Lack of mtDNA differentiation among hamlets (Hypoplectrus, Serranidae)

The hamlets are a group of vividly colored fish species of the Serranidae family differentiated only by the color pattern of the body. Although there are divergent views about hamlet taxonomy, experimental and field observations have shown a strong assortative mating, justifying a species status for the different color morphs. Here we analyze the level of evolutionary divergence among six species in respect of mitochondrial DNA, with a view to contrasting the pattern observed with color partitions and previous results obtained with isozymes. The estimated molecular distance among species was low and of the same magnitude as nucleotide diversity within species. Consequently, the net distance and hence the time of divergence between taxa was virtually zero in most comparisons. Although not critically tested, haplotype distribution showed no clear phylogeographic structure, and in many cases the most closely related haplotypes were found at different geographical locations. The absence of differentiated clades between species, based on mitochondrial DNA and isozyme analysis, may have one of two possible origins: a very recent differentiation of species or a lack of absolute barriers to gene flow. However, the available information is insufficient to determine the effect of one or the other, and may require supplementary information from other genes as well as experiments on hybrid fertility. Finally, based on some biological evidence, we suggest that self-fertilization may be an interesting phenomenon to be tested in Hypoplectrus.