Genetic diversity and demographic history of the endemic Southeastern Pacific sea urchin Arbacia spatuligera (Valenciennes 1846)

The pattern of the genetic structuring of marine species result from the relationship between homogenizing and structuring factors, together with historical and contemporary processes. Dispersal potential has been described as a homogenizing factor, corroborated by the connectivity paradigm, which states that high dispersers show low or no genetic differentiation. In contrast, biogeographic breaks and oceanic currents have an important role in limiting or enhancing connectivity, being structuring factors. We studied this relationship in Arbacia spatuligera, a subtidal echinoid with a planktonic larval stage, which is distributed along the Southeastern Pacific (SEP). The SEP is divided into two biogeographic provinces with an Intermediate Area between both them, which is delimited by two biogeographic breaks (~30° S and 40°-42° S). Moreover, much of the SEP coast, from ~42° S to 6° S, it is influenced by a complex system of marine currents known as the Humboldt Current System (HCS). Using molecular tools (mtDNA COI) we assessed the genetic diversity and structure of A. spatuligera and inferred its demographic history. Analyses showed that along ca. 3.200 km A. spatuligera has no genetic structure signals, has an unexpected low genetic diversity and a signal of recent demographic expansion dated ~33000 47000 years ago, probably related to the Marine Isotope Stage 3 (MIS3) climatic events. Our results support the hypothesis that dispersal potential is a determining factor of the phylogeographic patterns in the SEP, probably influenced by HCS. We propose that A. spatuligera is a high disperser.