Effects of temperature on gonadal development of the snail-eating turtle malayemys macrocephala

Abstract

Increase in average temperature that gradually warms the earth can change both physical and biological environments and affects survival of organisms. Reptiles, especially freshwater turtles, are considered as susceptible species since their development is dependent on incubating temperature. Current research thus aimed to examine effects of temperature on somatic and gonadal development of the snail-eating turtle, Malayemys macrocephala, a native and the most common freshwater turtles in Thailand. Turtle eggs were collected from rice fields in Bang Ban district, Phra Nakhon Si Ayutthaya province from December 2011 to February 2012. Based on 5 field surveys, a total of 712 eggs from 126 clutches of M. macrocephala were collected and transported to a laboratory. Eggs were incubated in microprocessor-controlled incubators at three different temperatures (26°C, 29°C and 32°C)and randomly dissected on weekly basis until hatch. It was found that incubation period, time from beginning of incubation until hatch, was not significantly different among temperatures (115+11, 115+20 and 109+18 days, respectively). Development of M. macrocephala was studied in reference to the standard stages of turtle development based on morphological characters. Growth patterns as indicated by stage of development and carapace length were significantly different among temperatures. At high temperature (32 °C), turtle embryos grew significantly more rapid than low temperature (26 °C) and pivotal temperature (29°C). However, embryos incubated at high temperature had a significantly higher incidence of malformation than other temperatures. Histological analysis for gonadal development showed that incubating temperature could affect differentiation of gonads into ovaries or testes as well as degree of development of the gonad, suggesting that M. macrocephala exhibits a temperature-dependent sex determination. Overall, the results indicated that incubating temperature is an important variable affecting both somatic and gonadal development of M. macrocephala. The data from this study could be used to assess the impact of global trend of temperature change and potential mitigation measure to reduce this impact on the freshwater turtle in order to conserve their natural populations.