Ecological genetics in the North Atlantic: environmental gradients and adaptation at specific loci

The North Atlantic intertidal community provides a rich set of organismal and environmental material for the study of ecological genetics. Clearly defined environmental gradients exist at multiple spatial scales: there are broad latitudinal trends in temperature, meso-scale changes in salinity along estuaries, and smaller scale gradients in desiccation and temperature spanning the intertidal range. The geology and geography of the American and European coasts provide natural replication of these gradients, allowing for population genetic analyses of parallel adaptation to environmental stress and heterogeneity. Statistical methods have been developed that provide genomic neutrality tests of population differentiation and aid in the process of candidate gene identification. In this paper, we review studies of marine organisms that illustrate associations between an environmental gradient and specific genetic markers. Such highly differentiated markers become candidate genes for adaptation to the environmental factors in question, but the functional significance of genetic variants must be comprehensively evaluated. We present a set of predictions about locus-specific selection across latitudinal, estuarine, and intertidal gradients that are likely to exist in the North Atlantic. We further present new data and analyses that support and contradict these simple selection models. Some taxa show pronounced clinal variation at certain loci against a background of mild clinal variation at many loci. These cases illustrate the procedures necessary for distinguishing selection driven by internal genomic vs. external environmental factors. We suggest that the North Atlantic intertidal community provides a model system for identifying genes that matter in ecology due to the clarity of the environmental stresses and an extensive experimental literature on ecological function. While these organisms are typically poor genetic and genomic models, advances in comparative genomics have provided access to molecular tools that can now be applied to taxa with well-defined ecologies. As many of the organisms we discuss have tight physiological limits driven by climatic factors, this synthesis of molecular population genetics with marine ecology could provide a sensitive means of assessing evolutionary responses to climate change

QUANTITATIVE GENETICS OF JUVENILE GROWTH AND SHAPE IN THE MUD CRAB EURYPANOPEUS DEPRESSUS

Volume: 173Start Page: 461End Page: 47

Semibalanus balanoides recruitment surveys in southwest England, Wales, and Scotland from 2015-2016 (EUROWINTER2 project)

Dataset: UK_Semibalanus_recruitmentThis dataset contains recruitment survey results of Semibalanus balanoides and Chthamalus sp. in southwestern UK, 2015-2016. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/683132NSF Division of Ocean Sciences (NSF OCE) OCE-1129401, National Aeronautics & Space Administration (NASA) NNX11AP77

TEMPORAL VARIATION IN THE REPRODUCTIVE CYCLE OF MYTILUS EDULIS L. (BIVALVIA, MYTILIDAE) FROM LOCALITIES ON THE EAST COAST OF THE UNITED STATES

Volume: 162Start Page: 299End Page: 31

Origin of the antitropical distribution pattern in marine mussels (Mytilus spp.) : routes and timing of transequatorial migration

Many marine species, including mussels in the Mytilus edulis species group (i.e. M. edulis L., M. gal- loprovincialis Lamarck, and M. trossulus Gould), have an antitropical distribution pattern, with closely related taxa occurring in high latitudes of the northern and southern hemispheres but being absent from the tropics. We tested four hypotheses to explain the timing and route of transequatorial migration by species with anti-tropical distributions. These hypotheses yield different predictions for the phylogenetic relationship of southern hemisphere taxa relative to their northern counter-parts. The three Mytilus species were used to test these hy- potheses since they exhibit a typical antitropical distribution and representative taxa occur in both the Pacific and Atlantic. Two types of mtDNA lineages were found among populations of mussels collected from the southern hemisphere between 1988 and 1996; over 90% of the mtDNA lineages formed a distinct subclade which, on average, had 1.4% divergence from haplo-types found exclusively in northern Atlantic populations of M. galloprovincialis. These data indicate that southern hemisphere mussels arose from a migration event from the northern hemisphere during the Pleistocene via an Atlantic route. The remainder of the southern hemisphere lineages

Geographic variation in allele frequency of the gamete recognition protein M7 lysin throughout a mosaic blue mussel hybrid zone

Divergence at gamete recognition loci is hypothesized to result in speciation in broadcast spawning invertebrates. Many gamete recognition loci evolve quickly and show patterns of positive selection, yet the advantage of divergence is rarely known. M7 lysin is a sperm protein in the Mytilus edulis species complex that shows evidence of adaptive evolution. This locus is polymorphic with two distinct clades within Mytilus galloprovincialis, one of which, the D clade, shows the strongest signal of positive selection. We tested whether the geographic patterns in allele frequency were consistent with the hypothesis that positive selection on D clade alleles (GD) was due to reinforcement. Populations of M. edulis showed little evidence of introgression of GD alleles, but there was no consistent evidence of reproductive character displacement. The lack of consistent patterns expected of reinforcement suggests that another mechanism is likely responsible for the adaptive divergence of M7 lysin. © 2013 Springer-Verlag Berlin Heidelberg

Temporal patterns in allele frequencies of the gamete-recognition locus M7 lysin within a population of Mytilus galloprovincialis in southwestern England

Loci that encode proteins involved in gamete recognition often show patterns of rapid adaptive evolution and recent studies have shown that different alleles at gamete-recognition loci can be favoured under different sperm concentrations, leading to density-dependent selection during fertilization. While these density-dependent fertilization processes are likely to vary across time and space, it is possible that they are not typically observed at the larger scale of larval recruitment since most larval cohorts likely consist of multiple pools of larvae produced under a variety of sperm concentrations, which tends to homogenize the allele frequencies across time and space. We tested the hypothesis that allele frequency of the gamete-recognition locus M7 lysin in Mytilus galloprovincialis would show significant temporal variation among cohorts of spat and adult age classes. Adult and juvenile mussels and multiple cohorts of newly settled spat were collected from four locations within a predominantly pure population of M. galloprovincialis in southwestern England. Each mussel was then genotyped at the species-specific locus Glu-5′ and the gamete-recognition locus M7 lysin. Allele frequencies at Glu-5′ did not differ among any age classes or cohorts, suggesting that the samples did not contain migrants from adjacent hybrid populations with M. edulis. Similarly, there was little evidence of variation in allele frequencies at M7 lysin among cohorts of spat or among juvenile and adult age classes. The lack of significant temporal variation in allele frequency at M7 lysin suggests that the results of local and small-scale density-dependent selection may not typically be observed during recruitment of marine organisms with pelagic larval stages