Morphological and molecular assessment of large sea anemones (Actiniaria: Actiniidae) in Newfoundland (eastern Canada)

There and Back Again: The Unexpected Journeys of Metridium de Blainville, 1824 between the Old Oceans and throughout the Modern World

AbstractMembers of the sea anemone genus Metridium are abundant in temperate rocky habitats and fouling communities. Their biogeographic history is expected to reflect changes in currents and habitats that have influenced benthic communities, such as the climate-influenced changes that occurred during the Last Glacial Maximum. More recently, however, anthropogenic influences such as shipping transportation and the creation of artificial habitat have altered and affected the composition of modern-day marine communities. Here we use sequence-capture data to examine the genetic structure of Metridium across its shallow-water distribution to (1) evaluate species boundaries within Metridium, (2) elucidate the dispersal history of Metridium between and among oceans, and (3) assess the influence of anthropogenic movement on modern-day populations. We find strong evidence for two species within Metridium: M. farcimen and M. senile. Dispersal from the Pacific to the Atlantic included a subsequent isolation of a small population in or above the Bering Sea, which has presumably moved southward. Within the native range of M. senile, admixture is prevalent even between oceans as a result of anthropogenic activities. The nonnative populations in Chile and the Falkland Islands came from at least two distinct introduction events originating from both coasts of the United States in the North Pacific and North Atlantic Oceans. Hybridization between M. senile and M. farcimen is documented as occurring in anthropogenically influenced habitats. The heavy influence from anthropogenic activities will continue to impact our understanding of marine organisms, particularly within the native range and for those that are easily transported across long distances.

Comparison of sequence-capture and ddRAD approaches in resolving species and populations in hexacorallian anthozoans

Genome-level sequencing is the next step in understanding species-level relationships within Anthozoa (soft corals, anemones, stony corals, and their kin) as morphological and PCR-directed (single-locus) sequencing methods often fall short of differentiating species. The sea anemone genus Metridium is a common northern temperate sea anemone whose species are difficult to differentiate using morphology alone. Here we use Metridium as a case study to confirm the low level of information available in six loci for species differentiation commonly sequenced for Actiniaria and explore and compare the efficacy of ddRAD and sequence-capture methods in species-level systematics and biogeographic studies. We produce phylogenetic trees from concatenated datasets and perform DAPC and STRUCTURE analyses using SNP data. The six conventional loci are not able to consistently differentiate species within Metridium. The sequence-capture dataset resulted in high support and resolution for both current species and relationships between geographic areas. The ddRAD datasets displayed ambiguity among species, and support between major geographic groupings was not as high as the sequence-capture datasets. The level of resolution and support resulting from the sequence-capture data, combined with the ability to add additional individuals and expand beyond the genus Metridium over time, emphasizes the utility of sequence-capture methods for both systematics and future biogeographic studies within anthozoans. We discuss the strengths and weaknesses of the genomic approaches in light of our findings and suggest potential implications for the biogeography of Metridium based on our sampling.