Intraspecific variation in limblessness in vertebrates: A unique example of microevolution

Abstract

The variation in limb reduction in vertebrates has generally been observed as characterizing higher-level taxa. Such structural changes are thus considered to reflect macroevolutionary processes. A statistical analysis of metric variables of some species of the African catfish family, Clariidae, suggests that fin reduction occurs at the microevolutionary level as well. In at least three species of that family intraspecific variation in the presence/absence of the pelvic fins was observed, and one species also showed similar variation for the pectoral fins. Discriminant function analysis confirmed that the variation is intraspecific, and even occurs within the same population. Sexual dimorphism could be excluded. This variation can be observed in the most anguilliform species of the clariid family, suggesting a link with body elongation (as is the case in tetrapods that show limb reduction). Pelvic fin loss appears to precede pectoral fin reduction during evolution. From the morphology it could be ascertained that the loss of the pelvic fins is coupled to the loss of the pelvic girdle, contrary to the case for the pectoral fins and girdle. Differences in functionality may explain this. Breeding results support the occurrence of intraspecific variation, as an F1 offspring showed a difference compared with the parents. For at least one species, the benefit from body elongation and limb reduction can be related to its highly specialized life style, as it lives subterraneanly in muddy soil of the Central African rainforest. © 2002 The Linnean Society of London.