Bergmann’s rule across the Equator: the case of Cerdocyon thous (Carnivora: Canidae)

MARTÍNEZ, PABLO A., MARTI DARDO A., MOLINA WAGNER F. & BIDAU, CLAUDIO J.

La Plata

Jornada; XXIV Jornadas Argentinas de Mastozoología; 2011

Sociedad Argentina para el Estudio de los Mamíferos

One of the first ecological rules is that the largest endothermic animals are found in the coldest climates or highest latitudes. Bergmann’s rule states that this is the result of adaptation to heat conservation (or the avoidance of heat dissipation) by increasing size, thus decreasing area/volume ratio. Aspects of morphological variation in relation to environmental and geographic variables are mostly unknown in South American canids. Cerdocyon thous is a generalist species of wide distribution, occurring from Venezuela to Argentina. In this work we analyzed 302 skulls of adult Cerdocyon thous covering practically all the geographic distribution of the species, using geometric morphometrics. Twenty-seven landmarks were established from photographic images of the dorsal part of the skull. Twenty one historical climatic variables for each location were obtained from the WORLDCLIM database. Multiple regression analyses of log10 centroid size (as an estimator of body size) against environmental and geographic variables were performed in order to analyze size variation throughout the range of the species. Temperature and seasonality variables were shown to have (respectively) highly significant negative and positive correlations with skull size, which is consistent with Bergmann’s rule. However, when individuals north and south of the equator were analyzed separately, both groups showed different size trends. Southern individuals followed Bergmann’s rule while those north of the equator did not show a defined trend.