Data from: Genome-wide evidence of environmentally mediated secondary contact of European green crab (Carcinus maenas) lineages in eastern North America

Genetic-environment associations are increasingly revealed through
population genomic data and can occur through a number of processes,
including secondary contact, divergent natural selection, or
isolation-by-distance. Here we investigate the influence of the
environment, including seasonal temperature and salinity, on the
population structure of the invasive European green crab (Carcinus maenas)
in eastern North America. Green crab populations in eastern North America
are associated with two independent invasions, previously shown to consist
of distinct northern and southern ecotypes, with a contact zone in
southern Nova Scotia, Canada. Using a RAD-seq panel of 9137 genome-wide
SNPs, we detected 41 SNPs (0.49%) whose allele frequencies were highly
correlated with environmental data. A principal components analysis of 25
environmental variables differentiated populations into northern,
southern, and admixed sites in concordance with the observed genomic
spatial structure. Furthermore, a spatial principal components analysis
conducted on genomic and geographic data revealed a high degree of global
structure (p<0.0001) partitioning a northern and southern ecotype.
Redundancy and partial redundancy analyses revealed that among the
environmental variables tested, winter sea surface temperature had the
strongest association with spatial structuring, suggesting that it is an
important factor defining range and expansion limits of each ecotype.
Understanding environmental thresholds associated with intraspecific
diversity will facilitate the ability to manage current and predict future
distributions of this aquatic invasive species.

遗传-环境关联（Genetic-environment associations）正通过群体基因组数据（population genomic data）被日益揭示，其形成可经由多种过程，包括二次接触（secondary contact）、分歧性自然选择（divergent natural selection）或距离隔离（isolation-by-distance）。本研究旨在探究环境因素（包括季节性温度与盐度）对北美东部入侵性欧洲绿蟹（*Carcinus maenas*）种群结构的影响。北美东部的绿蟹种群与两次独立入侵事件相关，此前研究表明其包含不同的北方和南方生态型（ecotypes），接触带位于加拿大新斯科舍省南部。利用包含9137个全基因组单核苷酸多态性（SNPs）的RAD-seq面板，我们检测到41个SNPs（0.49%），其等位基因频率与环境数据高度相关。对25个环境变量的主成分分析（principal components analysis）将种群划分为北方、南方和混合位点，与观察到的基因组空间结构一致。此外，基于基因组和地理数据的空间主成分分析（spatial principal components analysis）揭示了高度显著的全局结构（p<0.0001），该结构划分出北方和南方生态型。冗余分析（redundancy analysis）与偏冗余分析（partial redundancy analysis）显示，在测试的环境变量中，冬季海表温度与空间结构的关联最强，表明其是定义各生态型分布范围和扩张极限的重要因素。理解与种内多样性（intraspecific diversity）相关的环境阈值（environmental thresholds），将有助于管理该水生入侵物种的当前分布并预测其未来分布。