Connectivity and structure of Atlantic green sea turtles (Chelonia mydas): A genetic perspective

The exceptional navigational skills, population biology, and historical ecosystem function of green sea turtles (Chelonia mydas) have been the focus of intense scientific interest. Even so, and despite the endangered status of marine chelonians worldwide, aspects of this species' biology essential for research and conservation purposes remain unknown. Elucidating relationships among marine chelonian populations is a global research priority (MTSG 1995). The work presented here characterizes Chelonia mydas breeding and foraging groups in the Atlantic Ocean basin employing population genetic methods. In this approach major objectives are to: (1) Determine natal origins of Western South Atlantic foraging groups; (2) Elucidate connectivity among feeding aggregations; (3) Assess subdivision among key rookeries as revealed by nuclear genetic markers; (4) Examine rarely addressed aspects of intra-population genetic structure; and (5) Consider processes impacting connectivity in Atlantic C. mydas. The study revealed feeding aggregations in Brazil are mixed stocks, drawn primarily from Ascension Island (UK)/Atol das Rocas (Brazil), as well as Suriname/Aves Island, Venezuela. Tortuguero, Costa Rica was an additional contributor at one study site, and the intriguing possibility that turtles born in Africa may be foraging in Brazil needs to be further investigated. The Almofala and Ubatuba foraging grounds are distinct from each other at mitochondrial loci, and from most other Atlantic aggregations. The results are consistent in general with a model of juvenile natal homing. Temporal and demographic structure in mitochondrial genetic variation was not detected at Ubatuba or Almofala. Weak to intermediate subdivision among Atlantic rookery groups was indicated by microsatellite analysis, with isolation by distance as a plausible constraint on gene flow among rookeries. The significance of the study derives from otherwise unobtainable insight into temporal and spatial patterns of genetic variation, as well as dispersal and migration. The research enhances basic biological knowledge of marine vertebrate population structure, with applications to migratory species worldwide.