A systematic revision of genus Isthmomys (Rodentia: Cricetidae)

This study provides data on morphometric variation among allopatric populations of two species of Isthmomys (Hooper & Musser 1964). Cranio-dental measurements and landmark point coordinate data were collected from dorsal, lateral and ventral views of the crania of 126 museum specimens representing the majority of available specimens in the genus. Morphometric techniques were used to examine secondary sexual dimorphism and geographic variation in size and shape within and among OTUs. Statistical analyses revealed negligible sexual dimorphism; therefore both males and females were pooled in the subsequent analyses. A multivariate analysis of variance (MANOVA) of the linear measurements show significant differences (p< .05) between allopatric populations and their respective type localities; corresponding canonical variates and principal component analyses show that the groups are well differentiated. After removing the component of size from the landmark data, principal component analyses of shape and canonical variates analysis showed patterns of shape variation within I. flavidus and I. pirrensis revealing the possibility of polytypic species. Additionally, evaluation of 5 qualitative characters showed unique morphologies for each OUT. Within the context of a systematic revision, these indicate strong possibilities of polytypic species.