Population genetic structure in the coral reef associated ascidian, Polycarpa aurata, throughout Wallacea, Indonesia

Abstract We investigated the population genetic structure of the coral reef associated ascidian, Polycarpa aurata throughout the marine region of Wallacea, Indonesia. Four hundred individuals from 12 sampling locations were genotyped at 14 microsatellite loci. We detected strong evidence for population structuring. F S T ′ and F S T values are high and significant indicating restricted gene flow between populations. Bayesian clustering techniques provided further evidence in support of population genetic divergence, and we did not detect a significant pattern of isolation by distance. We suggest that the extremely heterogeneous environment throughout Wallacea coupled with the short pelagic larval duration is responsible for creating the patterns we report. Differences in habitat type create numerous opportunities for selection to act, the synergistic effects of local adaption, selection and limited larval dispersal promote an increase in the frequency of traits that enhance survival in the immediate environment, meaning that recruits from the local area are favoured over those not from the immediate vicinity. This leads to reproductive isolation, adaptive divergence and finally parapatric speciation. Work such as this allows us to further understand the evolutionary processes that have contributed to creating the most biodiverse marine region on the planet. By demonstrating the existence of population genetic structure and divergence over short distances, we provide support for the centre of origin hypothesis.