Genetic mosaic in a marine species flock

Abstract

We used molecular approaches to study the status of speciation in coral reef fishes known as hamlets (Serranidae: Hypoplectrus). Several hamlet morphospecies coexist on Caribbean reefs, and mate assortatively with respect to their strikingly distinct colour patterns. We provide evidence that, genetically, the hamlets display characteristics common in species flocks on land and in freshwaters. Substitutions within two mitochondrial DNA (mtDNA) protein-coding genes place hamlets within a monophyletic group relative to members of two related genera (Serranus and Diplectrum), and establish that the hamlet radiation must have been very recent. mtDNA distances separating hamlet morphospecies were slight (0.6 ± 0.04%), yielding a coalescent estimate for the age of the hamlet flock of approximately 430 000 years. Morphospecies did not sort into distinct mtDNA haplotype phylogroups, and alíeles at five hypervariable microsatellite loci were shared broadly across species boundaries. None the less, molecular variation was not distributed at random. Analyses of mtDNA haplotype frequencies and nested clades in haplotype networks revealed significant genetic differences between geographical regions and among colour morphospecies. We also observed significant microsatellite differentiation between geographical regions and in Puerto Rico, among colour morphospecies; the latter providing evidence for reproductive isolation between colour morphospecies at this locale. In our Panama collection, however, colour morphospecies were mostly genetically indistinguishable. This mosaic pattern of DNA differentiation implies a complex interaction between population history, mating behaviour and geography and suggests that porous boundaries separate species in this flock of brilliantly coloured coral reef fishes.

Population genetic structure, coloration, and morphometrics of yellowhead jawfish Opistognathus aurifrons (Perciformes: Opistognathidae) in the Caribbean region

“…Hamlets Hypoplectrus spp. exhibit distinct color morphs and are known to mate assortatively (Puebla et al 2007), although mitochondrially, Hypoplectrus are unresolved and suggestive of recent speciation (McCartney et al 2003, Ramon et al 2003. If observed patterning differences observed in O. aurifrons do serve as mate recognition characters, then it is probable that polymorphisms in genes controlling patterning are driving phenotypic differences, even though mitochondrial loci were incompletely sorted (Palumbi et al 2001, Avise 2004.…”

“…However, a series of studies on hamlets Hypoplectrus spp. found that even in the presence of assortative mating among many drastically different color forms, genetic struc turing is weak or almost completely absent (McCartney et al 2003, Ramon et al 2003, Puebla et al 2007.…”

Molecular evidence of intraspecific variability in Lysidice ninetta (Polychaeta: Eunicidae) in the Mediterranean Sea

“…Strong genetic variability associated with both colour and sexual strategy have been found in different fishes (McCartney et al 2003). Among marine invertebrate species, studies of ascidians have pointed out discordant results.…”

Stable isotope analysis of the Hypoplectrus species complex reveals no evidence for dietary niche divergence

“…Bierne et al 2003). Coral reef fish of the genus Hypoplectrus (hamlets), which have attracted increased attention in recent years (McCartney et al 2003, Ramon et al 2003, Puebla et al 2007, provide an ideal model for studying the speciation mechanisms of a polymorphic group with high geographic genetic connectivity within the expansive marine environment.…”

“…Hamlets show very strong assortative mating preferences for their own colour morph (Domeier 1994, Puebla et al 2007. Despite this fact, there are few clear genetic distinctions between morphs (McCartney et al 2003), which suggests recent morph diversification.…”