Phylogeography of the barren forming sea urchin Diadema africanum (Rodríguez et al. 2013).
Supervisors: José C Hernández. Rocío Pérez-Portela (U La Laguna)
Phylogeography is a field defined as the study of genetic data in a geographic context, analyzing geographical distribution of genealogical lineages, often performed between populations of the same species. In this study, populations of the sea urchin Diadema africanum, from two contrasting regions have been investigated (Canary Islands and Cape Verde). The connectivity of these two archipelagos has been discussed in recent studies. Despite of its relatively close geographical proximity, the biodiversity observed between both regions are distinct enough to consider Cape Verde as a different biogeographical unit. Thus, studying the genetic connection between populations from both regions seems to be of great interest. D. africanum is a key herbivore in the subtropical and tropical rocky reefs of the East Atlantic Archipelagos. This species is an organism commonly found at shallow waters but that can reach depths down to 70 metres. Our interest in D. africanum is due to its voracious grazing activity on shallow rocky reefs which led to the extreme depletion of the macroalgae stands, forming extensive barren grounds. This key role in coastal habitats and its life history make D. africanum an interesting species to study. This research has used 249 new DNA sequences from the mitochondrial gene cytochrome c-oxidase subunit 1 (COI) to study the phylogeography of D. africanum from 14 localities along Cape Verde and Canary Islands archipelagos. Different parameters such as genetic diversity, phylogeographic and demographic features were analyzed. The results showed low genetic diversity with 33 haplotypes grouped in one main haplogroup. It was also depicted that population from the two studied regions did not show any genetic differences. A rather high homogeneity was found between all those populations that could be explained by the high larval dispersal capacity of this species. The star-shaped topology of the haplotype network and the unimodal mismatch distribution of the studied samples did suggest a very recent demographic expansion still occurring. During one of the glacial cycles of the Pleistocene, Late Pliocene, speciation of D. africanum occurred and produced an intense founder effect. This potential founder effect, which happened during the speciation process and the posterior demographic expansion that seems to continue today, are likely the causes of the low genetic diversity and absence of differentiation observed in D. africanum. Under a scenario of demographic expansion and large dispersal potential, their populations are very homogeneous across the studied archipelagos.