Heterogeneous microgeographic genetic structure of the common cockle (Cerastoderma edule) in the Northeast Atlantic Ocean: biogeographic barriers and environmental factors

A common garden experiment supports a genetic component underlying the increased resilience of common cockle (Cerastoderma edule) to the parasite Marteilia cochillia

“…Positive F IS values have been commonly reported in mollusks (Pino‐Querido et al, 2015) and specifically in common cockle (Vera et al, 2022), and have been mostly attributed to the presence of null alleles related to the high nucleotide polymorphisms reported in this group (Guo et al, 2023; Zhan et al, 2009). However, F IS values in our study were significantly higher than those previously reported in shellfish beds from Galicia (average F IS = 0.104; Vera et al, 2023) and could be either related to the mixing of different cohorts originated from small number of contributors when obtaining progenies at hatchery (Wahlund effect) or to the particular high heterozygote deficit detected at specific loci, such as CE2, CE11, CE25, CE50, CE51, CE52, and CE53 (Figure S4).…”

“…Unlike the genomic screening by Vera et al (2023), we observed a highly significant genetic differentiation with the 45 selected SNPs between Noia and Lombos do Ulla stocks ( F ST = 0.082, p = 0) and the genetic structure analysis without a priori information (STRUCTURE, DAPC) identified two main clusters associated with the naïve and the affected stocks, respectively. Strong selective pressure, such as that caused by M .…”

“…All estimators consistently showed higher genetic S3 and S4; Figure 4). However, in a previous study, cockle samples from the same shellfish beds of Ría de Arousa and Ría de Muros-Noia did not show genetic diversity differences using a 9250 SNP 2b-RADseq panel (Vera et al, 2023).…”

“…All estimators consistently showed higher genetic diversity figures in the samples from the affected stock (Lombos do Ulla) than those from the naïve stock (Noia): Ar (1.838 vs. 1.696), H E (0.321 vs. 0.256), and H O (0.220 vs. 0.173) (Wilcoxon rank paired tests p < 0.001 in all cases) (Tables S3 and S4; Figure 4). However, in a previous study, cockle samples from the same shellfish beds of Ría de Arousa and Ría de Muros‐Noia did not show genetic diversity differences using a 9250 SNP 2b‐RADseq panel (Vera et al, 2023). Since these 45 SNPs were specifically selected for their association with marteiliosis resilience in the affected stock (Pampín et al, 2023), the most likely explanation is that they are located in genomic regions differentiated from the neutral background.…”

“…The common garden design enabled us to validate the association of the selected SNPs with marteiliosis resilience in a new sampling scenario and to ascertain their role both in the long term, by comparing the genetic differentiation between naïve and affected stocks, as well as in the short term, by analyzing the growing‐out stage in the naïve stock in two shellfish beds. It is important to point out that no genetic differentiation was detected between samples from Ría de Muros‐Noia and Ría de Arousa, where shellfish beds of naïve and affected stocks are, respectively, located using a genomic screening with ~9000 SNPs ( F ST not ≠ 0; Vera et al, 2023). This genetic homogenization has been attributed to the high dispersal capacity of cockles during planktonic free‐living stages and to its large population size (Vera et al, 2022).…”