Local genetic structure within two rookeries of Chelonia mydas (the green turtle).

We used multilocus minisatellite DNA fingerprinting to examine the local genetic structure within nesting populations of green turtles (Chelonia mydas) in Tortuguero, Costa Rica and Melbourne, Florida, USA. In the Tortuguero population, there was a significant negative correlation between genetic similarity of pairs of nesting females and the distance between their nest sites both within years (r2 = 0.273; P < 0.001) and between years (r2 = 0.578; P < 0.001). Of the 122 female pairs scored for Tortuguero, 12.3 per cent had genetic similarity values resembling those of mother-offspring pairs. In the Melbourne population, however, no relationship between genetic similarity and distance was found (r2 = 0.017; P = 0.075). The distance-related genetic structure of the Tortuguero population indicates that these females exhibit low levels of dispersal from natal sites, and that nestmates return independently to nest near their natal sites. The lack of a similar structure in the Melbourne population suggests that females from this population may not return to natal sites with comparable precision. High levels of mortality among nests, hatchlings or maturing turtles produced in the Melbourne rookery may also be responsible for the absence of distance-related local genetic structure.