Effect of incubation temperature and substrate moisture on embryonic development, hatchling phenotypes and post-hatching growth in the Reeves' Turtle, Mauremys reevesii

Abstract

Background: Reeves' Turtles (Mauremys reevesii) are economically important in aquaculture in China. Understanding the effects of incubation temperature and substrate moisture on embryos and hatchlings is of great significance for improving the artificial culture of M. reevesii. However, available studies have not yet determined the thermal and hydric optima for M. reevesii eggs, and the potential interaction between the two factors.

Methods: In this study, eggs of M. reevesii were incubated at five temperature levels (23, 26, 29, 32 and 35 °C, fluctuation range ± 0.5 °C). In each temperature level, there were three substrate moisture levels (1:0.5, 1:0.9 and 1:1.2, weight ratio of vermiculite to water). Thus, a total of 15 combinations of temperature and moisture were used to examine the effects of incubation temperature and substrate moisture on incubation duration, hatching success, hatchling phenotypes, post-hatching growth and hatchling survival.

Results: Substrate moisture did not significantly affect most development parameters (except incubation duration and carapace width of hatchlings). Eggs incubated at low moisture level (1:0.5) had a longer incubation duration and produced hatchlings with smaller carapace widths than those incubated at medium (1:0.9) or high (1:1.2) moisture levels. Incubation temperature had a significant effect on incubation duration, hatching success, hatchling phenotypes and hatchling survival. Incubation duration decreased as incubation temperature increased. Eggs incubated at 23, 26 and 29 °C showed higher hatching success than those incubated at 32 and 35 °C. Hatchlings incubated at 32 °C were smaller in body size and mass than those incubated at 23, 26 and 29 °C. At 12 months of age, incubation temperature had no long-lasting effect on body mass, but hatchlings incubated at 23 and 35 °C had lower survival rates than those incubated at 26, 29 and 32 °C. For the development of embryos and hatchlings, the interaction between incubation temperature and substrate moisture was not significant.

Conclusions: Our results indicate that incubation temperature has a significant influence on the development of embryos and hatchlings of M. reevesii, while substrate moisture only significantly affects the incubation duration and carapace width of hatchlings. The combination of an incubation temperature of 29 ± 0.5 °C and a substrate moisture level of 1:1.2 represented optimal incubation conditions in this experiment. Such incubation conditions are helpful in obtaining higher hatching success, shorter incubation duration and higher survival rates for this aquaculture species.

Keywords: Hatchling phenotypes; Incubation temperature; Mauremys reevesii; Post-hatching growth; Substrate moisture.

Figure 1. Body mass of hatchlings incubated from different incubation temperature and substrate moisture at 1 month of age in Mauremys reevesii.

Figure 2. Body mass of hatchlings incubated from different incubation temperature and substrate moisture at 2 month of age in Mauremys reevesii.

Figure 3. Body mass of hatchlings incubated from different incubation temperature and substrate moisture at 3 month of age in Mauremys reevesii.

Figure 4. Body mass of hatchlings incubated from different incubation temperature and substrate moisture at 12 month of age in Mauremys reevesii.

Figure 5. Venn diagram for two explanatory variables.

The results of variance partitioning analysis to assess the response of incubation temperature and substrate moisture to incubation duration and carapace width of hatchling turtles.