A comparison of maternal and temperature effects on sex, size, and growth of hatchlings of the Magdalena river turtle (Podocnemis lewyana) incubated under field and controlled laboratory conditions

Published source details Paez V.P., Correa J.C., Cano A.M. & Bock B.C. (2009) A comparison of maternal and temperature effects on sex, size, and growth of hatchlings of the Magdalena river turtle (Podocnemis lewyana) incubated under field and controlled laboratory conditions. Copeia, 2009, 698-704.
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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

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

A study in 2005–2007 in laboratory conditions in Colombia (Paez et al. 2009) found that higher incubation temperatures increased Magdalena river turtle Podocnemis lewyana hatching success, and that females were only produced above a temperature threshold. In the first year, eggs incubated at 33.0°C had a higher hatching success rate (28 of 29, 97% eggs hatched) than eggs incubated at 28.0°C (14 of 38, 37% eggs hatched) and all hatchlings at both temperatures were male. In the second year, five of 10 eggs (50%) incubated at 33.4°C and seven of seven eggs (100%) incubated at 34.7°C produced female hatchlings. The authors reported that nests monitored in the field showed a similar pattern, with the coldest nests having lower hatching rates (see original paper for details). In 2006, river turtle eggs were obtained from 28 nests and incubated in a laboratory at: 28.0°C (38 eggs), 29.5°C (43 eggs), 32.0°C (39 eggs) and 33.0°C (29 eggs). In 2007, river turtle eggs were obtained by inducing four female river turtles using an injection of oxytocin and incubated at: 33.4°C (14 eggs) and 34.7°C (13 eggs). Eggs were monitored through to hatching. Only hatching success data from 2006 laboratory eggs are included as the authors reported that the use of oxytocin to obtain eggs in 2007 may have affected hatching rates. Natural nests were monitored in the field in 2005 (8 nests) and 2006 (11 nests) for incubation temperature and hatching success.

(Summarised by: Katie Sainsbury)