In fish, stressful parental experiences influence offspring behavior via epigenetic changes

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The research brief is a brief overview of interesting academic work.

The big idea

Parents exposed to predators pass information about at-risk environments to their offspring through changes in gene expression, but how this information affects the offspring differs depending on the gender of the parent. My colleagues and I have shown this using sticklebacks – a small species of freshwater fish that brightly colored males care about egg development – in a series of articles recently published in the Journal of Animal Ecology.

Sticklebacks fear a number of predators in the lakes and rivers they inhabit, including the freshwater sculpin, like the one seen here.
Jennifer hellman, CC BY-ND

First, we exposed mothers and fathers to predators. Next, we looked at their offspring and measured their behavior as well as how genes were expressed in their brains. We found that the sex of the parent exposed to predators is important, but surprisingly the sex of the offspring also changed the way information influenced behavior.

Fathers exposed to predators produced bolder sons who took more risks, but the father’s experiences had no effect on the daughters’ daring. Mothers exposed to predators, on the other hand, produced more anxious daughters and also more anxious sons. These sons and daughters had different gene expression patterns, corresponding to our behavioral results.

We also investigated whether these changes persisted into a second generation. In grandchildren, we again found complicated patterns of gender-specific inheritance.

So how does it work? It’s not that the experiences have changed the genes that parents pass on. Rather, what changes is the way these genes are expressed in the offspring. This variability in gene expression is called epigenetics.

Stickleback eggs showing embryos growing inside.
Through epigenetics, a parent can pass information to the next generation of sticklebacks like the ones that grow in these eggs.
Jennifer hellman, CC BY-ND

Why is this important

My lab is generally interested in how an animal’s experiences influence the development and behavior of its offspring. Biologists call it transgenerational plasticity, and it allows parents to give their offspring environmental information even before the offspring are born. For example, in mice, when fathers are trained to fear a particular smell, their offspring will be afraid of that smell even if they have not been trained to do so.

Researchers have found transgenerational effects in all kinds of species, including humans. In humans, grandparent experiences – such as food availability or smoking – can have strong gender-specific effects on weight gain in grandchildren.

But studying behavioral changes is much more difficult than studying weight gain, and our study, although in fish, is one of the most careful to date looking at gender and behavior in transgenerational plasticity. . Studies like ours could help researchers better understand how today’s stressful events might affect future generations. It could apply to anything from poverty or PTSD in humans to climate change in reef fish.

What is not yet known

Researchers still know very little about the mechanism of these gender-specific effects; How is it possible that fatherly experiences affect sons in one way and daughters in another? Plus, do these gender-specific effects have some kind of benefit for future generations? Researchers know that this mechanism also exists in humans, but whether these sex differences are harmful or beneficial remains a mystery.

And after

How parents raise their offspring also plays an important role in determining behavior. My colleagues and I want to better understand how the stress in parents’ lives can change the way they interact with their children. For example, if fathers are stressed and pass these effects through epigenetic changes to semen, do they also modify their fatherly behavior to amplify or minimize these epigenetic changes?

We are currently running these stickleback experiments and hope what we learn will be important for humans as well. After all, every human parent knows how stressful life can be.

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