Spatio-temporal analysis of genetic diversity in the sibling species Contracaecum osculatum sp. B: a tool for monitoring trophic-web dynamics in Arctic Sea waters

Global changes in the marine Arctic ecosystem affecting the demography of fish and seal populations may also alter their anisakid parasite populations size, potentially leading to genetic erosion in gene pools. Contracaecum osculatum sp. B, an Arctic member of the C. osculatum (s.l.) species complex, parasitizes Arctic and sub-Arctic seals and fish. This study aimed to compare parasite genetic diversity across the Nordic Seas over time, using historical specimens (1985-1986) and contemporary ones (2021-2022) obtained from seals and fish of the same regions. Parasites were first identified by sequence analysis of mtDNA cox2 and ITS rDNA, then genotyped at seven SSRs nuclear DNA loci, developed in the present study. The population genetic structure of C. osculatum sp. B revealed the existence of two parasite subpopulations, a pattern that appears to be mostly influenced by the population structure of the seal hosts in the area. High genetic polymorphism was observed in the parasite species, at both nuclear and mitochondrial level. In the contemporary parasite population gene pool, some rare haplotypes in mtDNA cox2 and rare alleles at SSRs-DNA loci appeared to be lost in comparison to the historical population; while, novel unique alleles and haplotypes simultaneously emerged. Overall, these findings would suggest the occurrence of an initial decline in parasite population size, followed by a period of demographic stability, and a population increase in recent years. Similar demographic patterns have been documented in the host populations over the same time scale. Genetic polymorphisms in anisakids across temporal scales may help unravel and monitor trophic-web dynamics in the Arctic marine ecosystem under global change.