Temperature sex determination, incubation duration, and hatchling sexual dimorphism in the Espanola giant tortoise (Chelonoidis hoodensis) of the Galapagos Islands

Published source details Sancho A., Gutzke W.H.N., Snell H.L., Rea S., Wilson M. & Burke R.L. (2017) Temperature sex determination, incubation duration, and hatchling sexual dimorphism in the Espanola giant tortoise (Chelonoidis hoodensis) of the Galapagos Islands. Amphibian & Reptile Conservation, 11, 44-50.
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This study is summarised as evidence for the following.

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	Alter incubation temperatures to achieve optimal/desired sex ratio: Tortoises, terrapins, side-necked & softshell turtles Action Link

Alter incubation temperatures to achieve optimal/desired sex ratio: Tortoises, terrapins, side-necked & softshell turtles

A study in 1986 in a captive rearing facility in Galápagos, Ecuador (Sancho et al. 2017) found that less than half of artificially incubated Española giant tortoise Chelonoidis hoodensis eggs hatched in captivity and that the sex ratio was temperature dependent. Results were not statistically tested. Española giant tortoise eggs artificially incubated at 25.5°C had a hatching success of 16% and 10 of 11 (91%) sexed hatchlings were male. Eggs incubated at 29.5°C had a hatching success of 40% and five of 15 (33%) sexed hatchlings were male. No eggs artificially incubated at 33.5°C hatched successfully. In 1986, giant tortoise eggs laid in captivity as part of a head-starting programme were incubated at three different temperatures: 25.5, 29.5 and 33.5°C (67 eggs/temperature, 189 total eggs). Eggs were placed in plastic boxes with damp vermiculite, covered and put in incubation chambers. Hatchlings were sexed by direct observation, examination of dead hatchlings’ gonads (35 individuals) or key-hole surgery (15 individuals). Data from six hatchlings that hatched earlier in the season in the same facility were included in the results.

(Summarised by: Katie Sainsbury)