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.

Gut microbiota reflect the crowding stress of space shortage, physical and non-physical contact in Brandt's voles (Lasiopodomys brandtii).

Density-dependence plays a critical role in behavior and population regulation of small mammals, which is likely mediated by hormones and gut microbiota. High density-induced crowding effects often cause a combination of various social stresses including space shortage, physical contact and non-physical contact, but their distinct effects on gut microbiota in animals have not been investigated. In this study, we examined the crowding effects of space shortage and physical or non-physical contact stress on serum corticosterone and gut microbiota of Brandt's voles in both laboratory and field conditions. Our results demonstrated that the space shortage stress showed a more predominant impact on serum corticosterone and gut microbiota of voles than physical or non-physical contact stress; the crowding effects of non-physical contact stress became stronger in high density conditions, while physical contact stress was stronger in a larger group without density effects. High density or group size treatments under both laboratory and semi-natural enclosure conditions significantly increased the relative abundance of key differential taxa, including Bacteroidetes, TM7, S24_7, Streptococcus, and Lactobacillus; while high density or group size treatments decreased the relative abundance of Firmicutes, Staphylococcaceae, Bacteroides, Faecalibacterium, and Adlercreutzia. Our study suggests that high density-induced space shortage and physical contact or non-physical contact stress may play a significant role in behavior and population regulation through altering gut microbiota in small mammals. Our results may also have significant implications in rodent control or health management for livestock.

Timing outweighs magnitude of rainfall in shaping population dynamics of a small mammal species in steppe grassland.

Climate change-induced shifts in species phenology differ widely across trophic levels, which may lead to consumer-resource mismatches with cascading population and ecosystem consequences. Here, we examined the effects of different rainfall patterns (i.e., timing and amount) on the phenological asynchrony of population of a generalist herbivore and their food sources in semiarid steppe grassland in Inner Mongolia. We conducted a 10-y (2010 to 2019) rainfall manipulation experiment in 12 0.48-ha field enclosures and found that moderate rainfall increases during the early rather than late growing season advanced the timing of peak reproduction and drove marked increases in population size through increasing the biomass of preferred plant species. By contrast, greatly increased rainfall produced no further increases in vole population growth due to the potential negative effect of the flooding of burrows. The increases in vole population size were more coupled with increased reproduction of overwintered voles and increased body mass of young-of-year than with better survival. Our results provide experimental evidence for the fitness consequences of phenological mismatches at the population level and highlight the importance of rainfall timing on the population dynamics of small herbivores in the steppe grassland environment.