A team of researchers working in China has proven that the three-keeled pond turtle embryo is capable of moving itself towards or away from a heat source in order to warm itself or cool down. In their paper published in the journal Biology Letters, the team describes how they subjected turtle embryos to various heat scenarios while monitoring their movements inside their shells to show that the turtles were directing their own actions while still inside their eggs.
Turtles, as most are aware, are cold-blooded animals. They regulate their body temperature by moving themselves to warmer or cooler places. In this new study, the researchers found the same ability applies to turtles while still in their shell.
Biologists have known since 2011 that at least some turtle embryos move about in their shell in response to external heat sources. Another team in China had discovered this ability and had published a paper describing their results. What that team wasn’t able to say for sure, though, was whether the turtle embryos were moving themselves or if fluids within the shell were causing the movement. In this new effort, the research team sought to find the answer to that question.
The team set 125 turtle eggs (in groups of five) in incubators set at 26 °C. Then four of the five groups were subjected to various degrees of heat applied at one end of the eggs. The team also set up bright lights next to the eggs that allowed them to see the silhouettes of the embryos inside as they moved. In all but the control group, the team observed that the embryos moved away from the heat source, thus confirming the findings of the team in 2011.
To ascertain whether the embryos were moving themselves or were simply being carried by heated fluid, the researchers ran another similar experiment. This time they allowed 41 embryos to develop naturally for ten days, whereupon, they killed half of them using an injected chemical. After applying heat and waiting for a week, they cracked open the eggs and found that only those turtle embryos still alive had moved away from the source. This they claim, proves that the embryos moved themselves intentionally.