Interdemic variation in the African cyprinidBarbus neumayeri: correlations among hypoxia, morphology, and feeding performance

Abstract

Adaptive change in one character may affect associated, but functionally unrelated, characters in adaptive or nonadaptive ways. For example, adaptive change in gill size (i.e., larger gills in hypoxic habitats) may alter adjacent feeding structures and therefore have indirect effects on feeding behavior. This study examines whether differences in total gill filament length among populations of the African cyprinid Barbus neumayeri correlate with variation in trophic structures and feeding performance. Morphological measurements revealed larger total gill filament length in populations from low-oxygen habitats. Differences in external and internal morphology of the trophic apparatus correlated with those found in gills and suggest a reduction in food capture and processing ability in fish with larger respiratory apparatus. In paired feeding trials on a novel prey type, large-gilled fish spent more time feeding than small-gilled fish of the same body size without ingesting more food. This suggests less efficient food uptake in large-gilled fish from hypoxic habitats. We suggest that variation in gill size facilitates the broad habitat distribution of B. neumayeri but may limit the success of phenotypes crossing physicochemical gradients.