Pivotal temperature for loggerhead turtles (Caretta caretta) from Kyparissia Bay, Greece

Pivotal temperature (the constant temperature giving 50% of each sex) for two clutches of loggerhead sea turtles (Caretta caretta) from Kyparissia Bay, Greece, was 29.3°C. Pivotal incubation duration (the time from laying to hatching giving 50% of each sex) was 52.6 days. These values are close to those obtained for this species in Brazil and the United States, providing further evidence that these characteristics are relatively conservative in different populations. Methodological differences between different experiments and limitations on accuracy of equipment make the detection of small differences problematic. Comparison of incubation durations in the field with the pivotal durations obtained here suggest that hatchling sex ratio on some Mediterranean beaches is female biased but probably varies considerably within this region.

Hydric environment and sex determination in the flatback turtle (Natator depressus Garman) (Chelonia : Cheloniidae)

Eggs of Natator depressus (from eastern Queensland, Australia) were incubated at a constant temperature of 29.5˚C on vermiculite substrate with three different moisture levels: wet (~–180 kPa), intermediate (~–1200 kPa) and dry (~–2000 kPa). The male : female ratios on wet, intermediate and dry substrates were 8 : 7, 5 : 5 and 5 : 8 respectively. Sex determination was not influenced by the hydric environment but was significantly affected by different clutches. A clutch with smaller eggs appeared to produce a higher proportion of females. The pivotal temperature was close to 29.5˚C, with a possibly narrow transitional temperature range of 1˚C. Visual designation of sex was confirmed (100%) by histological examination. Hatching success and the incubation duration were not influenced by the hydric environment.

Pivotal temperature and predicted sex ratios for hatchling hawksbill turtles from Brazil

Like all other species of sea turtle, the hawksbill turtle (Eretmochelys imbricata) exhibits temperature-dependent sexual differentiation, with high incubation temperatures producing females and low temperatures producing males. Relatively little is known about the sex ratios of hatchlings produced by nesting populations of hawksbill turtles. Here we estimate the overall seasonal sex ratios of hatchling hawksbill turtles produced in Bahia, Brazil, during 6 nesting seasons, based on incubation durations, pivotal temperature, and pivotal incubation duration. The overall sex ratio of hatchlings produced in Bahia from 1991-1992 through 1996-1997 was estimated to be >90% female, which is more female-biased than estimated sex ratios of hatchling loggerhead turtles from Bahia and Florida, U.S.A. The biological and conservation implications of skewed sex ratios are discussed.

Incubation temperature affects sexual differentiation, incubation time, and posthatching survival in desert tortoises (Gopherus agassizi)

Eggs of captive desert tortoises. Gopherus agassizi, incubated at six temperatures (25, 27, 28, 29, 29.4, and 31 °C) produced 107 specimens. Eggs incubated at 31 °C resulted in a male to female sex ratio of 5:7; all other incubation temperatures resulted in males only. Histological examination of gonads revealed that the testes of newly hatched to 3-month-old individuals showed incomplete and poorly developed seminiferous tubules. Female gonads showed a thickened cortex. Incubation times were longer at lower temperatures. Both hatching success and hatchling survivorship were lower at lower incubation temperatures. We confirm that temperature-dependent sex determination occurs in desert tortoises and that the pivotal temperature is between 31 and 32 °C.