and Y chromosomes. The differences between the subgroups include (1) the position of the nucleolus, (2) the identity of the sex chromosomes as either the first or third pair, and (3) about 15 interspecific inversions between E. congareenarum and E. excisum, the most closely related species from either subgroup. The phylogenetic interrelationships have been traced by means of the interspecific inversions.