Natural selection of body size differentiation in spiny mice, Acomys

Tested morphometrics of spiny mice, Acomys, of 181 specimens from 7 localities in Israel and Sinai, to evaluate the factors effecting body size differentiation. These specimens represent 3 karyotypes (2 formal species) comprising 5 populations of Acomys cahirinus (2n = 38); 2 populations of A. cahirinus (2n = 36); and 3 populations of Acomys russatus (2n = 66). Each population of the latter is sympatric with A. cabirinus. The 7 localities represent a general southward transect of increasing aridity. The results indicate that: 1. body characters varied significantly between localities. Body weight and length decreased, whereas tail, ear and relative forefoot and hindfoot lengths generally increased with aridity in accordance with the Bergmann rule. 2. Morphology was found to be partly correlated with allozymic variation.
The geographic patterns and climatic correlates and predictors of morphological variation in Acomys in Israel and Sinai indicate that natural selection, mediated by climatic and biotic factors, is a major cause of body size differentiation. The latter in turn contributes to improving thermoregulatory efficiency and optimizes the energetics balance.