The inheritance of geographic variation in body size in the southern brown bandicoot (Isoodon
obesulus) was investigated through a common-environment crossbreeding experiment. The
geographic variation in body size is related to habitat type, suggesting that it may be adaptive.
Adults from two locations in Western Australia, Perth (large animals) and Albany (small
animals), were collected and offspring from both hybrid and non-hybrid matings were reared
under controlled conditions. All four variables examined (head length, pes length, ear length
and body weight) were found to possess a large genetic component, supporting the
interpretation that the geographic variation in size is adaptive. The three length variables
initially showed additive genetic variation, although the variation in body weight displayed
dominance. Genetically controlled differences in growth rate were also detected, with the
smaller animals, found in the relatively poorer environment, possessing the faster intrinsic
growth rate. Thus, not only does there appear to be adaptive divergence in initial body size, but
the countergradient variation in growth rates provides additional evidence for adaptive
divergence in this species.
Evidence of Countergradient Variation in Growth of Spotted Gars from Core and Peripheral Populations
