Recurrent Body Shape Patterns in Cave- and Surface-Dwelling Trichomycterid Catfishes.

The evolution of body shape in animals reflects the interplay between functional constraints and habitat structure. While cave environments are well known to promote regressive traits in fish such as eye and pigment loss, their influence on overall body form remains poorly understood. Here, we examine patterns of body shape variation in cave-dwelling and surface-dwelling trichomycterid catfishes from northeastern Colombia to assess whether consistent associations exist between habitat type and morphology. Using geometric morphometric analyses, we quantified differences in body shape among species inhabiting subterranean and surface environments. Our results reveal significant habitat-associated differentiation in body shape along the main axes of morphological variation, despite some overlap indicating that habitat does not fully predict morphological variation. Cave-dwelling species exhibit more elongated and fusiform body shapes, whereas surface-dwelling species tend to have deeper and more robust morphologies. These patterns are consistent with differences in habitat-associated ecological conditions, although no direct functional or performance data were evaluated. The recurrence of similar body shapes among species from different clades occupying comparable habitats is consistent with repeated morphological responses to shared ecological constraints.