Day length and estradiol affect same-sex affiliative behavior in the female meadow vole

Abstract

Non-sexual social bonding between adult mammals remains poorly understood, despite its importance in many species. Female meadow voles are territorial and nest alone in long summer day lengths when circulating estradiol concentrations are high, but cohabit in groups in short winter photoperiods when estradiol secretion is low. The influence of day length and estradiol on same-sex huddling behavior was assessed in adult female pairs housed together in long day lengths (LDs) or short day lengths (SDs) from weaning. The behavior of intact, ovariectomized, and estradiol-treated ovariectomized females from each photoperiod was assessed during 3 hour partner preference tests. Intact SD voles, unlike intact LD voles, spent the majority of the test in proximity to their cage mates. Estradiol treatment of SD voles significantly reduced time spent huddling with the partner. Neither ovariectomy nor estradiol treatment significantly affected the amount of time LD females spent in contact with their partners. Low estradiol availability is therefore a necessary but not sufficient condition for maintenance of high levels of huddling. These results establish that ovarian hormones interact with photoperiod to affect same-sex social behavior.

Corticotropin-releasing factor receptor densities vary with photoperiod and sociality

“…3a), although some LD individuals huddled for extended periods of time (data shown are the subset of huddling data pertaining to subjects in this study, presented in Beery et al, 2008b). Across day lengths, individuals that huddled more than average (N40 min) had greater CRF 1 receptor binding in the caudal/dorsal portion of the lateral septum (t(7) = 4.56, p = 0.003, d = 3.06, Fig.…”

“…Tissue was collected and behavior was analyzed as reported in Beery et al (2008b), and described briefly below. SD voles used in this study were either ovary-intact and sham-operated (SDint), or ovariectomized at 6 weeks of age (SDovx).…”

“…Three-hour partner preference tests were performed on the study voles as previously described (Beery et al, 2008b) based on an established paradigm (Carter et al, 1995). Briefly, the focal vole was free to roam a three-chambered apparatus in which one familiar vole (partner) and one unfamiliar vole (stranger) were tethered in opposite chambers.…”

“…Social groups are initially composed of a female with her recent offspring, but mortality and immigration of both sexes occur such that by mid-winter, groups are no longer familial (Madison et al, 1984). Day-length cues are sufficient to mediate seasonal shifts in social behaviors in this species: female meadow voles housed in short, winter-like day lengths form partner preferences for a samesex cage-mate after one day of cohousing (Beery et al, 2009;Parker and Lee, 2003), whereas those housed in long, summer-like day lengths are significantly less social (Beery et al, 2008b;Ferkin and Seamon, 1987). This shift is most marked for females, as males are more socially tolerant than females, both in summer field conditions and in laboratory long days (Beery et al, 2009;Boonstra et al, 1993;Ferkin and Seamon, 1987).…”

“…Males were not studied, as they do not show day lengthdependent variation in huddling durations or partner preferences (Beery et al, 2009). Voles had previously undergone social behavior testing to assess the extent of social preference for a familiar same-sex partner over a novel individual (Beery et al, 2008b), as well as quantification of oxytocin receptor density (Beery and Zucker, 2010). CRF receptor densities were analyzed by day length, compared to oxytocin receptor density, and correlated with individual differences in social huddling behavior.…”