Abstract
Despite decades of study, it remains difficult to predict the genetic structure of populations of marine species, even with extensive knowledge of the regional oceanography, geography, and the life history of the species. Genetic data provide key insights into population structure that cannot be otherwise inferred. To this end, phylogeographic patterns across the Line Islands were assessed in three unrelated species of reef-associated fish, Stegastes aureus , Lutjanus bohar , and Pseudanthias bartlettorum using the mitochondrial gene cytochrome oxidase I (COI). All three species show evidence of significant population differentiation, with the sharpest break separating the southernmost islands of Vostok and Millennium from the islands to the north. This pattern is broadly consistent with results of larval dispersal simulations based on available ocean current data and estimated planktonic dispersal durations for the three species. Bayesian generalized linear modeling shows correlation between geographic distance and genetic distance for L. bohar and P. bartlettorum but was unable to find a significant predictor variable for differentiation in S. aureus . While the presence of differentiated fish populations within the Line Islands is clearly demonstrated, the reasons for the apparent phylogeographic break near the southern end of the archipelago remain unclear.