Variation in vertebral number and its morphological implication in Galaxias platei

Abstract

The vertebral number is a major trait of fish structure, related to swimming, feeding, and predator avoidance. The `puyen grande´ Galaxias platei, a big size species of the Galaxiidae family, is a fresh water benthic fish widely distributed in the Andean lakes of southern Chile and Argentina. This species has one of the highest within-species vertebral range (50-62) among the family and shows a noticeable polymorphism that can be related to diet and predation risk. Our results shows that mean vertebral number (MVN) increase towards high latitude, i.e. Jordan´s rule apply to this species. However, due to the wide geographic variation of the species not only in latitude but also in altitude, the most explicative variable for MVN was the mean winter air temperature (a negative dependence). Morphological data suggest that the increment in the vertebral number would be in the pre-pelvic region of the trunk and in the caudal region, but not in the segment bounded between the pelvic fin insertion and the anus. Vertebral number have strong implications in hydrodynamics and swimming performance. Hence, vertebral number variation in G. platei has implication in fitness at both individual and population levels.