Cranial morphometric analyses of the cryptic rodent species Akodon cursor and Akodon montensis (Rodentia, Sigmodontinae)

Akodon cursor and A. montensis are two morphologically cryptic species of Akodontini rodents, undistinguishable by external, skin or qualitative cranial characters. As they can only be separated based on the presence or absence of a gall bladder or by their karyotypes, previously collected individuals in scientific collections that had not these characters annotated cannot be used in any further study with certainty. The purpose of our study was to assess whether geometric morphometrics of the skull and mandible could identify and separate specimens of A. cursor from those of A. montensis. We used 74 adult specimens (48 - A. cursor e 25 - A. montensis) previously identified by their karyotypes, from Southeastern Brazil. We digitized 24, 22, 25, 13 landmarks on images of their skulls (in dorsal, ventral, and lateral views) and mandible, respectively. We assessed size variation (sexual dimorphism and species differences) through t-tests and ANOVAs of centroid sizes of each structure and view, and shape variation through Goodall tests, MANOVAs and Canonical Variants Analyses on Procrustes coordinates. We found significant sexual size dimorphism (p