Genetic divergence and assortative mating between colour morphs of the sea urchinParacentrotus gaimardi

Abstract

Some species of sea urchins feature large variation in pigmentation. This variability may be the result of phenotypic plasticity or it may be associated with genetic divergence between morphs. Paracentrotus gaimardi exhibits five colour morphs (pink, brown, green, grey and black), which often occur side by side on the same rock. We studied genetic divergence between these morphs in three populations on the coast of Brazil. A fragment of the region encoding the mitochondrial ATPase 8 and 6 mitochondrial genes, a fragment of the intron of a nuclear histone and the entire nuclear gene coding for the sperm protein bindin were analysed. Mitochondrial DNA was differentiated between the pink and all other morphs, but the histone intron was similar in all colour morphs. In bindin, nine codons were found to be under positive selection and significant differences of allelic frequencies were observed in almost all pairwise comparisons between colour morphs. Although the molecular differentiation in bindin is not large enough to suggest reproductive isolation, some degree of assortative mating within morphs seems to be occurring in this species.

Oceanic circulation, local upwelling and palaeoclimatic changes linked to the phylogeography of the Cape sea urchin Parechinus angulosus

“…This lack of congruence between the genetic data and the colour morphs is in line with previous echinoid studies (Boissin et al 2008, Vardaro 2010; but see Calderón et al 2010, Binks et al 2011. Since individuals of different colours are often found in the same pools, it seems reasonable to conclude that mating and fertilization between colour morphs is indiscriminate.…”

“…The Cape sea urchin also exhibits unique variation in colour among individuals (pink, purple and red), but there is an apparent random distribution of colour forms throughout the geographic distribution. The latter poses an additional enigmatic layer of complexity when studying the phylogeographic history of this species since evidence exists that urchin colour morphs can show assortative mating (Calderón et al 2010).…”

“…Since assortative mating among colour morphs (see Manier & Palumbi 2008, Calderón et al 2010 can obscure phylogeographic interpretations, we first had to confirm that random mating occurs among the different co-occurring colour morphs at each site. Secondly, we investigated the fine-scale population structure of P. angulosus and hypothesised that this species would display high levels of population connectivity given its larval dispersal ability and abundance.…”

Temporal genetic variability in the Mediterranean common sea urchin Paracentrotus lividus

“…Thus, the study of markers under selection directly implicated in reproductive success can provide a more accurate view of ongoing differentiation processes. A similar result was obtained recently for Paracentrotus gaimardi (Calderón et al 2010), for which comparisons among the different color morphs using different markers revealed contrasting patterns: a nuclear intron revealed no significant differentiation, a mitochondrial gene showed divergence only for a color morph, and bindin provided a strong evidence for differentiation among all morphs.…”

Rates of sea urchin bindin evolution

“…Bindin has been sequenced in 11 genera of sea urchins, but intrageneric variation, which permits insights in the evolution of the molecule, has been studied in only seven: Echinometra (Metz and Palumbi 1996;McCartney and Lessios 2004), Strongylocentrotus (Biermann 1998), Arbacia (Metz et al 1998a), Tripneustes (Zigler and Lessios 2003b), Heliocidaris (Zigler et al 2003), Lytechinus (Zigler and Lessios 2004), and Paracentrotus (Calderon et al 2009(Calderon et al , 2010. Selection on bindin in all of these genera has been studied as the ratio of amino acid replacement to silent substitutions (˘= d N /d S ).…”