Fine-scale seascape genomics of an exploited marine species, the common cockle Cerastoderma edule, using a multimodelling approach.

Ilaria Coscia,Alice Goward-Brown,Enda O'Dea,Sophie B Wilmes,Allan D Mcdevitt,Shelagh K Malham,Peter E Robins,Joseph E Ironside

doi:10.1111/eva.12932

Abstract

Population dynamics of marine species that are sessile as adults are driven by oceanographic dispersal of larvae from spawning to nursery grounds. This is mediated by life‐history traits such as the timing and frequency of spawning, larval behaviour and duration, and settlement success. Here, we use 1725 single nucleotide polymorphisms (SNPs) to study the fine‐scale spatial genetic structure in the commercially important cockle species Cerastoderma edule and compare it to environmental variables and current‐mediated larval dispersal within a modelling framework. Hydrodynamic modelling employing the NEMO Atlantic Margin Model (AMM15) was used to simulate larval transport and estimate connectivity between populations during spawning months (April–September), factoring in larval duration and interannual variability of ocean currents. Results at neutral loci reveal the existence of three separate genetic clusters (mean F ST = 0.021) within a relatively fine spatial scale in the north‐west Atlantic. Environmental association analysis indicates that oceanographic currents and geographic proximity explain over 20% of the variance observed at neutral loci, while genetic variance (71%) at outlier loci was explained by sea surface temperature extremes. These results fill an important knowledge gap in the management of a commercially important and overexploited species, bringing us closer to understanding the role of larval dispersal in connecting populations at a fine geographic scale.

Highlights

The assumption that genetic homogeneity predominates in marine organisms due to the lack of physical barriers and high dispersal potential at all life stages has been challenged in recent years (Allendorf, 2017)
Environmental association analysis indicates that oceanographic currents and geographic proximity explain over 20% of the variance observed at neutral loci, while genetic variance (71%) at outlier loci was explained by sea surface temperature extremes
A panel of 1,725 single nucleotide polymorphisms (SNPs) markers were analysed in relation to sea temperature and oceanographic currents, environmental variables that have been shown to be drivers of population structure in bivalves (Araneda et al, 2016; Bernatchez et al, 2019; Gormley et al, 2015; Lehnert et al, 2019; Xuereb et al, 2018)

Summary

| INTRODUCTION

The assumption that genetic homogeneity predominates in marine organisms due to the lack of physical barriers and high dispersal potential at all life stages has been challenged in recent years (Allendorf, 2017). A seascape genomics approach using single nucleotide polymorphisms (SNPs) was employed, for the first time, to resolve patterns of population structure of the common cockle between estuaries within a commercially active area (the Irish and Celtic seas), with the goal of identifying management units. For this purpose, we first tested for neutral population structure and assessed the role of current-mediated larval dispersal in shaping it. Larval transport between sites was estimated and connectivity matrices derived from oceanographic modelling, accounting for interannual variability due to biophysical parameters, like spawning time and larval duration

| MATERIALS AND METHODS

Findings

| DISCUSSION