Phylogenetic and phylogeographic assessment of the temperate octocoral Eunicella verrucosa

Abstract

The three-dimensional structure of gorgonian octocoral, like Eunicella, can provide vital habitat for other marine organisms and are thus considered ecosystem engineers. As they are ecosystem engineers, the conservation of Eunicella can deliver benefit to other marine organisms and thus their conservation can have a significant impact. Phylogenetic assessment of a species is pivotal in order to inform management efforts and conservation strategies accurately. Unfortunately, phylogenetic assessment of octocoral has been massively hindered by a lack of variation in their mitochondrial genomes. This is highly evident in the Eunicella genus, as previous studies have shown no variation in the mitochondrial protein-coding gene cox1. In Chapter 2, novel primers were successfully developed and exploited to explore the phylogenetic relationships between three predominant Atlantic-Mediterranean members of Eunicella (E. verrucosa, E. singularis and E. cavolini). This is one of the first studies to identify variation in the mitochondrial genomes of Eunicella. In Chapter 3, complete mitochondrial genomes of 19 E. verrucosa individuals were sequenced. Only two E. verrucosa genotypes were observed. 17 E. verrucosa individuals showed a widespread genotype and two E. verrucosa individuals, from Lion Rock, Isle of Scilly, southwest England, showed a unique genotype. Even compared to the known low levels of variation in the mitogenomes of octocoral, extremely low levels of variation were observed between the mitogenomes of E. verrucosa and E. cavolini, suggesting a recent divergence of the species. Holaxonia-phylogenies were produced by exploiting partial contigs of mtMutS and complete mitochondrial protein-coding sequences. These phylogenies support the inclusion of Eunicella in the family Gorgonidae, in line with previous research. The confirmation of Eunicella spp. position within the octocoral phylogeny will allow for properly informed conservation efforts. The conservation of Eunicella spp. is especially important, as they are ecosystem engineers it is highly probable the conservation of Eunicella spp. will have secondary impact on other marine organisms that rely on Eunicella spp. for habitat or resources.