Effects of Incubation Temperature on the Embryonic Development and Hatching Success of the Western Pond Turtle (Emys marmorata)

The western pond turtle (WPT), Emys marmorata, is listed by the CA Department of Fish and Game as a Species of Special Concern in California and yet still little is known about much of its basic reproductive and developmental biology. It has been well documented that incubation temperature may affect a range of phenotypic variables in various hatchling reptiles, but few of these studies have concentrated on turtles. For this study, a sample of WPT eggs from Lake Country, California were incubated at 27, 28, 29, 30, and 31°C for the duration of their embryonic development. There was a significant reduction in hatching success at the upper and lower limits of this temperature regime, but temperature had no significant effect on hatchling weight. Incubation duration increased with incubation temperature. Additionally, endoscopic examination of the hatchlings' gonads confirmed that gender determination for this species is temperature-dependent, with a M-F pattern similar to most other emydid turtles. Clutch effects were found to influence hatchling weight and incubation duration.