Alter incubation temperatures to achieve optimal/desired sex ratio: Sea turtles

Overall effectiveness category Awaiting assessment
Number of studies: 1
Share Tweet Email

View assessment score

How is the evidence assessed?

Effectiveness

not assessed
Certainty

not assessed
Harms

not assessed

Calculating overall effectiveness category

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.}

Study locations

Key messages

One study evaluated the effects of altering incubation temperatures to achieve optimal/desired sex ratios on sea turtles. This study was in Canada.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Reproductive success (1 study): One replicated study in Canada reported that hatching success of two clutches of artificially incubated green turtle eggs was 8% and 62%.

BEHAVIOUR (0 STUDIES)

OTHER (1 STUDY):

Offspring sex ratio (1 study): One replicated study in Canada found that incubating green turtle eggs at higher temperatures resulted in more females hatchlings.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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
Referenced paper
Godfrey M.H. & Mrosovsky N. (2006) Pivotal temperature for green sea turtles, Chelonia mydas, nesting in suriname. The Herpetological Journal, 16, 55-61.

Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Reptile Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Breed reptiles in captivity: Tuatara Action Link	Awaiting assessment	1	Synopsis Link
Freeze sperm or eggs for future use Action Link	No evidence found (no assessment)	0	Synopsis Link
Use hormones and/or other drugs during captive-breeding programmes to induce reproduction/birth Action Link	Awaiting assessment	9	Synopsis Link