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Long‐term panmixia in a cosmopolitan I ndo‐ P acific coral reef fish and a nebulous genetic boundary with its broadly sympatric sister species
Author(s) -
Horne J. B.,
Herwerden L.
Publication year - 2013
Publication title -
journal of evolutionary biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.289
H-Index - 128
eISSN - 1420-9101
pISSN - 1010-061X
DOI - 10.1111/jeb.12092
Subject(s) - panmixia , biology , phylogeography , sympatric speciation , population , ecology , biological dispersal , coral reef fish , metapopulation , genetic structure , coral reef , genetic variation , phylogenetics , demography , genetics , sociology , gene
Phylogeographical studies have shown that some shallow‐water marine organisms, such as certain coral reef fishes, lack spatial population structure at oceanic scales, despite vast distances of pelagic habitat between reefs and other dispersal barriers. However, whether these dispersive widespread taxa constitute long‐term panmictic populations across their species ranges remains unknown. Conventional phylogeographical inferences frequently fail to distinguish between long‐term panmixia and metapopulations connected by gene flow. Moreover, marine organisms have notoriously large effective population sizes that confound population structure detection. Therefore, at what spatial scale marine populations experience independent evolutionary trajectories and ultimately species divergence is still unclear. Here, we present a phylogeographical study of a cosmopolitan I ndo‐ P acific coral reef fish N aso hexacanthus and its sister species N aso caesius , using two mt DNA and two nDNA markers. The purpose of this study was two‐fold: first, to test for broad‐scale panmixia in N . hexacanthus by fitting the data to various phylogeographical models within a B ayesian statistical framework, and second, to explore patterns of genetic divergence between the two broadly sympatric species. We report that N . hexacanthus shows little population structure across the I ndo‐ P acific and a range‐wide, long‐term panmictic population model best fit the data. Hence, this species presently comprises a single evolutionary unit across much of the tropical I ndian and P acific O ceans. N aso hexacanthus and N . caesius were not reciprocally monophyletic in the mt DNA markers but showed varying degrees of population level divergence in the two nuclear introns. Overall, patterns are consistent with secondary introgression following a period of isolation, which may be attributed to oceanographic conditions of the mid to late Pleistocene, when these two species appear to have diverged.