Thus, divergent colour pattern probably contributes to post-mating isolation between the species.
Furthermore, the observation that intraspecific races of H. melpomene show both divergent colour patterns and strong assortative mating implies that mimicry and associated mate preferences are the first steps in divergence in this group [ 13].
Typically, it is the group of songbirds parasitized by cuckoos that has developed the most divergent egg-colour patterns; the group of estrildine finches parasitized by whydahs that has developed particular gape patterns; and among the cleaner wrasses the species Labroides dimidiatus mimicked by the blenny Aspidontus that develops into many different local races.
We propose that the divergent evolution of colour patterns in cave fish presents a candidate trait that provides cave fish in the surface habitats with a disadvantage, for example, in intersexual selection.
However, those polyploids that are not sympatric (on a regional scale) with their progenitor lineages are typically not divergent in floral colour from them, perhaps because of a lack of competition for pollinators.
A negative correlation would support the hypothesis that mating isolation is driven by divergent selection on male colour since foreign males with phenotypes closest to a female's local resident males would have the highest mating success.
Interestingly, neighbouring populations belonging to different colour morphs had highly divergent parasite communities, but neighbouring populations belonging to the same colour morph were also rather divergent in parasitism (with the exception of the light-olive populations - i.e. the only pair without a major barrier to Tropheus dispersal; Figure 1).
The observation of divergent parasite communities between distinct colour morphs suggests that Tropheus represents a good system for parasite-mediated adaptive divergence and speciation.
Previous studies of mitochondrial DNA sequence data revealed polyphyly of the six nominally described species and complex phylogeographic patterns influenced by lake level fluctuations and population admixture, and suggested the parallel evolution of similar colour patterns in divergent evolutionary lineages.
This geographic aid to hybrid identification is further enhanced because the species acting as parents of hybrids consist of as many as 30 very strongly divergent geographic races distinguished by colour pattern.
