Ecogeographical rules in the white-eared opossum: <i>Didelphis albiventris</i> has a geographically unstructured generalist phenotype along its distribution

Abstract Patterns of morphometric variation of the skull in several species of mammals can be explained as adaptations to different environmental conditions and availability of food resources, as suggested by Bergmann’s rule and the resource rule hypothesis. A common and widely distributed species, Didelphis albiventris (the white-eared opossum), is an interesting model in which to study such patterns of variation and their ecological determinants. Using geometric morphometrics and a large sample of specimens (N = 185), we studied the relationship between the size and shape of the skull and several environmental variables. We observed a slight tendency for individuals from forested anthropogenic biomes to be smaller, but analyses performed to test for Bergman’s rule and the resource rules were statistically non-significant, and the analysis of the shape variance did not show any clear pattern. These results contrast with the pattern previously described for the species, showing that D. albiventris has a geographically unstructured generalist phenotype, in which the skull size does not follow any ecogeographical pattern, the variance of the skull shape is mostly influenced by size, and the effect of the environmental variables is small.