Cryptic species diversity and reproductive isolation among sympatric lineages ofStrongylocentrotussea urchins in the northwest Atlantic

Abstract

Distinguishing between intra-and inter-specific variation in genetic studies is critical to understanding evolution because the mechanisms driving change among populations are expected to be different than those that shape reproductive isolation among lineages. Genetic studies of north Atlantic green sea urchins Strongylocentrotus droebachiensis (Müller, 1776) have detected significant population substructure and asymmetric gene flow from Europe to Atlantic Canada and interspecific hybridization between S. droebachiensis and Strongylocentrotus pallidus (Sars, 1871). However, combined with patterns of divergence at mtDNA sequences, morphological divergence at gamete traits suggests that the European and North American lineages of S. droebachiensis may be cryptic species. Here, we use a combination of cytochrome c oxidase subunit I (COI) sequences and single nucleotide polymorphisms (SNPs) to test for cryptic species within Strongylocentrotus sea urchins and hybrids between S. droebachiensis and S. pallidus populations. We detect striking patterns of habitat and reproductive isolation between two S. droebachiensis lineages, with offshore deep-water collections consisting of S. pallidus in addition to a cryptic lineage sharing genetic similarity with previously published sequences from eastern Atlantic S. droebachiensis. We detected only limited hybridization among all three lineages of sea urchins, suggesting that shared genetic differences previously reported may be a result of historical introgression or incomplete lineage sorting.

Cycles of trans‐Arctic dispersal and vicariance, and diversification of the amphi‐boreal marine fauna

“…They have been rarely used in this context, except for the deeper lineages that were initially easily distinguished even by the slowly evolving allozyme markers. Evolution of incompatibility over a single glacial cycle appears unlikely, and for young lineages, observations of haplotype mixing plausibly reflect merging of the refugial ancestries (however, see Addison & Kim, 2018). This was inferred in Hiatella L in a broad sector of the NW Atlantic range (Laakkonen, Strelkov, & Väinölä, 2015).…”

“…Although secondary contacts of young lineages seem to be common in the data, so far there is little conclusive evidence of such repeated process over a broader time frame. A broader genomic sampling should elucidate this, and interesting histories to be addressed could involve Gammarus setosus and Balanus crenatus , apart from the ongoing genomics of Strongylocentrotus , which provides insights also to rapid reproductive isolation and habitat segregation in contacts of young lineages ( Addison & Kim, 2018).…”

“…For deeper lineages (often taxa), there are now several examples of introgressive hybridization following a post‐glacial secondary contact. Inter‐taxon gene flow has substantially shaped the genetic diversity and systematic identities of some North Atlantic populations of Limecola, Mytilus , Clupea and Strongylocentrotus (Addison & Kim, 2018; Laakkonen, Strelkov, Lajus, & Väinölä, 2015; Nikula, Strelkov, & Väinölä, 2008; Rawson & Hilbish, 1998; Strelkov et al., 2007; Väinölä & Strelkov, 2011), and the observations on these contact zones were a central incentive for this broader survey. Interestingly, no further conclusive evidence of such contacts emerged however.…”

“…We recorded overlapping distributions of sister species or distinct genetic lineages in nine vertebrate and eleven invertebrate taxa, or overall some 22% of the genera studied (Tables 1 and 3) Addison & Kim, 2018). This was inferred in Hiatella L in a broad sector of the NW Atlantic range .…”

Fine-Scale Population Genetic Structure and Parapatric Cryptic Species of Kuruma Shrimp (Marsupenaeus japonicus), Along the Northwestern Pacific Coast of China

“…In addition, previous laboratory results indicated that the sympatric areas were limited to the Huilai-adjacent sea area (He et al, 2012). It is important to determine the areas of sympatry and understand the ecological differences of sympatric cryptic species, which are valuable systems for exploring gene exchange, introgressive hybridization, and species differentiation (Michel et al, 2010;Addison and Kim, 2018).…”