Abstract:
To assess patterns of connectivity among populations of an Indo-Pacific reef fish, we surveyed mtDNA of the bigscale soldierfish Myripristis berndti (Holocentridae), which is concentrated on reefs at intermediate depths, but occurs to at least 160 m. Our multi-scale approach included sampling at 11 sites spanning the entire range of the species from the western Indian Ocean to the eastern Pacific, across 240° of longitude (total N = 278), and 9 islands throughout one of the largest and most isolated archipelagos, the Hawaiian Islands (subtotal N = 147). Analysis of cytochrome b sequences demonstrated the following: (1) common haplotypes are shared among all sample localities, (2) there is modest population structure across the entire species range (Öst = 0.211; p < 0.001), (3) there is no structure among the Hawaiian Islands (Öst = 0.0004; p = 0.4107), and (4) there is no structure across the central-west Pacific (Öst = -0.007, p = 0.634). Population separations across the East Pacific Barrier were significant (overall Öst = 0.278, p < 0.001; pairwise range Öst = 0.107 to 0.424), yet significantly weaker than those across the Indo-Pacific Barrier (overall Öst = 0.583, p < 0.001; pairwise range Öst = 0.329 to 0.810; Mann-Whitney U-test, p < 0.001). When grouped by major biogeographic province, populations showed no difference within the central-west Pacific (Öst = -0.007, p = 0.634), within the Indian Ocean (Öst = -0.027, p = 0.528), or within the east Pacific (Öst = -0.061, p = 0.920). Mismatch distributions and coalescence analysis indicated a rapid population expansion on the order of ~500 000 yr before present (range 300 000 to 106 yr depending on mutation rate). Despite having a vast distribution and broad depth range, M. berndti shows the genetic signatures of a population bottleneck and recovery similar to shallow reef specialists that were displaced or extirpated during glacial maxima. Overall, the mtDNA data indicated a dispersal capability in M. berndti which far exceeds that of typical reef fishes. While recent genetic studies demonstrate limited larval dispersal in some reef fishes, it is clear that others, including soldierfishes, are extensive dispersers.
