Hypoplectrus

Abstract: The hamlets (Hypoplectrus) are simultaneously hermaphroditic, carnivorous, largely territorial seabasses (Serranidae), limited almost entirely to the tropical Western Atlantic. Several of the morphospecies in the genus are largely sympatric and syntopic, but morphologically, all are remarkably similar in every major feature except color pattern. Even here, intermediate individuals are occasionally encountered. Hamlets are gleaning predators, and foraging behavior is similar in all observed morphospecies except H. indigo, in which larger individuals were found to feed mostly on the planktivorous pomacentrid Chromis cyaneus. H. indigo also matures at a larger size than other hamlets. Reproductive behavior is similar in all morphospecies. Matings between morphospecies have been observed infrequently and only between morphospecies of most similar color pattern. Overall, the evidence suggests that hamlets form a multispecies complex, with restricted exchange of genes among sympatric morphospecies. The results neither support nor refute the idea that hamlets are aggressive mimics, but they do suggest that at least some of the cases where color patterns of hamlets appear to have converged with those of sympatric noncarnivorous fishes can be accounted for by the operation of similar selective pressures on both putative model and mimic, rather than the occurrence of aggressive mimicry.

Abstract: Because the vast majority of species are well diverged, relatively little is known about the genomic architecture of speciation during the early stages of divergence. Species within recent evolutionary radiations are often minimally diverged from a genomic perspective, and therefore provide rare opportunities to address this question. Here, we leverage the hamlet radiation (Hypoplectrus spp., brightly coloured reef fishes from the tropical western Atlantic) to characterize genomic divergence during the early stages of speciation. Transect surveys and spawning observations in Belize, Honduras and Panama confirm that sympatric barred (H. puella), black (H. nigricans) and butter (H. unicolor) hamlets are phenotypically distinct and reproductively isolated, although hybrid spawnings and individuals with intermediate phenotypes are seen on rare occasions. A survey of approximately 100 000 restriction site-associated SNPs in 126 samples from the three species across the three replicate populations reveals extremely slight genomewide divergence among species (FST = 0.0038), indicating that ecomorphological differences and functional reproductive isolation are maintained in sympatry in a backdrop of extraordinary genomic similarity. Nonetheless, a very small proportion of SNPs (0.05% on average) are identified as FST outliers among sympatric species. Remarkably, a single SNP is identified as an outlier in repeated populations for the same species pair. A minicontig assembled de novo around this SNP falls into the genomic region containing the HoxCa10 and HoxCa11 genes in 10 teleost species, suggesting an important role for Hox gene evolution in this radiation. This finding, if confirmed, would provide a better understanding of the links between micro- and macroevolutionary processes.

Abstract: Large-scale, spatially explicit models of adaptive radiation suggest that the spatial genetic structure within a species sampled early in the evolutionary history of an adaptive radiation might be higher than the genetic differentiation between different species formed during the same radiation over all locations. Here we test this hypothesis with a spatial population genetic analysis of Hypoplectrus coral reef fishes (Serranidae), one of the few potential cases of a recent adaptive radiation documented in the marine realm. Microsatellite analyses of Hypoplectrus puella (barred hamlet) and Hypoplectrus nigricans (black hamlet) from Belize, Panama and Barbados validate the population genetic predictions at the regional scale for H. nigricans despite the potential for high levels of gene flow between populations resulting from the 3-week planktonic larval phase of Hypoplectrus. The results are different for H. puella, which is characterized by significantly lower levels of spatial genetic structure than H. nigricans. An extensive field survey of Hypoplectrus population densities complemented by individual-based simulations shows that the higher abundance and more continuous distribution of H. puella could account for the reduced spatial genetic structure within this species. The genetic and demographic data are also consistent with the hypothesis that H. puella might represent the ancestral form of the Hypoplectrus radiation, and that H. nigricans might have evolved repeatedly from H. puella through ecological speciation. Altogether, spatial genetic analysis within and between Hypoplectrus species indicate that local processes can operate at a regional scale within recent marine adaptive radiations.