Study

The role of incubation temperature and clutch effects in development and phenotype of head-started western pond turtles (Emys marmorata)

  • Published source details Geist N.R., Dallara Z. & Gordon R. (2015) The role of incubation temperature and clutch effects in development and phenotype of head-started western pond turtles (Emys marmorata). Herpetological Conservation and Biology, 10, 489-503.

Actions

This study is summarised as evidence for the following.

Action Category

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

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

    A replicated, randomized study in 2008–2009 in laboratory conditions in California, USA (Geist et al. 2015) found that altering incubation temperatures of western pond turtle Actinemys marmorata eggs resulted in variable hatching success, and that no female hatchlings were produced at lower temperatures. Hatching success varied with temperature, with the highest reported success rate at 29°C (26 of 28, 93%) and the lowest at 31°C (3 of 7, 43%). Hatching success at other temperatures (26, 27, 28 or 30°C) ranged from 68–82%. Eggs at 26–27°C produced all male hatchlings and those at 28–29°C were highly skewed towards males (28°C: 92% males; 29°C: 85% males), while those at 30°C produced all females. In 2008–2009, eggs were obtained from 44 wild turtle nests. Eggs were distributed evenly between five plastic containers that were partially filled with moist vermiculite (5:1 ratio with water by volume) and incubated at constant temperatures. Five temperatures were chosen in 2008, and these were all decreased by 1°C in 2009, resulting in the following number of eggs/treatment: 15 eggs at 26°C; 28 at each of 27, 28 and 29°C; 25 at 30°C; seven at 31°C. In 2009, the sex of fifty-nine turtles was determined through a non-lethal surgical procedure that allowed gonads to be observed (see paper for details).

    (Summarised by: William Morgan)

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