Geometric morphometrics of silky pocket mice (Perognathus: Perognathinae: Rodentia) crania reveals new insights into their variation, evolution, and taxonomy

Abstract

We used cranial geometric morphometric methods (GMM) to explore interspecific variation in Perognathus (silky pocket mice). We digitized 67 cranial landmarks on photographs of 305 adult voucher specimens (10 species and 33 subspecies, 121 localities). After summarizing variation patterns, we explored their association with biological, ecological, and climatic factors, and how (and why) shape evolved through time. Phenotypic clusters did not accord with phylogenetic clades, and we found instances of convergence, divergence, and increased rates of shape change. These are discussed in terms of shared selective pressures (e.g. habitat substrate and burrowing plus historic shifts in habitat/climate and desert adaptation). We also used variation patterns and phenetics to address ongoing taxonomic issues. While pocket mice are difficult to distinguish externally, GMM allowed us to precisely characterize interspecific cranial variation. Species significantly differed and could be classified based on their shape. We find P. alticola to be the most cranially distinct species and suggest raising the P. alticola + P. parvus (including P. mollipilosus) cluster/clade to subgenus status (=Cricetodipus). Cranial GMM found differences among taxa that seemed similar (i.e. cryptic) when previously explored using linear measurements (e.g. P. parvus vs. P. mollipilosus).