Thermal fluctuations affect embryonic physiology in a tropical agamid lizard

Area of Science:

• Herpetology
• Climate Change Biology
• Developmental Physiology

Background:

• Climate change is increasing global temperatures and thermal variability.
• Ectothermic reptile embryos are particularly vulnerable to thermal stress due to limited thermoregulation and absence of parental care.
• Existing incubation studies often use constant temperatures, failing to represent natural thermal fluctuations experienced by tropical reptiles.

Purpose of the Study:

• To investigate the effects of constant versus fluctuating incubation temperatures on embryonic physiology, development, and hatchling characteristics.
• To assess the vulnerability of tropical reptile embryos to realistic thermal regimes.
• To compare the outcomes of constant and fluctuating temperature incubations in the Indian rock agama (Psammophilus dorsalis).

Main Methods:

• Indian rock agama eggs were incubated under five different thermal regimes: constant 25°C, 30°C, 35°C, and fluctuating regimes F2 (25-30°C) and F3 (25-30-35°C).
• Embryonic heart rate, egg mass gain, development time, hatching success, and hatchling size were monitored.
• Mortality rates under different temperature conditions were recorded.

Main Results:

• Constant 35°C incubation resulted in complete embryonic mortality.
• The warmest fluctuating regime (F3) led to dampened embryonic heart rate, accelerated egg mass gain, and reduced incubation duration.
• Hatching success and hatchling size were significantly lower under the F3 fluctuating regime compared to others, indicating negative impacts of thermal variability.

Conclusions:

• Incubation temperature variability significantly impacts reptilian embryonic development and fitness.
• Constant temperature incubations may underestimate the detrimental effects of climate change on tropical reptiles.
• Utilizing fluctuating temperature regimes is crucial for accurately assessing the climate vulnerability of reptile populations.