Chromosomal Evolution Among North American Microtine Rodents

149 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.Comparative chromosomal analyses among 21 species of New World and one species of Old World microtine rodents were carried out. Species belonged to eight different genera and included 14 species of Microtus. Three differential staining procedures were utilized: C-banding, G-banding, and silver staining. Results of the C-banding analyses indicated that autosomal heterochromatin occurs primarily at centromeric regions, although several species do have long arm interstitial or short arm heterochromatin. There is a general trend among unrelated lineages for a loss in centromeric heterochromatin to occur. Sex chromosomes exhibit a variety of C-banding patterns ranging from being completely euchromatic to having large heterochromatic additions. Ag-NORs were found at three chromosomal locations: centromeric, telomeric, and interstitial. There is extensive intraspecific and interspecific variation in the number and location of NOR sites. A lack of concordance between G-band homology and NOR evolution was observed. NORs were absent from the sex chromosomes. A system was introduced whereby G-banded chromosomes and chromosomal rearrangements were coded quantitatively and phylogenetically analyzed using the PAUP computer program. Three executions of PAUP were conducted where the weights given rearrangements varied. PAUP produced a family of equally parsimonious trees for each analysis necessitating consensus tree construction. Systematically, the analyses support a multitribal arrangement. Dicrostonyx, Neofiber, and Phenacomys were separate from the remaining taxa; and Lagurus and Clethrionomys allied more closely with species of Microtus than with other genera. Although the genus Microtus appeared paraphyletic, two well defined species groups containing 10 of the 14 species emerged. Affinities of the remaining four species are unclear. The importance of euchromatic autosomal rearrangements in descending order is: centric fusion, tandem fusion, pericentric inversions and latent centromeres, deletions, and additions.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD