Small-scale morphological differentiation in a cichlid may provide clues about rapidly diversifying systems

摘要

The diversification of Lake Malawi cichlid fishes has been characterized as the fastest speciation event within a single vertebrate family. In an effort to understand the population isolation mechanisms that contribute to the diversification of thesecichlids, many researchers are studying population variation (Markert, Danley & Arnegard, 2001) along horizontal (i.e. constant depth) gradients which often include disrupted habitats. Little work, however, has been devoted to investigating population isolation along vertical scales. The vertical cline, in opposition to the horizontal, necessarily introduces gradients in both water pressure and the spectral quality of light (Loew & Mcfarland, 1990). These cichlids, which are able to travel across depths(Hill & Ribbink, 1978), rely heavily on vision for feeding and mate selection (e.g. Jordan et al., 2003). Changes in light may affect behavioural and physiological changes in both feeding and mate selection. Given the predominance of bimodal populationdistributions found along depth gradients in Lake Malawi (Ribbink et al, 1983), investigation into population variation along a vertical axis is warranted.