THE SALIVARY GLAND CHROMOSOMES OF SEVEN SEGREGATES OF PROSIMULIUM (DIPTERA: SIMULIIDAE) WITH A TRANSFORMED CENTROMERE

Abstract

Preliminary surveys of species of the genus Prosimulium led to the discovery of a group of seven forms characterized by a transformation of the centromere of chromosome I. Samples of six of these forms were received from various parts of Europe and the remaining form is native to Ontario. A detailed cytological analysis was conducted on all seven forms with a view to determining their relationship with each other and with the species whose salivary gland chromosomes carry the standard gene arrangement for the genus Prosimulium.In the band comparisons, it was found that all these forms could be distinguished on the basis of characteristic cytological traits such as fixed rearrangements, floating inversions, and in some cases, specific chromosomal sex-determining mechanisms.Taking the shared, fixed rearrangements as indications of common ancestry, a phylogenetic chart was constructed in which these seven forms were placed in proper relation to one another:P. fontanum standing alone close to the hypothetical ancestor, P. hirtipes, and P. vigintiquaterni forming one line of descent, and P. inflatum and its allies (P. inflatum aff. 1, P. inflatum aff. 2, and P. inflatum aff. 3) forming another.