Environmental modulation of same-sex affiliative behavior in female meadow voles (Microtus pennsylvanicus)

- We examined how winter conditions affect affiliation between female meadow voles.
- Females held under long or short days, 21 °C or 10 °C, food ad lib or restricted.
- Low temperature disrupted retention of social bonds in long, but not short, days.
- Winter-like conditions enhanced affiliative behavior between females.
- Preexisting social bonds did not preclude integration into new social groups.

The effects of temperature and food availability on social bonds and group formation are poorly understood. Because seasonal transitions in female social behavior facilitate the assembly of winter groups in meadow voles, we explored the role of same-sex female associations in winter sociality. To examine the effects of winter typical environmental conditions on same-sex female affiliative behavior, paired female meadow voles were housed in varying combinations of day length, temperature, and food availability for 7 weeks and then tested for social preference. In short days (SDs), lower ambient temperature increased huddling with unfamiliar females without interfering with existing social bonds, whereas lower temperature disrupted the retention of bonds in long days (LDs). Mild food restriction with no discernible effects on body mass enhanced affiliative behavior in SDs, but not LDs. A second experiment examined the effects of sex and day length on the propensity to aggregate with unfamiliar same-sex voles. Compared to LD females and SD males, SD females spent more time in group huddles with unfamiliar voles and displayed no social preference. These outcomes indicate that winter-like conditions enhance affiliative behavior between females and that pre-existing social bonds do not preclude integration into new winter social groups. The adaptive value of these behaviors is discussed.