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Temperature Dependent Sex Determination in Sea Turtles
Edward A. Standora and James R. Spotila
Vol. 1985, No. 3 (Aug. 5, 1985), pp. 711-722
Stable URL: http://www.jstor.org/stable/1444765
Page Count: 12
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Temperature dependent sex determination (TSD) has been demonstrated for loggerhead (Caretta caretta), green (Chelonia mydas), leatherback (Dermochelys coriacea) and olive ridley (Lepidochelys olivacea) turtles. Molecular mechanisms responsible for this phenomenon are unknown. Review of the literature suggests three processes which may be involved: (1) H-Y antigen may be an organizing factor for the heterogametic gonad, (2) Sex reversal may occur in genotypic males or females, (3) Specific DNA sequences such as the satellite DNA component found in some snakes may be altered in their expression or behavior as a movable or controlling element. Available data support the third hypothesis. At Tortuguero, Costa Rica, green turtle nests on the open beach produce mainly females while those under vegetation produce 94% male hatchlings. In nests incubating at pivotal temperatures, metabolic heating results in female hatchlings at the center of the clutch and male hatchlings along the periphery. Using known pivotal temperatures and data on the temperatures of nesting beaches we compute the primary sex ratios for several populations of sea turtles. All of these are biased towards females. Finally, TSD is proposed as a major factor in the extinction of dinosaurs.