New research suggests that stress exposure across generations may be more important than stress experienced within a lifetime.

The study, published in Hormones and Behavior, compared a population of lizards (Sceloporus undulatus) who had been living near fire ants for about 30 generations with a population that had been free of fire ants. Young offspring from both these populations were exposed to fire ants (an ecologically relevant stressor), the stress-relevant hormone corticosterone (at a dosage to mimic the elevation that occurs in response to a fire ant attack), or a handling control once a week for 43 weeks.

The researchers found that exposure to fire ants or corticosterone during early life did not affect the lizards’ stress physiology in adulthood. But the offspring of lizards from the fire ant-invaded populations did show a more robust stress response in adulthood compared to offspring from uninvaded populations, regardless of the early life stress they experienced.

PsyPost interviewed the study’s corresponding author, Gail L. McCormick of the Pennsylvania State University. Read her responses below:

PsyPost: Why were you interested in this topic?

McCormick: We live in a stressful world, and understanding how individuals respond to stress is becoming increasingly important for both human health and conservation management. When researchers think about how an organism responds to stress, we don’t always consider previous experience with stress. When we do, we usually think in terms of an individual’s experience within its lifetime, but less so the experience of its ancestors. These stress histories may both affect how animals cope with the increasing amount of stress imposed by environmental change. We investigated the relative influence of stress experienced by one’s ancestors (transgenerational) and stress experienced in one’s lifetime (during early life) on how that individual responds to stress as an adult (adult stress physiology).

What should the average person take away from your study?

Our work reveals that the stress experienced by an individual’s parents or ancestors may overshadow the stress that an individual faces within its lifetime. In this study, offspring of lizards from high-stress sites were more responsive to stress as adults, regardless of exposure to stress during their own lifetime. This change is likely adaptive, as increased stress responsiveness triggers survival-enhancing behaviors in this species (to escape from fire ant attack, a frequent stressor at high-stress sites). Early life stress, however, did not directly affect adult stress physiology.

Previous research demonstrates that early life stress can have long term effects on morphology, behavior, stress physiology, and immune function in a variety of species, including humans, but our work highlights the importance of also considering the effects transgenerational stress.

Are there any major caveats? What questions still need to be addressed?

The mechanism behind the transgenerational effect of stress exposure is still unknown. While long-term processes like natural selection could be playing a role, it is also possible that shorter-term mechanisms contribute as well, such as epigenetic effects (within lifetime effects that are transferred to offspring) and maternal effects (how mom provisions her offspring in utero or after birth/hatching).

Transgenerational and early life stress may affect other traits, such as behavior, growth, and immune function, differently, and, in lizards, it appears that they do. Preliminary results suggest that the combination of transgenerational and early life stress dictate that animal’s immune response to stress later as an adult.

Is there anything else you would like to add?

The relative influence of these stress histories on stress physiology may not be conserved from species to species. Nonetheless, our work suggests that transgenerational stress exposure may influence adult stress physiology and, in some cases, may be more influential than stress experienced by that individual. Both stress histories should be considered when investigating how an organism responds to stress.

The study, “Ancestry trumps experience: Transgenerational but not early life stress affects the adult physiological stress response“, was also co-authored by Travis R. Robbins, Sonia A. Cavigelli and Tracy Langkilde.