Deer mouse with offspring. Image credit: Chen et al. 2025 (CC BY 4.0)
Animals display an astounding variety of behaviors that they perform instinctively without needing prior experience. But how does the brain evolve to give rise to these behaviors? Two closely-related species of deer mice found in the United States display very different instinctive behaviors for mating and parental care. The individuals of one species mate with lots of different partners (referred to as promiscuous) and only the females care for the offspring. On the other hand, mice of the other species only have one mate at a time (monogamous) and share the parental care.
Previous studies have shown that a region of the brain called the preoptic area of the hypothalamus regulates mating, parental care and other instinctive behaviors. However, it remains unclear whether there are any differences in the brain cells of the monogamous and promiscuous deer mice that may account for the differences in their behavior. Chen et al. used an approach called single-nucleus RNA-sequencing to compare the cells in the preoptic area of the hypothalamus in these two species.
The experiments identified four types of cells that are present at different levels in the two species. For example, the monogamous deer mice had more cells that express a protein known as galanin, which is known to have a role in regulating parenting behavior in mice, frogs and fish. Furthermore, the cells of the monogamous deer mice, also had fewer “sex-biased” genes, that is, genes that are expressed at different levels in males and females, compared to the promiscuous species.
In both species, two types of cells that are able to sense sex hormones including estrogen and androgen were more abundant in males than females. These cells express many genes that are sex-biased indicating they may play roles in regulating male- or female-specific behaviors.
This work provides a large set of data for further investigations into how genes control behavior and evolve in deer mice and other animals. In the future, this may enable researchers to identify specific genes governing instinctive social behaviors, which may in turn lead to new diagnostic tools and treatments for neurodevelopmental diseases and neuropsychiatric disorders.
