GENETIC DIFFERENTIATION BETWEEN PARAPATRIC NEARSHORE AND OFFSHORE POPULATIONS OF THE BOTTLE-NOSED-DOLPHIN

The existence of nearshore and offshore populations of the bottlenose dolphin has been documented throughout its range. In several cases the two regional forms have been shown to be morphologically distinct, al though there is considerable overlap for most characters. The populati ons off the eastern coast of North America have been the subject of a long-term programme of research on their distribution and movements. I n this study, we compare mitochondrial and nuclear genetic markers bet ween dolphins classified as either nearshore or offshore type. These p utative populations were found to be distinct at both nuclear and mito chondrial genetic markers. Further, the level of variation among the n earshore dolphins was reduced compared with the offshore population. A broader geographical comparison suggests a shared lineage between off shore dolphins from the western North Atlantic and both offshore and n earshore dolphins from the eastern Atlantic. These results are consist ent with local differentiation based on habitat or resource specializa tion in the western North Atlantic, and suggest differences in the cha racter of the nearshore/offshore distinction in different parts of the world.