Dispersal and speciation: The cross Atlantic relationship of two parasitic cnidarians

摘要

How dispersal strategies impact the distribution of species and subsequent speciation events is a fundamental question in evolutionary biology. Sedentary benthic marine organisms, such as corals or sea anemones usually rely on motile larval stages for dispersal and therefore have a relatively restricted distribution along coasts.Edwardsiella lineataandEdwardsiella carneaare virtually indistinguishable edwardsiid sea anemones native to the east American and the Northern European coast, respectively.E. lineatais a facultative parasite to the ctenophoreMnemiopsis leidyi, while the life cycle ofE. carneais unknown. RecentlyM. leidyiwas found in the Skagerrak carryingEdwardsiellasp. parasites, which raised the intriguing possibility that the invasive comb jellies acted as cargo for the facultativeE. lineataparasites to establish a new population in Northern Europe. Here, we assessed the genetic differences between these two crypticEdwardsiellaspecies and isolated parasites from the invasive comb jellyM. leidyiin Sweden by comparing rRNA, whole transcriptomes, SNPs, ITS2 sequences and the gene complements of key developmental regulators, the Wnt gene family. We show thatE. carneaand the parasite transcriptomes are more than 99% identical, hence demonstrating thatE. carneahas a previously unknown parasitic life stage. ITS2 sequence analysis ofE. carneaandE. lineatasuggest that they may not be reproductively isolated. The transcriptomes ofE. lineataandE. carneaare ～97% identical. We also estimate that the species diverged between 18.7 and 21.6 million years ago.