Stressed out lizard¹ moms tend to give their developing embryos² short shrift, but the hardship may ultimately be a good thing for the babies once they're born, according to a study published in the journal Physiological³ and Biochemical Zoology⁴. Stress changes the way animals allocate⁵（分配，指定） energy. During predator⁶ attacks or food shortages, hormones⁸ 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 lizards⁹, give birth to live young rather than laying eggs.

In the lab, the researchers recreated the physiology¹⁰ of a stressful situation by artificially raising levels of the stress hormone⁷ corticosterone（肾上腺酮） in pregnant skins. Other skinks had their food intake¹¹ limited, recreating the stress of a food shortage. The team then measured the health of the stressed mothers and their eventual¹² 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 juvenile¹³ lizards often do better when predator density¹⁴ 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.