It has long been known that prolonged exposure to high levels of stress can be damaging to one's health and may even lead to a shortened lifespan. Furthermore, exposure to high levels of stress early in life can predispose the brain to be more sensitive to stress in the future, setting up a lifelong pattern of heightened stress responses.

Now, researchers show that early life stress harms not only the longevity of the individual who experiences it, but that of the individual's mate as well. Karen A. Spencer and colleagues at the University of Glasgow (UK) mimicked a high-stress childhood in zebra finches by giving them corticosterone (CORT), the stress response hormone, when they were nestlings (Proc. R. Soc. B doi:10.1098/rspb.2011.1291; published online 17 August 2011). They then paired both 'stressed' and 'non-stressed' birds with breeding partners of either the same or opposite treatment.

As predicted, birds who had received CORT as nestlings were more likely to have a shortened lifespan. Surprisingly, non-stressed birds paired with partners that had received CORT early in life were also far more likely to die within three years. Conversely, CORT-exposed birds' longevity was not enhanced by being paired with a non-stressed mate. Birds that both had experienced early life stress themselves and were paired with stress-exposed partners had an even higher likelihood of reduced lifespan than birds in all other conditions.

This study suggests that the shortened lifespan that results from stress in early life can be transmitted between partners. Pat Monaghan, first author of the study, tells Science News, “It's like giving them a disease.” The observed differences in longevity continued long after the birds were no longer housed with their breeding partners but rather in single-sex groups.

The authors suggest that this effect was caused by an inability of the CORT-exposed birds to participate in 'social buffering', a phenomenon in which the presence of a familiar partner reduces stress responsiveness by increasing levels of the bonding hormone. Social buffering is particularly important in zebra finches, which form strong pair bonds.

Interestingly, it has previously been shown that zebra finches exposed to stress early in life are discriminated against during the mating process. Breeding capacity and reproductive success were unaffected by early treatment with CORT. It therefore seems likely that this discrimination may have evolved as a means of preventing exposure to the increased risk of shortened lifespan that comes with a stress-exposed breeding partner.