Comparative phylogeography of meroplanktonic species, Aurelia spp. and Rhizostoma pulmo (Cnidaria: Scyphozoa) in European Seas

Abstract

Mass occurrences of scypozoan medusae have become increasingly common in recent decades in European seas, including species in the genera Aurelia and Rhizostoma. We inferred the phylogeographic patterns of metagenetic scyphozoa Aurelia spp. and Rhizostoma pulmo from mitochondrial COI and nuclear ITS regions. No genetic structure was detected in R. pulmo over the Mediterranean Sea. By contrast, the phylogeographic analyses confirmed the separation of Aurelia spp. to several proposed cryptic species. Our results do not support the null hypothesis that both genera have concordant phylogeographic patterns. The resolvable parsimony network of haplotypes was retrieved for Aurelia aurita, Aurelia sp. 5, and Aurelia sp. 8 without connectivity between them and no genetic structure were found within those groups. Even though evidence of hybridization was found between A. aurita and Aurelia sp. 5, that did not break down the phylogenetic separation among them. The lowest haplotype and nucleotide diversity were found in samples of Aurelia sp. 8 and R. pulmo from the northern Adriatic, which acts as a sink area due to strong genetic drift. These new findings will facilitate linking the phenotype of the organism and its ability to survive in a particular environment—which shapes phylogeographic patterns.