Color-based association among heterospecifics in lake Malawi rock-dwelling cichlids

Female mate choice can be an imperfect barrier against hybridization. Among the cichlid fishes of the East African great lakes, sexual selection on male nuptial coloration has been noted as being particularly important for reproductive isolation among closely related lineages. Diversification of the rock-dwelling cichlids of Lake Malawi has led to a repeating pattern of color morphs wherein more distantly related species may look more similar than a more closely related pair. Using members of the Metriaclima zebra group and a heterogener, I tested the hypothesis that females would spend greater time associating with males more similarly colored to her species than females would with divergently colored, although more closely related males. Experimental results were consistent with this hypothesis, thus supporting the speculation and some field observation that mate choice can fail as a barrier to hybridization if a female encounters a distantly related male that shares the nuptial coloration of males of her own species and color morph. This notion is discussed in the broader context of both the adaptive and non-adaptive mechanisms that have been suggested to be important to the radiation of this group.