Dwarf gerbils Gerbillus nanus show now biologically meaningful geographic variation in cranial shape

What is it about?

The dwarf gerbil (Gerbillus nanus) is broadly distributed in Asia, with a range that encompasses altitudinally diverse terrain, including two major mountain ranges. Previous studies have shown this species to be generally varied across its geographic range, both genetically and morphologically. Physical barriers (e.g. mountains) and geographic distance (i.e. isolation by distance [IBD]) is expected to reduce dispersal rates, and consequently could lead to cranial morphological differentiation among populations. Adaptation to local environments is also expected to lead to cranial morphological differentiation among populations. Here, I test these hypotheses by examining variation in cranial shape and size across the geographic distribution of G. nanus using geometric morphometric analysis. Based on a sample of 473 specimens from throughout its distribution, G. nanus populations do not seem to show biologically meaningful variation in cranial shape. Cranial size, on the other hand, did show geographic variation—however, this variation does not seem to show strong patterns of IBD nor adaptation to local environments, which could indicate that the geographic variation in the cranial size of G. nanus populations may be accounted for by factors unexamined in this study.

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Why is it important?

This study is important because it shows that a population of a species could show relatively uniform cranial shape, despite being separated by vast geographic distances. This study also displays the utility of geometric morphometrics in detangling shape from size variation.

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