Genomic landscape of geographically structured colour polymorphism in a temperate marine fish

Abstract

The study of phenotypic variation patterns among populations is fundamental to elucidate the drivers of evolutionary processes. Empirical evidence that supports ongoing genetic divergence associated with phenotypic variation remains very limited for marine species where larval dispersal is a common homogenizing force. We present a genome‐wide analysis of a marine fish, Labrus bergylta, comprising 144 samples distributed from Norway to Spain, a large geographical area that harbours a gradient of phenotypic differentiation. We analysed 39,602 biallelic single nucleotide polymorphisms and found a clear latitudinal gradient of genomic differentiation strongly correlated with the variation in phenotypic morph frequencies observed across the North Atlantic. We also detected a strong association between the latitude and the number of loci that appear to be under divergent selection, which increased with differences in coloration but not with overall genetic differentiation. Our results demonstrate that strong reproductive isolation is occurring between sympatric colour morphs of L. bergylta found at the southern areas and provide important new insights into the genomic changes shaping early stages of differentiation that might precede speciation with gene flow.

Distinct genetic clustering in the weakly differentiated polar cod, Boreogadus saida Lepechin, 1774 from East Siberian Sea to Svalbard

“…Clustering could involve phenotypically distinct morphotypes as in ballan wrasse, Labrus bergylta, where spotty and plain morphs displaying genetic differentiation (Quintela 2016) occur in sympatry (Villegas-Ríos et al 2013b). The duration and the timing of the spawning season coincide despite their differences in life-history strategies (Villegas-Ríos et al 2013a); therefore, body colour has been invoked to play a pivotal role in facilitating sympatric speciation in the absence of impermeable geographic barriers (Casas et al 2021). In contrast, for other fish species, time of spawning seems to be a crucial evolutionary driver.…”

Genetic structure, UV‐vision, wing coloration and size coincide with colour polymorphism in Fabriciana adippe butterflies

“…The existence of distinct and (partially) genetically diverged colour morphs in a species has previously been interpreted as a sign of reproductive isolation (e.g. Boratynski et al., 2014; Casas et al., 2021), which can be mediated through assortative mating, or as a result of spatial sorting (Van Belleghem et al., 2016). If morphs utilize different habitats, assortative mating may occur as a by‐product even in the absence of specific mate preferences or avoidance behaviours (Berggren et al., 2012; Calderon et al., 2010; Shine et al., 2011).…”

Multispecies colour polymorphisms associated with contrasting microhabitats in two Mediterranean wrasse radiations

“…Recent research focusing on the ballan wrasse ( Labrus bergylta ) revealed genome‐wide differentiation between sympatric plain and spotted morphs in some parts of the distribution range, consistent with early stage speciation (Casas et al, 2021; Quintela et al, 2016). Although no study has investigated genomic differences between green and brown morphs in wrasses so far, aquarium experiments by Arigoni et al (2002) showed that the CP in Symphodus ocellatus and Symphodus roissali is plastic to some extent with colour changes within several weeks to months, but not plastic in Symphodus rostratus .…”

“…Recent research focusing on the ballan wrasse (Labrus bergylta) revealed genome-wide differentiation between sympatric plain and spotted morphs in some parts of the distribution range, consistent with early stage speciation (Casas et al, 2021;Quintela et al, 2016).…”