Allozyme genetic distances and evolutionary relationships in marsupials ofNorth and South America

Allozyme genetic distances and variability were studied by horizontal starc h gel electrophoresis in 6 species of marsupials from North and South Ameri ca representing 4 different genera. Twenty-one presumptive loci were assess ed in a total of 151 specimens. Only 1 of 21 loci was found to be monomorph ic in the whole sample. Phenetic and cladistic interspecific analysis coinc ided in rendering two sharply differentiated subgroups: one comprising spec ies of the genus Didelphis Linnaeus, 1758 (D. marsupialis Linnaeus, 1758, 1 ). virginiana Kerr, 1792 and D. albiventris Lund, 1840), and the other comp rising Monodelphis dimidiata (Wagner, 1847), Lestodelphys halli (Thomas, 19 21) and Lutreolina crassicaudata (Desmarest, 1804). No relationships betwee n the bradytelic condition, the karyotype stability of this group, and gene tic variability were found. On the other hand, the existence of species wit h brief life span such as Lestodelphys halli and Monodelphis dimidiata (Mar mosini tribe) and species with long life span (Didelphini tribe) allowed us to test the hypothesis which correlates generation-time with genetic varia bility. We conclude that a general explanation for genetic variability must involve more than just generation-time.