������Ƶ

Unpredictable light exposure disrupts biological sex differences in birds

Light helps us wake up, keeps us alert, and guides our sleep. But what happens when light becomes erratic? As a researcher studying molecular biology and animal stress responses, I've been fascinated by how environmental changes affect living organisms in subtle but powerful ways. In our in the Journal of Pineal Research, we discovered that irregular light exposure disrupts the natural molecular differences between male and female birds—especially in the brain.

We already know that light regulates biological rhythms in most animals. In chickens, for example, artificial lighting is commonly used to boost growth and reproduction. But beyond farming practices, I wanted to know how unpredictable light affects the brain—more specifically, the pineal gland, which plays a central role in regulating circadian rhythms through melatonin.

In collaboration with researchers at Uppsala University in Sweden and the University of São Paulo in Brazil, we exposed chickens to an unpredictable light schedule during early life. Then we examined their brains to assess changes in gene activity, microRNAs, and DNA methylation—chemical markers that regulate how genes are expressed.

What we found surprised us.

The differences between males and females in the pineal gland almost disappeared under chronic light stress. This loss was most evident in the epigenome—the layer of regulation that turns genes on or off without altering DNA. Interestingly, while the epigenetic differences faded, the gene activity still showed clear sex-specific patterns. This suggests the body may try to compensate when epigenetic regulation is disturbed.

One striking discovery was how much this disruption affected females. In control conditions, we saw robust molecular differences between sexes. Under stress, those differences vanished almost entirely in females, particularly in genes located on the Z chromosome—one of the sex chromosomes in birds.

As my colleague—and also author of the paper—Dr. Carlos Guerrero-Bosagna said, "This suggests female birds are particularly vulnerable to environmental stress at the molecular level. These findings raise questions not just about animal welfare, but also about how artificial lighting may affect biological rhythms in other species, including humans."

While our study focused on birds, the implications are broader. Today, many people experience erratic light exposure due to shift work, artificial lighting, or digital screens. If unpredictable light can erase fundamental molecular differences in birds, what might it be doing to us?

This story is part of , where researchers can report findings from their published research articles. for information about Science X Dialog and how to participate.