Alter incubation temperatures to achieve optimal/desired sex ratio: Sea turtles
Overall effectiveness category Awaiting assessment
Number of studies: 1
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Background information and definitions
Incubation temperatures (for example warmer or cooler, constant or fluctuating) can influence the sex, size, shape, colour, behaviour, movement ability and post-hatching growth of reptile hatchlings and newborns (Booth et al. 2006). Practitioners carrying out conservation activities aimed at maximising hatching success, such as relocating eggs for artificial incubation or to on-beach hatcheries, will therefore need to consider the potential impact of temperature during incubation on hatchlings and populations. Human-induced climate change may also influence the sex ratios of some species of reptiles and limit the viability of populations over time. It may be possible to counter the impacts of climate change on affected populations by managing temperatures during incubation to create appropriate sex ratios.
This action includes studies that test the impact of different temperatures on the sex ratio of reptile hatchlings or newborns. For studies that discuss the effectiveness of relocating sea turtle nests/eggs for incubation more generally, see Relocate nests/eggs for artificial incubation, Relocate nests/eggs to a nearby natural setting (not including hatcheries), and Relocate nests/eggs to a hatchery. For studies that discuss the effectiveness of captive breeding more generally, see Breed reptiles in captivity.
Due to the number of studies found, this action has been split by species group, though no studies were found for amphisbaenians. See here for: Tortoises, terrapins, side-necked & softshell turtles; Snakes & lizards; Crocodilians or Tuatara.
Booth D.T. (2006) Influence of incubation temperature on hatchling phenotype in reptiles. Physiological and Biochemical Zoology, 79, 274–281.
Supporting evidence from individual studies
A replicated study in 1995 in an artificial setting in Toronto, Canada (Godfrey & Mrosovsky 2006) found that more female green turtle Chelonia mydas hatchlings were produced at higher incubation temperatures compared to at lower temperatures. Hatching success for two clutches of eggs was 8% (7 of 90 eggs) and 62% (67 of 108 eggs). Warmer incubation temperatures produced a higher proportion of female hatchings (30.6°C: 100%; 30.0°C: 50%; 29.4°C: 47%; 28.7°C: 36%; 28.4°C: 18%; 28.2°C: 8%; 27.6°C: 0%). The pivotal temperature for determining sex of hatchlings was estimated at 29.4–30°C. In 1995, green turtle eggs were collected from two nests (90 from one nest and 108 from a second) and brought into an artificial setting and placed in an individual container on a sponge with damp vermiculite. Eggs were incubated at one of seven temperatures between 27.6°C to 30.6°C (14–48 eggs/temperature). Hatching success was assessed, and sex of hatchlings was determined by examining the gonads under a microscope.Study and other actions tested
Where has this evidence come from?
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This Action forms part of the Action Synopsis:Reptile Conservation
Reptile Conservation - Published 2021