The salivary gland chromosomes of Prosimulium multidentatum Twinn and three forms included in Prosimulium magnum (Dyar and Shannon) (Diptera:Simuliidae)

Abstract

Further study of the morphology of salivary gland chromosome complements within the range described for Prosimulium magnum showed the species to consist of three cytologically distinct populations. The first two forms are without sex chromosomes, (1) a form analogous to the species chromosomal standard, P. magnum, (2) a form which is differentiated by the fixed inversion IIS-25, but (3) the third form has cytological XcYc sex determination. In the Great Lakes region these three forms of the P. magnum complex and P. multidentatum are sympatric in three separate areas, Michigan, Southern Ontario, and Western New York State. Natural hybrids between the forms have so far been obtained only infrequently, and the known hybrids are described. Some chromosomal aspects of speciation are discussed in relation to the present observations on the species complex.