Molecular identification of Cnidarians in Maltese waters, Central Mediterranean

Abstract

Cnidarians, inhabiting Maltese waters from coastal to pelagic environments, comprise diverse taxonomic groups. Molecular genetic research, and its applications to improve on existing taxonomic identification practices, have revealed greater genetic diversity in the phylum Cnidaria in the Mediterranean Sea; a region that is under pressure from increasing anthropogenic activities and therefore in urgent need for targeted conservation measures on identifiable biodiversity. This study made use of three genetic loci: two of which were mitochondrial genes, cytochrome oxidase c subunit I (COi) and 168 rRNA (168); and one nuclear gene, 288 rRNA (288). Experiments and data analyses targeted the assessment of their effectiveness in the identification of cnidarian species. The protocols established in this study have amplified and sequenced different species from the classes Anthozoa, Hydrozoa and Scyphozoa. Comparisons of the current data with that available in databases have shown that even though the 168 protocols are usually very efficiently amplified, this was not so for species of the class Anthozoa where the data generated was not good enough to tell all species apan. In fact, most of the anthozoan species analysed here had matches greater than 99.7% to other anthozoan species. However, such low level of interspecific divergence was not noted in the other two classes, thus making 168 good for identifying hydroids and scyphozoans. A similar scenario was noted using COi, where the divergence between the anthozoans analysed in this study and interspecific data available in genetic databases has shown more than one species with a divergence of less than 1.5%. This indicates that this class has a slow rate of mitochondrial evolution. On the other hand, the overlapping between anthozoan species was noted to be less for the 288 gene though the amplification success of this gene was fairly low. The latter presents technical issues related to the application of this gene on a wider scale. A combination of the three genes was found to efficiently discriminate between the species that were analysed. The phylogenetic trees confirmed that each class is monophyletic after using both mitochondrial and nuclear data. Moreover, current data together with that publically available in databases was used to evaluate phylogeographic connections for each species, to better understand their intraspecific diversity. The research results revealed that the choice of the genetic markers determines the success of the species identification for cnidarians. This has direct implications on the effectiveness and efficiency in utilizing these techniques as identification tools for monitoring native or alien biodiversity in support of conservation, in the fast changing Mediterranean marine environment. Some of these species are useful environmental indicators for detecting ecosystem changes, so a better understanding of their occurrence and diversity give us the upper hand in finding mitigation measures to safeguard regional biodiversity.