Abstract Phenotypic variation can assume multiple forms including sexual dimorphism, geographic and subspecific differences, or morphological clines along environmental gradients. Importantly, these sources of variation may interact, especially across large spatial and/or temporal extents. Moreover, subspecies delineations are often based on discontinuities in phenotypic variation thought to represent distinct populations. We examined phenotypic variation within Myotis velifer, a bat species distributed across the southwestern United States and Mexico to Honduras. We measured a series of cranial characters from 195 specimens from 98 sites of the 3 currently recognized subspecies (M. v. incautus, M. v. magnamolaris, and M. v. velifer) to identify potential differences among sexes and subspecies. We also used multivariate analyses to relate variation in cranial characteristics to spatial and environmental gradients. We found significant differences in cranial characters among subspecies, but no differences between sexes and no sex-by-subspecies interactions. We also demonstrated that spatial gradients but not subspecies designation or sex explained significant unique variation in cranial morphology. Climatic gradients were primarily characterized by larger phenotypes in environments with more variable temperatures. Results from this work question existing subspecific designations for this species as well as demonstrate the importance of accounting for geographic clines when examining phenotypic variation in the context of subspecific delineation.
Newman et al. (2026) studied this question.