Effect of Temperature on Development: The Case of the Malayan Snail-Eating Turtle Malayemys macrocephala

Abstract

The embryonic development in several freshwater turtles is dependent on the incubating temperature. Different incubating temperature can induce significant difference in sex ratios among turtle populations with temperature dependent sex determination. The Malayan snail-eating turtle, Malayemys macrocephala, is a native freshwater turtle commonly found in rice fields of Thailand. Previous morphometric analysis on this species suggested a temperature-dependent pattern of sex determination. This study aimed to examine effect of temperature on gonadal development of M. macrocephala using histological analysis. Turtle eggs were collected during December 2011 to February 2012 from rice fields in Phra Nakhon Si Ayutthaya province in the central part of Thailand and incubated in the laboratory at 26 °C, 29 °C and 32 °C. Results from sex identification based on gonadal structure and statistical analyses of sex ratio confirm prior observations that incubation at low temperature (26 °C) produced male-biased sex ratio, while incubation at high temperature (32 °C) produced female-biased sex ratio. Incubation at 29 °C resulted in 1 male: 1 female sex ratio, suggesting that this incubating temperature is a pivotal temperature of M. macrocephala. A 3 × 3 contingency table analysis reveals a significant association between incubating temperature and the stage of gonadal development. Interestingly, testicular development was more advanced at 32 °C than other temperatures, while developmental stage of the ovaries was more advanced at 29 °C than other temperatures. This suggested that incubating temperature can also induce significant difference in gonadal development of the freshwater turtle.