CONICET | Buscador de Institutos y Recursos Humanos

Polydolopidae is a family of Paleogene marsupials, recorded in Southern South America (Patagonia in Argentina, Central Chile) and the Antarctic Peninsula (in Marambio/Seymour Island)(Marshall, 1982; Woodburne and Zinsmeister, 1984). Two localities with polydolopids have been dated and are almost synchrounous: Laguna Fría (Ignimbrita Barda Colorada Formation; Tejedor et al., 2009), in the vicinities of Paso del Sapo (Chubut Province, Argentina) and Marambio/Seymour Island (Cucullaea IAllomember, La Meseta Formation; Antarctic Peninsula; Chornogubsky et al., 2009). Preliminary results suggest an adjustment of the polydolopid body mass to the Bergmann Rule. Here we analyze the body mass of these marsupials in a phylogenetic framework. A phylogenetic comparative method (Phylogenetic Eigenvector Regression) was applied to detect the phylogenetic signal on the body mass data. A principal coordinate analysis was performed on the double-centered phylogenetic distance matrix in order to extract the significant eigenvectors. These eigenvectors that summarize the phylogenetic relationship amongst species were used as independent variables versus body mass in a multivariate regression. The residual portion of this regression represents the amount of variation independent from the phylogenetic structure. The first two axis explain the 92,11% of the variability in the phylogenetic distances. Regression analysis of body mass on these two eigenvectors was significant (F=8,356; p=0,002), with an R2 equal to 0.443. According to PVR the 44% of the body mass variation of polydolopids would be explained by phylogenetic inertia. The plot of detransformed residuals shows the same pattern that the single analysis of body mass. The species of Antartica have higher body masses than their Patagonian counterparts. So the adjustment to Bergmann Rule is maintained after removing the phylogenetic trends.