Temporal variation in skull size and shape in the southern brown bandicoot, Isoodon obesulus (Peramelidae: Marsupialia) in Western Australia

Isoodon obesulus exhibits geographic variation in body size and shape, which appears to be adaptive. The geographic range of this species is declining, so the presence of adaptive divergence is of concern for the conservation of this species, both in the long term (loss of diversity decreasing evolutionary potential) and short term (choice of source populations for translocations). In this study, skulls of I. obesulus, both recent (animals alive within the last 100 years) and fossil (a few thousand years old), were examined and a range of measurements obtained. Comparisons were made between the two data sets to see whether skull morphology has changed over this relatively short period. Such a change may indicate rapid evolution of these characters and therefore the potential for fast regeneration of any lost geographic variation. Fossil skulls were smaller than their recent counterparts, had shorter 'snouts' relative to skull width and depth, and displayed no geographic variation in size and shape, whereas recent skulls were geographically differentiated. Because of the apparent rapid evolution in these characters, the implications of adaptive variation in size and shape in I. obesulus with regard to its conservation may be strictly short term, since any geographic variation lost may be quickly recovered if suitable conditions exist.