The population structure of the infaunal marine bivalve Ervilia castanea (Montagu, 1803) in the NE Atlantic: investigating species-specific microsatellite patterns

Volcanic oceanic islands are some of the most ecologically and geologically dynamic habitats on Earth. The continuous volcanic and erosional processes to which they are confined to determines the formation of habitats that are highly transformative in their ontogeny and, as a consequence, select for rather unique biological assemblages. Sandy habitats of oceanic islands can repetitively disappear and be regenerated consequently to seasonal oceanographic variations and climatic eustatic variations in the sea-level. For the infaunal invertebrates inhabiting such habitats, these events translate into populations being cyclically extirpated or even, in the case of endemic species, to become extinct. The specificity of the outcome often depends on the specific life-history modes of the species, determining their dispersal and colonization potential and, ultimately, their survival ability. We hereby test the population structure of the marine infaunal bivalve Ervilia castanea (Montagu, 1803). This species is abundantly present in the sandy habitats of the Azores and Madeira Archipelagos in the Northeast Atlantic. By comparing populations in such archipelagos with populations from mainland Europe we aim to understand how specific ecological and geological settings determine the genetic structure of the species. The population genetic structure retrieved from both nuclear microsatellites and the mitochondrial cytochrome oxidase I region show that populations in oceanic islands do not segregate into clusters distinct from mainland populations. Moreover, populations from the Azores and Madeira were not in Hardy-Weinberg Equilibrium and the high percentage of null alleles in the microsatellite regions potentially suggests oceanic islands population to be on a constant selective pressure. Although our dataset does not allow for further genomic investigations, we hereby demonstrate the uniqueness of insular environmental settings, and inquire further investigations into the evolutionary and biogeographic patterns of marine shallow-water infaunal species from oceanic islands.