Next‐generation phylogeography of the cockle Cerastoderma glaucum: Highly heterogeneous genetic differentiation in a lagoon species

Abstract

Aim Coastal lagoons form an intriguing example of fragmented marine habitats. Restricted gene flow among isolated populations of lagoon species may promote their genetic divergence and may thus provide a first step toward speciation. In the present study, the population genetic structure of the lagoon cockle Cerastoderma glaucum has been investigated to clarify the complex phylogeographic pattern found in previous studies, to localize major genetic breaks, and to discuss their origin and maintenance. Location The Atlantic and Mediterranean coasts, including the Baltic, North Sea, and Black Sea. Methods A total of 204 C. glaucum individuals from 14 populations were genotyped using restriction site‐associated DNA sequencing (RADseq). The genetic diversity, divergence, and structure were analyzed using genome‐wide single nucleotide polymorphisms (SNPs). Phylogenetic relationships were inferred under a coalescent model using svdquartets . Results The RADseq approach allowed inferring phylogeographic relationships with an unprecedented resolution. Three deeply divergent lineages were identified within C. glaucum that are separated by many genetic barriers: one lineage in the Aegean–Black Sea region, one in the Ionian Sea, and the last one widely distributed from the Western Mediterranean to the Baltic Sea. The nested branching pattern displayed on the species tree largely agrees with the likely scenario of C. glaucum postglacial expansion from the Mediterranean to the Baltic Sea. Main conclusion The genetic differentiations between geographically separated lagoons proved to be strong, highlighting the evolutionary influence of these naturally fragmented habitats. The postglacial expansion created complex patterns of spatial segregation of genetic diversity with allele frequency gradients in many outlier loci, but also discrepancies between the nuclear and mitochondrial genetic markers that probably arose from genetic surfing of mitochondrial variation.

The many faced symbiotic snakelocks anemone (Anemonia viridis, Anthozoa): host and symbiont genetic differentiation among colour morphs

“…The English populations of A. viridis are therefore the result of a post-glacial recolonization. The differences observed between EngCh and the Mediterranean lineages could then be the result of a vicariance process, in line with what was described for the lagoon cockle Cerastoderma glaucum (Sromek et al 2019) or Cymodocea nodosa (Alberto et al 2008). This cleavage was also supported by the distribution of the symbiont assemblages (Tables 2 and S9).…”

Biotic and abiotic factors shaping the genome of cockle (Cerastoderma edule) in the Northeast Atlantic: a baseline for sustainable management of its wild resources

“…southeast Ireland and Wales) using a classical RADseq technique (Etter et al, 2011). Genetic diversity observed for C. edule in our study was similar to that reported for the sister species C. glaucum (He: 0.078 -0.137; Sromek et al, 2019); however, both cockle species showed lower genetic diversity at genomic scale than other bivalves such as Placopecten magellanicus (He = 0.271 ± 0.133, Van Wyngaarden et al, 2017), Crassostrea virginica (He ~ 0.300; Bernatchez et al, 2019), Ostrea edulis (He ~ 0.300; Vera et al, 2019) and Crassostrea gigas (He ~ 0.300; Gutierrez et al, 2017), suggesting the lower genetic diversity to be a particular feature of the genus Cerastoderma, although we cannot discard that the different methodologies applied for SNP genotyping in those studies might explain this observation.…”

Assessment of genetic diversity in Amomum tsao-ko Crevost & Lemarié, an important medicine food homologous crop from Southwest China using SRAP and ISSR markers

“…A. tsao-ko gradually spread from the origin regions to the periphery through introduction. Generally, a higher genetic similarity is expected between neighboring populations than between distant ones for species with low dispersal ability (Sromek et al 2019 ; Wright 1943 ).…”