Genotypic sex determination (GSD) and temperature-dependent sex determination (TSD) coexist in reptiles. TSD means that sex is determined after fertilization by the incubation temperature that the embryo experiences during a limited window of time, called the thermosensitive period (TSP). Most of turtles exhibit TSD and have two patterns: TSDⅠ and TSDⅡ. In TSDⅠ, females are produced at high temperatures and males at low ones. In TSDⅡ, females are produced at high and low temperatures and males at intermediate ones. In some species of turtles, such as Clemys insculpta、Emydura singnata, however, their sexes are not affected by incubation temperatures, and are determined by genotypes.
The Asian yellow pond turtle (Mauremys mutica Cantor) is a member of the family Emydidae, native to the southeastern Asia. In China, it is distributed in Guangxi, Guangdong, Hainan, Fujian, Anhui, Zhejiang, Jiangshu, and Taiwan. Owing to the higher values for food and remedy than other species of turtles, greater attention has been paid to aquaculture of the turtle. But there are not any reports of the research on sex determination in yellow pond turtle. In order to understand the sex determination pattern in yellow pond turtle, the sex phenotypes on different incubation temperature were observed and the mechanism of sex determination was analyzed firstly by using rearing propagate population in this paper. Eggs were divided into three groups (40 eggs per group) and incubated under three different temperatures, such as (25±0.5)℃, (29±0.5)℃, and (33±0.5)℃. T he embryonic developmental rates increase as the incubation temperatures rise at the three different temperatures. Cumulative temperature units (CTUs) (degree•hours) was highest at (25±0.5)℃, lowest at (29±0.5)℃, and middle at (33±0.5)℃. At (25±0.5)℃ and (29±0.5)℃, embryonic survival rate was 97.5%, but only 67.5% at (33±0.5)℃ and with 11.1% abnormality. The data indicated that higher temperature at (33±0.5)℃ could affect embryonic development, because the CTUs at (33±0.5)℃ was higher than that at (29±0.5)℃, and the survival rate was lower than that at (29±0.5)℃ and at (25±0.5)℃. The resulted females increase as the incubation temperatures rise. The percentage of females was 23.7% and 50% at (25±0.5)℃ and at (29±0.5)℃, whereas the ratio moved up to 94.7% at (33±0.5)℃. The data indicated that the sex ratios produced at (25±0.5)℃ and (33±0.5)℃ was significantly different from the sex ratios (1∶1) (p<0.005) by X2 test, and suggested that yellow pond turtle should be temperature-dependent sex determination (TSD) mechanism, and belong to the TSDⅠpattern in which females are produced at high temperatures and males at low ones. The pivotal temperature of yellow pond turtle is likely to be 29℃.