Remarkable population structure in the tropical Atlantic lace corals Stylaster roseus (Pallas, 1766) and Stylaster blatteus (Boschma, 1961)

Abstract

Biodiversity on coral reefs depends not only on primary reef-builders, but also on associated taxa that create microhabitats for other species. Hydrocorals of the genus Stylaster, commonly known as lace corals, form small branching colonies that enhance three-dimensional complexity on reefs and are known to support a variety of commensal species. Furthermore, the genus is highly speciose, further increasing biodiversity. Despite their important ecological roles, little is known about the evolutionary history and the intraspecific diversity and structure in these broadly distributed hydrocorals. Here, we assessed the phylogenetic relationships among Atlantic species in the genus Stylaster and examined the genetic structure of S. roseus in the Tropical Western Atlantic (Caribbean and Brazil) and of S. blatteus in the Tropical Eastern Atlantic (Africa), using DNA sequences from the 16S ribosomal gene. Time-calibrated phylogenetic analyses showed that S. roseus and S. blatteus diverged at ~ 24.6 Ma. A well-supported Brazilian clade within S. roseus indicates a possible cryptic species that diverged at ~ 11.6 Ma, consistent with the formation of the Amazon River at 9 Ma (Hoorn et al. in Glob Planet Change 153:51–65, 2017). Strong genetic structure was observed even over moderate distances, with ΦST values over all populations being 0.98 for S. roseus and 0.90 for S. blatteus. Nearly, all haplotypes were private (found in a single location) and diverged by many mutational steps from one another. In contrast, genetic diversity was low at the local scale for both species, with most sites showing no variation (a single haplotype). These results are coherent with the reproductive strategy of Stylasteridae, where larvae are brooded and are highly developed at the time of release, often settling near the parental colony. Limited dispersal coupled with possible clonal reproduction have likely contributed to the high levels of genetic differentiation observed here. Lace corals show unusual reproductive and population dynamics compared to other reef inhabiting cnidarians. Future work may reveal additional cryptic diversity in this poorly studied family.

Millepora spp. as Substrates of Their Hydrozoan Counterparts Stylaster sp. in the Pacific Ocean

“…Based on this information and our data being limited to photographs, we cannot establish the identity of the Millepora species we observed associating with Stylaster species with certainty. Although we could not identify Millepora to species level, it is clear that the set of species involved here are different than in the previously reported relationship, as both M. alcicornis and S. roseus are Caribbean species [16,17]. Species with similar habits of symbiosis with Millepora have been found to exhibit profound genetic differentiation across different regions.…”