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Heat Waves Increase Risk for Unhatched Geckos

While ectothermic reptiles can raise their body temperature by basking in the sun, their future may not be so sunny as environmental temperatures continue rising. Heat waves have become more common in recent decades and are predicted to increase in frequency in the future, and Dr Jonathan Webb of the University of Technology, Sydney says that adult reptiles will be able to weather the warmer weather but is concerned for embryos and young hatchlings. “Developing lizard embryos cannot thermoregulate and may experience thermally stressful temperatures in natural nests during summer,” Webb suggests.

Since flies that develop in high temperatures seem to cope better in extreme conditions, Webb and his colleagues incubated the eggs of tiny velvet geckos (Amalosia lesueurii) at high (14–37°C) and moderate (10–33°C) temperatures to find out how heat waves might affect the developing geckos. The research has been published in the Journal of Experimental Biology.

While the eggs incubated at higher temperatures hatched 27 days earlier, their head start didn’t give them an advantage when the temperature fluctuated. When the researchers turned the hatchlings on their backs after being warmed or cooled, those that had been incubated in hot nests were less able to right themselves at extreme temperatures than the geckos that had been incubated at lower temperatures. The hot-incubated geckos became incapacitated at temperatures below 6.2°C and above 38.7°C, while the animals that had been incubated at lower temperatures were more robust, only failing to right themselves below 5.7°C and above 40.2°C.

When the team measured the temperatures under the rocks that the youngsters prefer to use for shelter, they could reach a sizzling, and potentially fatal, 50°C. However, crevices in which the hatchlings shelter only reached 33°C.

Webb points out that this will pose a problem for hatchlings that emerge early. “Shuttling between rocks and shady crevices may expose them to predators, compromising their survival,” he says. Hence gecko embryos incubated during a heat wave are less prepared for scorching temperatures and will be more vulnerable to predation.