Assortative mating as a barrier to gene flow in a coral reef fish species flock

• Main Authors: Barreto, Felipe S., NC DOCKS at The University of North Carolina Wilmington
• Language: English
• Published: 2009
• Subjects: Coral reef fishes > Morphology > Florida > Florida Keys; Coral reef fishes > Variation > Florida > Florida Keys; Coral reef ecology; Antarctic; Pacific; Antarc*
• Online Access: http://libres.uncg.edu/ir/uncw/f/barretof2003-1.pdf

While the only two recognized marine species flocks, the Pacific rockfishes and Antarctic icefishes, show marked morphological distinctions coupled with obscure genetic relationships due to their rapid radiation, the diversification of these flocks is believed to be very ancient (several millions of years before present). In contrast, the hamlets, Caribbean reef fishes of the genus Hypoplectrus (Serranidae), though highly differentiated with respect to their color patterns, do not show monophyletic relationships in mtDNA sequences and are monomorphic in several allozyme loci. Field observations show that mating is strongly assortative with regard to color pattern in sympatric Hypoplectrus species in reefs off Panama and Jamaica. In order to determine the strength of assortative mating and genetic differentiation in natural populations of the previously unstudied Florida Keys Hypoplectrus species, field surveys were conducted at several reefs and Amplified Fragment Length Polymorphisms were assayed in DNA of specimens collected at the study sites. Hamlet populations in the Upper and Middle Keys were composed mainly of blue (H. gemma, 23%) and butter (H. unicolor, 63%) hamlets, with black (H. nigricans) and barred (H. puella) hamlets present at low frequencies. Observation of 68 mating pairs suggested very strong assortative mating, with only mixed pair witnessed. Genetic distances between blue and butter hamlets, estimated from band sharing indeces based on 1108 DNA fragments, resulted in random clustering of individuals, with no monophyly according to color patterns. One AFLP fragment, however, showed strong frequency differences between the two morphospecies. This marker, coupled with the strong assortative mating observed, was regarded as evidence of partial reproductive isolation between H. gemma and H. unicolor. The lack of overall genomic differentiation thus suggested that the radiation of the 11 morphospecies of Hypoplectrus was recent and did not yet reflect species boundaries. The hamlet radiation is a ...