Abstract
Phylogeographic patterns and population structure of the pelagic Indian mackerel, Rastrelliger kanagurta were examined in 23 populations collected from the Indonesian-Malaysian Archipelago (IMA) and the West Indian Ocean (WIO). Despite the vast expanse of the IMA and neighbouring seas, no evidence for geographical structure was evident. An indication that R. kanagurta populations across this region are essentially panmictic. This study also revealed that historical isolation was insufficient for R. kanagurta to attain migration drift equilibrium. Two distinct subpopulations were detected between the WIO and the IMA (and adjacent populations); interpopulation genetic variation was high. A plausible explanation for the genetic differentiation observed between the IMA and WIO regions suggest historical isolation as a result of fluctuations in sea levels during the late Pleistocene. This occurrence resulted in the evolution of a phylogeographic break for this species to the north of the Andaman Sea.
Highlights
In the marine realm, fish are abundant and ubiquitous and observed levels of genetic differentiation among populations are often low [1]
All 342 individuals sampled from 23 localities amplified successfully for the cytochrome b (Cyt b) gene and a final sequence length of 1140 bp was obtained after alignment and editing of ambiguous sequences revealing 241 unique haplotypes
The first cluster comprised all samples from the Strait of Malacca, South China Sea, Sulu Sea and Celebes Sea and the Andaman Sea, while the second contained the western Indian Ocean population of Bandar Abbas
Summary
Fish are abundant and ubiquitous and observed levels of genetic differentiation among populations are often low [1] This pattern results from combined effects of large spawning population sizes that limit genetic drift effects, the apparent absence of physical barriers to dispersal for many species in their environment and presence of highly dispersive life history stages that contribute to high rates of gene flow among populations [2]. Three major groups were detected; a north-central group comprised of northwestern Taiwan and northern Vietnam; a southwestern group in southern Vietnam; and a southern group that included the central Philippines Differentiations among these regions were attributed to limitations on gene flow that result from the impacts of sea surface currents. Late Pleistocene population expansions were hypothesized to have contributed to the reported population structure in this species
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