Genetic Identification of an isolated seahorse population in a saltwater lake on Eleuthera Island, Bahamas

Presented by Emily Rose

Emily Rose, Heather Masonjones, and Adam G. Jones

Previous work in a saltwater lake, Sweetings Pond, on Eleuthera Island, Bahamas, identified the presence of seahorses belonging to the species Hippocampus reidi in the 1980s. Additional samples were collected from Sweetings Pond during the summer of 2014 for species identification using morphological and genetic analyses. Morphological attributes of the seahorses from Sweetings Pond were compared to the two species of seahorses with overlapping distributions in the Bahamas, H. reidi and H. erectus, but were not informative enough to identify the collected specimens. However, distinct morphological characteristics were identified in the Sweetings Pond population. Next, we turned to molecular markers and utilized a mitochondrial gene (cytochrome b) and a nuclear gene (S7) to identify the species of the Sweetings Pond seahorses. Phylogenetic analyses showed that these samples were nested within the Hippocampus erectus clade for both genes. These results indicate that the Sweetings Pond seahorses are an isolated population of Hippocampus erectus with a more even torso to tail body ratio compared to other members of the H. erectus clade and other tail-biased seahorse species found in their geographic range. As a result of a weak or nonexistent current, no fishing pressures, and a relatively predator-free environment in the lake, this pond presents a unique opportunity to study an isolated population of seahorses evolving with relaxed selection pressures.