Effect of environment on skull-size variation in Marmosa robinsoni in Venezuela

Craniometric characteristics of the mouse opossum, Marmosa robinsoni, in Ve nezuela were analyzed with respect to sex, climate, and macrohabitat. We as sessed patterns of phenotypic variation by comparing 6 samples established on the basis of geographic and taxonomic criteria. For most parameters, mal es were larger than females, and there was geographic variation in skull si ze that was not related to geoclimatic factors but to the type of vegetatio n. Specimens inhabiting agricultural lands and disturbed forests were large r than those from cloud and gallery forests; the latter generally was assoc iated with savannas. We suggest that large skull size is related to the hig her productivity of secondary-growth vegetation in anthropogenic areas comp ared with mature forests. We conclude that the specimens studied should be considered as a single subspecies, which corresponds to M. r. robinsoni.