Phylogenetic Relatedness within the Internally Brooding Sea Anemones from the Arctic-Boreal Region

Simple Summary Sea anemones owe their phylogenetic uncertainty to the lack of correspondence between taxonomy and morphological and biological traits. We focused on the phylogenetic relationships within the genera Urticina, Cribrinopsis, and Aulactinia including brooding Arctic-boreal species that are found in aggregations in intertidal and subtidal zones. Nuclear 28S ribosomal DNA partial sequences were desirable for analyses of taxonomic relationships between these genera. Mitochondrial and morphological genealogies did not appear to be representative and sufficient for separating taxa lower than the level of families. Despite brooding strategy has been described as increasing offspring survival but decreasing dispersal potential, the dispersion of the juveniles of the studied Arctic-boreal species might be sufficient to settle remote habitats. Phylogenetic analyses based on mitochondrial 16S rDNA, nuclear 28S rDNA, and morphological and ecological traits of Aulactinia, Urticina and Cribrinopsis sea anemones inhabiting the Arctic-boreal region indicate discordances between trees derived from molecular sequences and those based on morphological traits. Nuclear genes were more informative than mitochondrial and morphological datasets. Our findings indicate that 16S rDNA has limited applicability for phylogenetic analyses at lower taxonomic levels and can only be used for distinction of families. Although 28S rDNA allowed for the classification of distinct genera, it could not confirm that species of Urticina and Cribrinopsis, which appeared to be closely related, were correctly separated into two different genera. The nuclear tree revealed inconsistencies between specimens belonging to European Urticina crassicornis and Pacific U. crassicornis; the latter seems to be a different species. In contrast to Pacific U. crassicornis, the specimens collected from different localities in the Barents Sea are on the same tree branch. The same was observed for specimens of Aulactinia stella. Both species brood their young internally. The dispersal of sea anemones with brooding juveniles seems to be less limited than expected and might be sufficient to settle habitats more than a thousand kilometers away.