Genetic diversity and population structure of Indo-Pacific sailfish Istiophorus platypterus in the eastern Pacific

Population genetics provides information for the management and conservation of species, because it supports the delimitation of population units. A mitochondrial DNA marker was used to determine the genetic structure of the sailfish Istiophorus platypterus at four locations in Mexico (Mazatlán, Colima, Acapulco, Oaxaca) and one location in Ecuador. We analyzed 250 nucleotide sequences of the mitochondrial control region, where 134 haplotypes were identified. Genetic diversity was relatively low in relation to other regions in the world, and other billfish species. Analysis of molecular variance indicated that genetic differences were significantly different from zero (P = 0.029), although the Φ_ST value (0.0061) was very low. Pairwise comparisons of Φ_ST indicated that the difference was attributable mainly to individuals of Ecuador, which were statistically different from those at other sampling sites. However, the genetic structure in this species could not be inferred using Bayesian analysis. Furthermore, a test of isolation by distance showed significant correlation between genetic distance and geographic distance. Phylogeographic analysis revealed a distribution of haplotypes with a star-type pattern, and mismatch distribution showed a unimodal pattern for the five sampled areas, indicative of recent demographic expansion. We estimated that the beginning of the sudden expansion happened between 80,000 and 215,000 years ago. Our results did not support a clear pattern of genetic differentiation. Capture of this species occurs in several countries, and the overall management of the resource could depend on local efforts. Further sampling is need, and additional analysis using molecular markers with high resolution (microsatellites, SNPs) must be implemented in order to gain a more robust understanding of sailfish population structure in the eastern Pacific.