Stressing skinks during development has lasting consequences

Like humans, animals also experience stress, but instead of their stress being from an approaching deadline at work, it usually comes from the environment. For instance, the world is getting warmer and for animals – such as reptiles – whose body temperature depends upon the temperature of the world around them, getting too hot can stress them out. It gets even worse for these animals if they're still in the egg. Not only are they now experiencing hotter temperatures while still developing but these same temperatures could have stressed their parents before the eggs were laid, leading to the eggs getting a dose of the stress hormone corticosterone from their mothers. If the mothers pass this stress onto their offspring, then the eggs could be facing a double whammy. But can twice the stress have even more consequences than expected? To find out if incubating in a warmer temperature and having stressed out parents causes lifelong trouble for delicate skinks (Lampropholis delicata), Ondi Crino of Flinders University, Australia, teamed up with researchers from the Australian National University, Australia, the University of Wollongong, Australia, and the University of Brest, France.

In November 2021, the researchers painstakingly collected the tiny lizard eggs 1–3 days after they were laid, then incubated the eggs at either a cool (23°C) or a warm (28°C) temperature. They then injected the eggs with either a high or low dose of corticosterone, to mimic having stressed parents. Once the eggs hatched, Crino and the team measured how long the baby lizards were and how much they weighed. The lizards incubated at the warmer temperatures weighed less than those from the cooler temperature, and those from the eggs that got the higher dose of the hormone weighed less and weren't as long as other lizards. Surprisingly, having warm temperatures and higher stress hormones didn't make the lizards even smaller, suggesting that these different stresses don't team up, at least in baby lizards; but maybe they do later in life.

When the skinks had grown up a bit (105 days later), Crino and colleagues measured them again. The lizards from the warm incubator still weighed less than the ones from the cool incubator, but the lizards were now shorter as well, suggesting that the temperature they experience in the egg can have effects long after the lizards have hatched. The lizards given higher doses of the stress hormone still weighed less than lizards that weren't given an extra dose of hormone but were now the same length as the other skinks. Given these unexpected changes, the researchers waited until the skinks were 1.5 years old before measuring them a final time. As adults, the lizards from the warm incubator and the ones given the higher dose of the stress hormone grew less over the course of their lives, suggesting that the stresses they experience in the egg can last throughout their lives. But it wasn't just their growth that was different.

The team measured the levels of the stress hormone and how good the skinks’ mitochondria were at making energy. To their astonishment, Crino and colleagues found that the skinks given the lower dose of the stress hormone had higher levels of the hormone when they were adults. They also found that skinks incubated at the warmer temperature had less efficient mitochondria as adults. This means that a warmer world causes lizards to be less energy efficient. With the globe becoming increasingly hotter and animals experiencing more stress as a result, it's important to understand that having stressed parents can have lifelong consequences for their children.