Genomic signatures of host‐associated divergence and adaptation in a coral‐eating snail, Coralliophila violacea (Kiener, 1836)

Abstract

The fluid nature of the ocean, combined with planktonic dispersal of marine larvae, lowers physical barriers to gene flow. However, divergence can still occur despite gene flow if strong selection acts on populations occupying different ecological niches. Here, we examined the population genomics of an ectoparasitic snail, Coralliophila violacea (Kiener 1836), that specializes on Porites corals in the Indo‐Pacific. Previous genetic analyses revealed two sympatric lineages associated with different coral hosts. In this study, we examined the mechanisms promoting and maintaining the snails’ adaptation to their coral hosts. Genome‐wide single nucleotide polymorphism (SNP) data from type II restriction site‐associated DNA (2b‐RAD) sequencing revealed two differentiated clusters of C. violacea that were largely concordant with coral host, consistent with previous genetic results. However, the presence of some admixed genotypes indicates gene flow from one lineage to the other. Combined, these results suggest that differentiation between host‐associated lineages of C. violacea is occurring in the face of ongoing gene flow, requiring strong selection. Indeed, 2.7% of all SNP loci were outlier loci (73/2,718), indicative of divergence with gene flow, driven by adaptation of each C. violacea lineage to their specific coral hosts.

First evidence of a causal link between genetic variation and thermal adaptation in a schistosome host snail

“…The percentage of outliers detected in our study bears resemblance to findings in another study on a marine snail species (Simmonds et al, 2020), with a substantial proportion (26.07%) of these outliers demonstrating potential correlations with temperature, precipitation, or both, illustrating the highly polygenic nature of adaptation to climate. However, the position of these SNPs on the genome could not be determined since no fully assembled reference genome for B. truncatus is available (Young et al, 2022).…”

Host-associated genetic differentiation in the face of ongoing gene flow: ecological speciation in a pathogenic parasite of freshwater fish

“…Recent studies in various host-parasite systems show complex patterns of gene flow and reproductive isolation in parasites (Leder et al, 2021; Momigliano et al, 2017; Simmonds et al, 2020; Teske et al, 2019). These studies highlight the potential influence of disruptive selection in the process of speciation, leading to the divergence of a single ancestral population into groups that specialise in different habitats and hosts.…”

Genomic evidence for contrasting patterns of host‐associated genetic differentiation across shared host‐plant species in leaf‐ and bud‐galling sawflies

“…HAD constitutes the second step in ecological speciation driven by such expansion–restriction cycles, and is thought to arise as a result of contrasting selective pressures acting on traits that influence finding of, or performance on, hosts that differ in their ecological, morphological, physiological or chemical defensive traits (Itami & Craig, 2008; Nosil, 2012). Genetic surveys have revealed frequent HAD in animal parasites (Bell et al, 2018; Galbreath & Hoberg, 2015; Simmonds et al, 2020) and many groups of insect herbivores (Forbes et al, 2017). In the latter, classic examples include apple maggot flies (Hood et al, 2020), yucca moths (Drummond et al, 2010), pea aphids (Peccoud et al, 2009) and goldenrod ball‐gall flies (Stireman 3rd et al, 2005).…”