Turtle embryos bask against the warmest side of their own eggs
Many animals, including the majority of reptiles, cannot produce their own body heat. To control their temperature, they have to use their environment. They bask in the sun to heat up and lounge in the shade to cool down. And some of them start before they’ve even hatched.
Wei-Guo Du from the Chinese Academy of Sciences has found that the embryos of soft-shelled turtles “bask” inside their eggs. “People usually think reptilian embryos are immobile,” says Du. After all, their limbs are tiny stumps and they have few places to move to. But that doesn’t stop them. Du found that the embryos can not only move, but they can snuggle up to the warmest side of their eggs.
He collected 260 eggs from a local turtle farm, placed them in individual jars and warmed them with heat lamps. The eggs were about one degree Celsius warmer on the sides closest to the lamps, and the turtles could sense this. After a few days, they had pressed up against the warmer side. When Du moved the heat lamps around, the embryos followed.
Du also buried 540 eggs in more natural nests, either in a flat field or a sloping river bank. He arranged all the eggs so the embryos were sitting in the uppermost half (he could tell where they were by shining a candle behind them and looking at the silhouette). After 20 days, the embryos in the field, with the sun warming them from directly overhead, stayed in the same position. However, the embryos buried on the slope, with the sun shining down on them at an angle, shifted towards the bank.
Do these results have any relevance to natural conditions? Du thinks so. “Most reptiles lay eggs in underground nests, which are heated by sunlight falling on the ground above,” he writes. These can create uneven temperatures within the nest – some eggs will be warmer than others and some parts of each egg will be warmer than other parts.
Soft-shelled turtle embryos can sense these differences and respond to them, basking in the warmth before they’re even hatched. “To our knowledge, no previous study has looked for this ability, presumably because embryos were thought incapable of such behaviour,” says Du.
A small difference in temperature can mean the world to a developing turtle. It can affect how quickly it grows, how big it gets, and when it hatches. Heat a turtle embryo up by one degree – the temperature difference that Du found in his experiment – and it will hatch around 4.5 days earlier. That’s 4.5 days when it won’t be a sitting duck for egg predators, and when it can escape from extremes of temperature or drought.
Mother turtles may decide where to bury the eggs, but the embryos aren’t passive. By moving about in their cramped homes, they have a small say in their own fates. Du says, “The embryo is not simply a work in progress, but is a functioning organism with surprisingly sophisticated and effective means of affecting its own destiny.”
This discovery raises a tantalising possibility. For many reptiles, the temperature of the egg determines the sex of the babies. In some turtles, if eggs are incubated at 22.5 to 27 degrees, the babies will be all male. If they’re incubated at 30 degrees, they’ll all be female. Temperatures in the middle will yield a mixed-sex clutch. For the moment, Du doesn’t know if the soft-shelled turtle relies on temperature in this way, or if other reptiles that do rely on temperature can move about in their own eggs. If either statement is true, then they may be able to control their own sex.
Reference: Du, Zhao, Chen & Shine. 2011. Behavioral thermoregulation by turtle embryos. PNAS http://dx.doi.org/10.1073/pnas.1102965108
More on reptiles and temperature:
- Sex runs hot and cold – why does temperature control the gender of Jacky dragons
- Prehistoric sea dragons kept themselves warm
- Pocket Science – chameleons hunt with cold-proof tongues and zebrafish babies go blind at night
- Measuring dino fitness – more evidence that two-legged dinosaurs were warm-blooded
- How prehistoric sea monsters sorted males from females
- When the heat is on, male dragons become females
Go Further
Animals
- These 'trash fish' are among Earth's most primitive animalsThese 'trash fish' are among Earth's most primitive animals
- These photos are works of art—and the artists are bugsThese photos are works of art—and the artists are bugs
- The epic migration of a 6-foot long, 200-pound catfishThe epic migration of a 6-foot long, 200-pound catfish
- Frans de Waal, biologist who studied animal emotion, dies at 75Frans de Waal, biologist who studied animal emotion, dies at 75
Environment
- Are synthetic diamonds really better for the planet? The answer isn't clear-cut.Are synthetic diamonds really better for the planet? The answer isn't clear-cut.
- This year's cherry blossom peak bloom was a warning signThis year's cherry blossom peak bloom was a warning sign
- The U.S. just announced an asbestos ban. What took so long?The U.S. just announced an asbestos ban. What took so long?
- The most dangerous job? Inside the world of underwater weldersThe most dangerous job? Inside the world of underwater welders
- The harrowing flight that wild whooping cranes make to surviveThe harrowing flight that wild whooping cranes make to survive
History & Culture
- Meet the powerful yokai that inspired the demon king in ‘Demon Slayer’Meet the powerful yokai that inspired the demon king in ‘Demon Slayer’
- A surprising must-wear for European monarchs? Weasels.A surprising must-wear for European monarchs? Weasels.
- Meet the woman who made Polaroid into a cultural iconMeet the woman who made Polaroid into a cultural icon
- Inside the observatory that birthed modern astrophysicsInside the observatory that birthed modern astrophysics
- See how Muslims celebrate Eid al-Fitr around the worldSee how Muslims celebrate Eid al-Fitr around the world
Science
- NASA smashed an asteroid with a rocket. The debris could hit Mars.NASA smashed an asteroid with a rocket. The debris could hit Mars.
- Humans really can have superpowers—scientists are studying themHumans really can have superpowers—scientists are studying them
- Why engineers are concerned about aging infrastructureWhy engineers are concerned about aging infrastructure
- The benefits of eating the peels on your fruits and veggiesThe benefits of eating the peels on your fruits and veggies
- The island of Santorini is hiding an explosive secretThe island of Santorini is hiding an explosive secret
Travel
- Play and stay in the mountains of eastern Nevada
- Paid Content
Play and stay in the mountains of eastern Nevada - This couple quit the city to grow wasabi in Japan's mountainsThis couple quit the city to grow wasabi in Japan's mountains