Effects of Group Size on Behavior, Reproduction, and mRNA Expression in Brains of Brandt's Voles

For social animals, a moderate group size is greatly important to maintain their reproductive success. However, the underlying neurobiological mechanism of group size on behavior and reproduction has rarely been investigated. In this study, we examined the effects of group size (1, 2, 4 pairs of adult male and female voles raised per cage) on behavior and reproduction. Meanwhile, the mRNA expression of stress and reproduction response-related genes in male brains was detected. We found that Brandt's voles (Lasiopodomys brandtii) in the large-sized group fight more severely than those in the small-sized group. Meanwhile, male voles were more anxious than females. The average number of embryos and litters per female in the medium-sized group was significantly higher than that of large-sized group. In male voles, stress- or reproduction-response mRNA expressions were more related to final group size or final density due to death caused by fighting. Our results indicated that a moderate group size was beneficial to the reproductive output of Brandt's voles. Our study highlights the combined effects of stress- or reproduction-related gene expression or behavior in regulating the fitness of voles with different group sizes.

Automated summary

For social animals, maintaining a moderate group size is crucial for reproductive success. However, the neurobiological mechanism behind the effects of group size on behavior and reproduction has been poorly understood. This study investigated the impact of different group sizes on behavior and reproduction in Brandt's voles, as well as the mRNA expression of genes related to stress and reproduction in male brains. The results showed that larger groups led to more severe fighting among Brandt’s voles and increased anxiety in males. Additionally, the moderate-sized group exhibited significantly higher numbers of embryos and litters per female. The mRNA expressions related to stress and reproduction in male voles were influenced by the final group size or density due to fighting-induced deaths. These findings emphasize the importance of group size in regulating the fitness of voles through stress and reproduction-related genes and behaviors.