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Data from: Genomic evidence of hybridization between two independent invasions of European green crab (Carcinus maenas) in the Northwest Atlantic
Jeffery, Nicholas W.; DiBacco, Claudio; Wringe, Brendan F.; Stanley, Ryan R.E.; Hamilton, Lorraine C.; Ravindran, Praveen N.; Bradbury, Ian R. — 2017-03-22 Invasive species have been associated with significant negative impacts in their introduced range often outcompeting native species, yet the long-term evolutionary dynamics of biological invasions are not well understood. Hybridization, either among waves of invasion or between native and introduced populations, could alter the ecological and evolutionary impacts of invasions yet has rarely been studied in marine invasive species. The European green crab (Carcinus maenas) invaded eastern North America twice from northern and southern locations in its native range. Here we examine the frequency of hybridization among these two distinct invasions at locations from New Jersey, USA to Newfoundland, Canada using restriction-site associated DNA sequencing (RAD-seq), microsatellite loci, and COI mtDNA sequences. We used Bayesian clustering and hybrid assignment analyses to investigate hybridization between the northern and southern populations. Of the samples analyzed, six locations contained at least one hybrid individual, while two locations were characterized by extensive hybridization, with 95% of individuals collected from Placentia Bay, Newfoundland being hybrids (mostly F2), and 90% of individuals from Kejimkujik, Nova Scotia being classified as hybrids, mostly backcrosses to the northern ecotype. The presence of both F2 hybrids and backcrossed individuals suggests that these hybrids are viable and introgression is occurring between invasions. Our results provide insight into the demographic and evolutionary consequences of hybridization between independent invasions, and will inform the management of green crabs in eastern North America.
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Data from: Temporal dynamics of the genetic clines of invasive European green crab (Carcinus maenas) in eastern North America
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Lehnert, Sarah J.; DiBacco, Claudio; Jeffery, Nicholas W.; Blakeslee, April M.H.; Isaksson, Jonatan; Roman, Joe; Wringe, Brendan F.; Stanley, Ryan R.E.; Matheson, Kyle; McKenzie, Cynthia H.; Hamilton, Lorraine C.; Bradbury, Ian R.; Stanley, Ryan R. E.; Blakeslee, April M. H. — 2018-06-05 Two genetically distinct lineages of European green crabs (Carcinus maenas) were independently introduced to eastern North America, the first in the early 19th century and the second in the late 20th century. These lineages first came into secondary contact in southeastern Nova Scotia, Canada (NS), where they hybridized, producing latitudinal genetic clines. Previous studies have documented a persistent southward shift in the clines of different marker types, consistent with existing dispersal and recruitment pathways. We evaluated current clinal structure by quantifying the distribution of lineages and fine-scale hybridization patterns across the eastern North American range (25 locations, ~39-49°N) using informative single nucleotide polymorphisms (SNPs; n=96). In addition, temporal changes in the genetic clines were evaluated using mitochondrial DNA and microsatellite loci (n=9-11) over a 15-year period (2000-2015). Clinal structure was consistent with prior work demonstrating the existence of both northern and southern lineages with a hybrid zone occurring between southern New Brunswick (NB) and southern NS. Extensive later generation hybrids were detected in this region and in southeastern Newfoundland. Temporal genetic analysis confirmed the southward progression of clines over time; however, the rate of this progression was slower than predicted by forecasting models, and current clines for all marker types deviated significantly from these predictions. Our results suggest that neutral and selective processes contribute to cline dynamics, and ultimately, highlight how selection, hybridization, and dispersal can collectively influence invasion success.
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Data from: Genome-wide evidence of environmentally mediated secondary contact of European green crab (Carcinus maenas) lineages in eastern North America
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Jeffery, Nicholas W.; Bradbury, Ian R.; Stanley, Ryan R.E.; Wringe, Brendan F.; Van Wyngaarden, Mallory; Lowen, J. Ben; McKenzie, Cynthia H.; Matheson, Kyle; Sargent, Philip S.; DiBacco, Claudio; Stanley, Ryan R. E. — 2018-01-19 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.

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(Author: Stanley, Ryan R.E.)

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