Ontogenetic shifts in phenotype–environment associations in N ile perch, L ates niloticus ( P erciformes: L atidae) from L ake N abugabo, U ganda

Habitat‐associated trait divergence may vary across ontogeny if there are strong size‐related shifts in selection pressures. We quantified patterns of phenotypic divergence in N ile perch ( L ates niloticus ) from ecologically distinct wetland edge and forest edge habitats in L ake N abugabo, U ganda, and we compared patterns of divergence across three size classes to determine whether trends are consistent through N ile perch ontogeny. We predicted that inter‐habitat variation in biotic (e.g. vegetation structure) and abiotic (e.g. dissolved oxygen concentration) variables may create divergent selective regimes. We compared body morphology using geometric morphometrics and found substantial differences between habitats, although not all trends were consistent across size classes. The most striking aspects of divergence in small N ile perch were in mouth orientation, head size, and development of the caudal region. Medium‐sized N ile perch also showed differences in mouth orientation. Differences in large individuals were related to eye size and orientation, as well as caudal length. The observed patterns of divergence are consistent with functional morphological predictions for fish across divergent trophic regimes, high and low predation environments, and complex and simple habitats. Although this suggests adaptive divergence, the source of phenotypic variation is unknown and may reflect phenotypic plasticity and/or genetic differences. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society , 2013, 110 , 449–465.