Genetic Analysis of Populations of the Cownose Ray, Rhinoptera bonasus in the Chesapeake Bay and Florida Coast

Abstract

In the spring and early summer, large schools of cownose rays, Rhinoptera bonasus, migrate into the Chesapeake Bay to forage, give birth to pups, and breed. Rays move throughout the meso- and polyhaline portions of the Bay, but it is not currently known if they form genetically isolated subpopulations during this time. I analyzed DNA sequence variation from portions of two variable mitochondrial genes cytochrome b and cytochrome c oxidase I in samples collected from two sites in the Chesapeake Bay (St. George Island, MD, and Reedville, VA) and from Tampa Bay, FL. Tooth series were also recorded for both sites in the Bay, as it has been reported as a method to distinguish between two species, R. bonasus and a species normally found off the coast of Brazil, R. brasiliensis. Results show that there is a statistically significant (p <0.05) difference in the distribution of haplotypes between the two Bay subpopulations as well as a difference between Chesapeake and Tampa Bay populations. The Florida and Reedville population share a haplotype that is present in substantial frequencies (34% and 23%, respectively) but absent from the St. George Island population. These results suggest that the two Chesapeake locations attract different southern source populations each summer. The tooth series data in conjunction with the haplotype results suggest that it is not a reliable feature to distinguish between R. bonasus and R. brasiliensis. Portions of three mitochondrial genes were sequenced to characterize the evolutionary relationship of Rhinopera bonasus to other Chondrichthyans. Phylogenetic trees were constructed using Neighbor-Joining methods for the 12S rRNA, 16S rRNA, and NADH-2 genes. Results confirm that Rhinoptera bonasus is most closely related to other species in order the Myliobatiformes.