Body shape variation within the Southern Cavefish, Typhlichthys subterraneus (Percopsiformes: Amblyopsidae)

Abstract

The Southern Cavefish, Typhlichthys subterraneus Girard 1859, is one of the most fascinating stygobionts of the Amblyopsidae because of its undescribed diversity. Previous molecular analysis suggests the presence of at least ten distinct lineages in the Southeastern United States. Morphological variation for this group has not been quantified previous to this study. We quantified differences in body shape within the Southern Cavefish utilizing landmark-based geometric morphometrics. We found significant allometry of body shape (Relative Warps) across all putative lineages. We then performed an allometric correction to develop a size-independent morphospace. Principal components analysis indicated that the major axes of size-independent shape explained variation in relative head length to predorsal length, as well as head size and shape in both lateral and dorsal views. We examined if morphological variation corresponded to putative genetic lineages and three geographic variables (aquifer, HUC subregion, and ecoregion). We found shape differences among groups within some variables, but generally, body shape variation was not well explained by these variables. Instead, the dramatic body shape diversity among individuals was explained by ontogeny. Poor agreement between morphology and lineages, as well as multiple geographic variables may be explained by convergent evolution of cave-adapted morphologies or cryptic morphology (i.e., no morphological characters to define diversity).