Lizard moms may prepare their babies for a stressful world

Stress changes the way animals allocate energy. During predator attacks or food shortages, hormones are released that help the body to access stored energy. But for pregnant females there's a potential trade-off. Stress hormones could rob precious energy from developing embryos, leading to offspring that aren't as healthy.

A research team led by Erik Wapstra of the University of Tasmania, Australia, tested the effects of stress on southern grass skinks, which, unlike many lizards, give birth to live young rather than laying eggs.

In the lab, the researchers recreated the physiology of a stressful situation by artificially raising levels of the stress hormone corticosterone in pregnant skins. Other skinks had their food intake limited, recreating the stress of a food shortage. The team then measured the health of the stressed mothers and their eventual offspring, and compared their state to mothers and offspring that weren't under stress.

The study found that stressed moms gave birth to smaller offspring that grew more slowly than those born to low-stress mothers. Stressed mothers themselves were found to be in better physical shape after giving birth than non-stressed mothers. That's a signal that when stressors are present, mothers tend to allocate energy to self-preservation first.

Despite seemingly getting the short end of the stick, the news wasn't all bad for offspring of stressed mothers. "We found that small offspring had larger fat reserves relative to body size…, which may enhance offspring survival in a stressful post-natal environment," the researchers write. Previous studies have also shown that smaller juvenile lizards often do better when predator density is high or when food availability is low.

It appears that a mother's stress-induced selfishness may actually help to pre-adapt her babies for a stressful world.