Can Reptile Embryos Influence Their Own Rates of Heating and Cooling?

Wei-Guo Du,Rajkumar S Radder,Ming-Chung Tu,Richard Shine,Andrej A Romanovsky

doi:10.1371/journal.pone.0067095

Abstract

Previous investigations have assumed that embryos lack the capacity of physiological thermoregulation until they are large enough for their own metabolic heat production to influence nest temperatures. Contrary to intuition, reptile embryos may be capable of physiological thermoregulation. In our experiments, egg-sized objects (dead or infertile eggs, water-filled balloons, glass jars) cooled down more rapidly than they heated up, whereas live snake eggs heated more rapidly than they cooled. In a nest with diel thermal fluctuations, that hysteresis could increase the embryo’s effective incubation temperature. The mechanisms for controlling rates of thermal exchange are unclear, but may involve facultative adjustment of blood flow. Heart rates of snake embryos were higher during cooling than during heating, the opposite pattern to that seen in adult reptiles. Our data challenge the view of reptile eggs as thermally passive, and suggest that embryos of reptile species with large eggs can influence their own rates of heating and cooling.

Highlights

Many physiological processes are sensitive to temperature, placing a selective premium on the ability of organisms to maintain body temperatures within optimal ranges [1]
Since the 1960’s, we have known that terrestrial reptiles control their body temperatures behaviourally and physiologically: many reptiles heat faster than they cool, by adjusting heart rates and blood flow [3,4]
Previous investigations have assumed that embryos lack the capacity of physiological thermoregulation until they are large enough for their own metabolic heat production to influence nest temperatures [8]

Summary

Introduction

Many physiological processes are sensitive to temperature, placing a selective premium on the ability of organisms to maintain body temperatures within optimal ranges [1]. Since the 1960’s, we have known that terrestrial reptiles control their body temperatures behaviourally (e.g. sun-basking [2]) and physiologically: many reptiles heat faster than they cool (hysteresis), by adjusting heart rates and blood flow [3,4]. Previous investigations have assumed that embryos lack the capacity of physiological thermoregulation until they are large enough for their own metabolic heat production to influence nest temperatures [8]. Large eggs provide the best opportunity to detect embryonic control over thermal exchange rates, because slower heating and cooling provides a greater potential selective advantage to modifying such rates, and facilitates detection of thermal hysteresis. We examined the large eggs of the Indian Python (Python molurus), the Australian Carpet Python (Morelia spilota) and the stripe-tailed ratsnake (Elaphe taeniura), to see if snake embryos are able to influence the rates at which they heat and cool

Results

Discussion

Materials and Methods