Morphologic Variation and Hybridization in Myotis yumanensis sociabilis and Myotis lucifugus carissima

Abstract

Morphologic variation was examined in 240 Myotis yumanensis sociabilis and 169 Myotis lucifugus carissima from northeastern California and southcentral Oregon to determine whether extreme similarity was due to intraspecific variation or to hybridization. Seven external and eight cranial variables were analyzed using multi-variate discriminant analyses. Intraspecific variation is partially responsible for mensurable overlap, so that forearm length and greatest length of skull do not differentiate large M. y. sociabilis from small M. l. carissima . Pelage color and skull profile also fail to distinguish some individuals. Morphologically intermediate individuals were found in roosts shared by both species. Two multivariate analyses showed condylo-premaxillary length to be the best discriminating character although separation of the two species by this character alone was poor. Limited hybridization is probably occurring in the area from which I obtained specimens. Eleven animals were classified as hybrids based on statistical probabilities. The probable explanation for hybridization is the relatively recent establishment of sympatry between the two species following Pleistocene climatic events. Some morphologic convergence may be the result of a greater degree of ecologie similarity in this area of sympatry. Because intraspecific variation complicates identification of pure parental types as well as hybrids, it is impossible to verify introgression by using statistical methods. The current status of the two species in other parts of their ranges suggests introgression is not occurring. The taxonomic history of M. yumanensis and M. lucifugus is reviewed.