Sea surface currents and geographic isolation shape the genetic population structure of a coral reef fish in the Indian Ocean

Abstract

In this contribution, we determine the genetic population structure in the Skunk Clownfish (Amphiprion akallopsisos) across the Indian Ocean, and on a smaller geographic scale in the Western Indian Ocean (WIO). Highly restricted gene flow was discovered between populations on either side of the Indian Ocean using the control region as a mitochondrial marker (mtDNA). We verify this conclusion using 13 microsatellite markers and infer fine scale genetic structuring within the WIO. In total 387 samples from 21 sites were analysed using mtDNA and 13 microsatellite loci. Analysis included estimation of genetic diversity and population differentiation. A haplotype network was inferred using mtDNA. Nuclear markers were used in Bayesian clustering and a principal component analysis. Both markers confirmed strong genetic differentiation between WIO and Eastern Indian Ocean (EIO) populations, and a shallower population structure among Malagasy and East African mainland populations. Limited gene flow across the Mozambique Channel may be explained by its complex oceanography, which could cause local retention of larvae, limiting dispersal between Madagascar and the East African coast. Two other potential current-mediated barriers to larval dispersal suggested in the WIO, the split of the SEC at approximately 10° S and the convergence of the Somali Current with the East African Coast Current at approximately 3° S, were not found to form a barrier to gene flow in this species.

Cryptic diversity and limited connectivity in octopuses: Recommendations for fisheries management

“…This is congruent with the results of Tajima’s D-test, Fu’s Fs test, the mismatch distribution analysis and Rogers’ test for sudden population expansion, that suggest demographic growth. This finding is similar to the population expansion reported in the WIO for the African giant mud crab Scylla serrata [66], the skunk clownfish Amphiprion akallopisos [68] and the mangrove whelk Terebralia palustris [30].…”

“…The splitting of the SEC into the southward Southeast Madagascar Current (SEMC) and the northward Northeast Madagascar Current (NEMC) at the East coast of Madagascar might be a reason for restricted gene flow between sites in Northeast Madagascar and southern sites. A similar pattern was found for the skunk clownfish, Amphiprion akallopisos , for which the population from Sm was significantly differentiated from the other WIO populations [68]. The southernmost location in Madagascar (Fd) is very likely under the influence of the SEMC, what might prevent exchange and gene flow with sample sites at the West coast of Madagascar or African mainland.…”

“…Due to low sample size in the South African localities and the limited number of sites investigated, further sampling and research needs to be conducted in order to confirm either of both hypothesis. Anyhow, the uniqueness of populations from the WIO compared with populations elsewhere in the Indian Ocean was also found for other species such as the skunk clownfish [68] and the mud crab Scylla serrata [77].…”

“…To be sure that the observed genetic structure patterns that were found with COI are not influenced by these shortcomings, nuclear loci should be analysed additionally in the future [87]. By comparing the results of mtDNA and nuclear markers such as microsatellites, the suitability of mtDNA can be validated and additional information might be obtained [66, 68].…”

Estimating Connectivity Through Larval Dispersal in the Western Indian Ocean

“…Both genetic and hydrodynamic modeling studies have been used to infer levels of connectivity and gene flow among populations in the WIO. Genetic studies have focused reef fish (e.g., Dorenbosch et al, ; Huyghe & Kochzius, , ; Muths et al, ; Otwoma & Kochzius, and Visram et al, ) and coral species (e.g., Macdonald et al, ; Van der Ven et al, ). While modeling using Lagrangian models has been extensively used on global to regional scales (e.g., Cowen et al, ; Cowen & Sponaugle, ; Kool et al, ; Paris et al, ; Treml et al, ; Wood et al, , ), their use in the WIO has been limited.…”