Comparative skull morphometrics of three sympatric opossums (genus Didelphis)

Abstract

Marsupials of the genus Didelphis are an interesting model to study morphological variation, since they show constant growth throughout their life, and have a wide distribution. Having samples narrowed down in time and space gave us an opportunity to study intra-population variation, therefore having a starting point to study the variability of a species. Our aims are: to analyze the intra-population variation of Didelphis albiventris, Didelphis aurita, and Didelphis marsupialis using specimens collected in the same locality in a short period of time; to compare the variability found in the population of D. albiventris, with the variability of specimens collected in a wide geographic and temporal range (i.e., inter-population variability). We used 2D geometric morphometrics to analyze the skull and mandible of 123 speci- mens. We found a trend where the population of D. albiventris had the lowest Procrustes variance; however, since differences were not large enough to be statistically significant in most of the analyses, our results might be indicating that the three species are morphologically versatile, as suggested by their ability to adapt to different environments. The results obtained for the intra vs. inter population analyses in D. albiventris showed similar levels of morphological disparity in the population from Corrientes Province, including specimens collected throughout a year in the same locality, and in the sample from Uruguay grouping specimens collected throughout 60 years in an entire country. This trend was also observed when comparing the entire D. albiventris sample with both subsamples. These results were unexpected and could be indicating that the population analyzed is highly variable, or that the species as a whole has little morphological variation.