Intraspecific morphological variation in the shieldtail snake Rhinophis philippinus (Serpentes: Uropeltidae), with particular reference to tail-shield and cranial 3D geometric morphometrics

Abstract

The Uropeltidae, a family of small, fossorial snakes endemic to south Asia, are characterized by highly modified head and tail morphology. Their secretive nature has led to a dearth of research regarding intraspecific variation in morphology and tail function. Linear morphometrics of external size and shape and scale counts were combined with 3D geometric morphometric analysis of high-resolution computed tomography scans of crania and bony tail-shields to assess intraspecific morphological variation in 35 specimens of Rhinophis philippinus. Cranial and tail-shield shape differences are slight and subtle, though both exhibited significant allometry. Significant sexual dimorphism was found only in numbers of ventral scales, numbers of subcaudal scales, and tail length. There is no evidence of sexual dimorphism in head, cranial or tail-shield shape and size. It is hypothesized that strong functional constraints, induced by head-first burrowing in R. philippinus, have led to strong stabilizing selection in head and cranial shape, with functional constraints outweighing any influence of sexual selection. Lack of tail-shield sexual dimorphism (despite strong tail length dimorphism) suggests a common function in both sexes, likely related to predator avoidance and defense.