Genetic differentiation across eastern Pacific oceanographic barriers in the threatened seahorse <Emphasis Type="Italic">Hippocampus ingens</Emphasis>

Understanding the population structure and evolutionary history of the eastern Pacific seahorse Hippocampus ingens is critical for the effective management of this threatened species. Life history characteristics of H. ingens (site fidelity and brooding of young) may limit gene flow and lead to population differentiation. A recent study analyzing conserved fragments of the mitochondrial cyt b and control region found no population structure. We re-assess this conclusion with a phylogeographic analysis of relationships among 115 individuals of H. ingens over a broader geographic range (San Diego Bay in California, Gulf of California, Central America, Ecuador, and Peru) based on a more variable 428 base pair fragment of the control region. This expanded analysis affirms low overall nucleotide diversity relative to other seahorses (θ_π = 0.004), and shows evidence of a recent bottleneck and population expansion since the middle Pleistocene. AMOVA analysis shows moderate overall population structure (Φ_ST = 0.10, P val = 0.00), and pairwise Φ_ST estimates indicate structure between the Gulf of California and all Pacific coast localities. Knowledge of population structure in H. ingens may improve conservation efforts by identifying evolutionarily important management units, and could determine source regions in the continuing trade of seahorses for traditional Chinese medicine. The level of genetic divergence observed between the Gulf of California and all other localities sampled may distinguish the Gulf as a separate management unit. Additional phylogeographic research with more quickly evolving genetic markers and targeted sampling at the mouth of the Gulf of California is warranted to inform strategies for conservation of this threatened seahorse.