Highly restricted gene flow between disjunct populations of the skunk clownfish (Amphiprion akallopisos) in the Indian Ocean

摘要

The skunk clownfish (Amphiprion akallopisos) has a disjunct distribution, occurring in the Eastern Indian Ocean (EIO) and the Western Indian Ocean (WIO), separated by several thousands of kilometres. Information on connectivity of marine species is very important for the correct spacing of marine protected areas, a powerful instrument for the protection of coral reefs. The population genetic structure of A.akallopisos was analysed in order to investigate connectivity amongst populations and to explain the disjunct distribution of the species. A fragment of the mitochondrial control region was used to investigate the genetic population structure. Fin clips were collected from 263 individuals at 14 sites in the WIO and three sites in the EIO. The obtained DNA sequences were used to calculate genetic diversity, evaluate demographic history and to construct a haplotype network. An analysis of molecular variance (AMOVA) was conducted to evaluate the significance of the observed genetic population structure. None of the identified 69 haplotypes was shared between the WIO and EIO. Haplotype as well as nucleotide diversity was considerably higher in the EIO than in the WIO. Significant genetic population structure was revealed by an AMOVA with an overall phi(st)-value of 0.28 (P<0.001) in the Indian Ocean. The overall AMOVA (phi(st)=-0.00652) was not significant in the EIO, but was significant in the WIO (phi(st)=0.016; P<0.01). Demographic analysis indicated population expansion in the EIO and WIO. Population genetic analysis revealed highly restricted gene flow between the EIO and WIO. Genetic diversity was much higher in the EIO than in the WIO, suggesting that the EIO is the geographical origin of the species. Given the large distance between the disjunct populations and the short pelagic larval duration, long-distance dispersal is rather unlikely. A stepping stone model involving islands in the Central Indian Ocean is a more likely scenario for colonization of the WIO.