EVOLUTIONARY GENETICS OF NEW-WORLD TREE SQUIRRELS (TRIBE-SCIURINI)

Protein variation was analyzed electrophoretically in six species of N ew World tree squirrels (tribe Sciurini) representing four of five ext ant genera. Genetic variation was either low (Microsciurus flaviventer -percent polymorphism = 3.7, average individual heterozygosity = 0.031 ) or absent (Sciurillus pusillus) in populations for which samples wer e large enough to permit analysis. Parsimony and locus-by-locus analys es of the protein data supported the close evolutionary affinity of th e genera Sciurus and Microsciurus. A probability analysis of allelic d istribution indicated that Tamiasciurus may be more closely related to the Sciurus-Microsciurus clade than is Sciurillus. This result suppor ts retention of red squirrels, Tamiasciurus, within the assemblage of New World tree squirrels (Sciurini) and indicates that the high level of morphological differentiation seen in Neotropical pygmy squirrels, Sciurillus, is accompanied by a high level of genetic differentiation.