Whether you walk, slither or fly, there is no job in the world like parenting. Parents are responsible for balancing the many needs of their children and deciding which of those needs are most important. Mammals are known for caring for their young, but reptiles aren’t often seen as loving parents. ASU researchers are taking a deeper look at parental care in certain snakes, and how simple behaviors have a huge impact on their young.
Zach Stahlschmidt and Jake Brashears are biology graduate students at ASU. They are studying the brooding habits of both wild pythons and pythons in the lab. Brooding means sitting on the eggs to keep them safe. The students work with Professor Dale DeNardo at ASU’s DeNardo Lab, where they research how reptiles live and thrive in tough environments.
Stahlschmidt recently studied wild female water pythons in Australia. He was interested in finding out where they chose to lay their eggs and how long they attended them.
“Some stay for as few as three to five days, others are on the eggs for more than 50 days,” Stahlschmidt says.
Stahlschmidt found that two factors seem to influence a mother python’s decision to stay with or leave her eggs – the temperature and humidity of the nest. But exactly how these factors are related remains a mystery. In a previous study on water pythons, mothers tended to leave their eggs earlier if they laid their eggs in a nest with a warm, stable temperature. However, the pythons Stahlschmidt studied in Australia seemed to do the opposite.
“We’re still trying to figure out why that could be because it’s not as intuitive and adaptive as you would think,” Stahlschmidt says. “At ASU we have colonies of captive pythons, and the research I’ve done with them shows they use humidity and temperature cues from their environment to enhance their eggs’ water balance and temperature. To have a different response out in the field is interesting.”
There are other parental care behaviors wild and captive pythons do have in common. Brooding female pythons coil tightly around their eggs to help maintain water balance within the nest. But once eggs are enclosed in this tight space, the embryos have a hard time respiring, or getting oxygen from the nest environment.
“Coiling on the eggs is sometimes essential for embryo survival, but it comes at a cost,” Stahlschmidt says. “Since the embryos are developing in this low-oxygen environment, they become smaller, slower and weaker.”
What is a parent to do if providing one essential element of care means giving up another? Luckily, female pythons have found a way to balance the needs of their developing offspring. In another study, Stahlschmidt found that mothers will sometimes open their coils to allow for the exchange of gases.
This example of parental can be seen in other animals as well. Like pythons, mother birds must prioritize the needs of their eggs.
“Hatchlings need mom for protection and to keep them warm, but occasionally mom needs to leave the nest to get food, so she must balance a tradeoff between two important needs,” Stahlschmidt says. This is why birds often require both parents to care for eggs—one to attend the nest while the other forages for food.
Birds and pythons share something else in common as well. “They both evolved from reptile ancestors,” says Brashears.
The earliest sign of reptile evolution is dated at around 350 million years ago. Both mammals and dinosaurs eventually evolved from this diverse group, and birds later evolved from dinosaurs. Birds also developed a few important similarities to mammals. For example, both mammals and birds are endothermic, meaning they produce their own heat. According to Brashears, “99.9 percent of all animals in the world, including reptiles, are ectothermic. That means they get some heat and energy from food, but mainly from outside sources like sunlight.”
Why are so few animals endothermic? “It’s extremely expensive,” Brashears says. While humans need about 1,800 to 3,000 calories per day, a reptile of similar size might only need 300 to 400 calories per day.
Burmese pythons, however, are different from other reptiles. Although they need few calories compared to mammals, they have the ability to produce heat internally.
“It’s curious because they’re only endothermic when they are taking care of their eggs,” Brashears says. When Burmese pythons are brooding, they coil around their eggs and start twitching. This generates enough heat to control the temperature of the eggs.
“That can go on for two months,” Brashears says. “They won’t take food or water, they’ll just brood, and they lose a lot of weight.”
It makes sense that of all the reptiles, Burmese pythons would be able to produce their own heat because of how large they are. They can grow up to 20 feet long and their bodies also retain heat better. Brashears’ research is focused on finding the hormones related to python endothermy to better understand why endothermy first evolved.
“In some ways, pythons are an example of what we think birds and mammals might have been like,” Brashears says.
This makes them perfect for the study of endothermy. Why did such a small number of animals develop a trait that takes so much energy, and why are Burmese only endothermic when brooding? Brashears says that since Burmese pythons are only endothermic when caring for their eggs, it is possible that the body heat we enjoy today first evolved as a tool for parental care.