A Geometric Morphometric Analysis of Geographic Mandibular Variation in the Dwarf Gerbil Gerbillus nanus (Gerbillinae, Rodentia).

Previous studies have demonstrated the pliability and adaptability of mammalian mandibles in response to different ecological demands such as food availability. The dwarf gerbil Gerbillus nanus has a wide distribution in Asia in which it encounters varied environments. These varied environments can house different food resources and it would be adaptively advantageous for the opportunistic rodents to have mandibles best suited for the most prevalent food resource. Geometric morphometric analysis was used to test this hypothesis by examining mandibular variation in 436 G. nanus specimens sampled from 44 localities. Based on this sample, mandibular morphology seems to be highly conserved in this species, with both size and shape being non-significantly different between pairs of geographic groups (i.e., locality clusters) and ecoregions. Mandibular size and shape are both not strongly predicted by 48 examined environmental variables. Despite this, the most variable aspect of mandibular shape was associated with its caudal regions, spanning from the coronoid process to the ventral mandibular border. These are regions of temporalis and masseter muscle attachments and thus mandibular variation could be associated with differential (potentially plastic) masticatory adaptations. [ABSTRACT FROM AUTHOR]