Embryonic temperature affects metabolic compensation and thyroid hormones in hatchling snapping turtles

Area of Science:

• Comparative physiology
• Developmental biology
• Herpetology

Background:

• Adult vertebrate temperature acclimation alters metabolic physiology.
• Metabolic compensation during early development is poorly understood.
• Reptile embryonic temperatures influence sex determination (TSD).

Purpose of the Study:

• Investigate the effect of egg incubation temperature on hatchling snapping turtle resting metabolic rate (RMR) and thyroid hormone levels.
• Differentiate the impacts of temperature and sex on these physiological traits.
• Explore the role of thyroid hormones in metabolic compensation.

Main Methods:

• Incubated snapping turtle eggs at four temperatures (21.5, 24.5, 27.5, 30.5°C) to produce specific sex ratios.
• Measured hatchling RMR at common temperatures (25°C or 31°C).
• Assayed blood thyroid hormone levels (thyroxine) and administered triiodothyronine to assess its role.

Main Results:

• Hatchling RMR negatively correlated with egg temperature; turtles from cooler eggs had 160% higher RMR than those from warmer eggs.
• Thyroid hormone levels showed a similar negative correlation; thyroxine levels were 220% higher in hatchlings from cooler eggs.
• Triiodothyronine administration to eggs increased hatchling RMR by 31% compared to controls, supporting thyroid hormone's role.

Conclusions:

• Egg temperature induces positive metabolic compensation in snapping turtles, mediated by thyroid hormones.
• Embryonic temperature and resulting sex influence hatchling metabolic physiology and thyroid hormone levels.
• These temperature- and sex-linked physiological differences are crucial for understanding TSD ecology and evolution.