title: Population sex-ratio affecting behavior and physiology of overwintering bank voles (Myodes glareolus).
abstract: Many boreal rodents are territorial during the breeding season but during winter become social and aggregate for more energy efficient thermoregulation. Communal winter nesting and social interactions are considered to play an important role for the winter survival of these species, yet the topic is relatively little explored. Females are suggested to be the initiators of winter aggregations and sometimes reported to survive better than males. This could be due to the higher social tolerance observed in overwintering females than males. Hormonal status could also affect winter behavior and survival. For instance, chronic stress can have a negative effect on survival, whereas high gonadal hormone levels, such as testosterone, often induce aggressive behavior. To test if the winter survival of females in a boreal rodent is better than that of males, and to assess the role of females in the winter aggregations, we generated bank vole (Myodes glareolus) populations of three different sex ratios (male-biased, female-biased and even density) under semi-natural conditions. We monitored survival, spatial behavior and hormonal status (stress and testosterone) during two winter months. We observed no significant differences in survival between the sexes or among populations with differing sex-ratios. The degree of movement area overlap was used as an indicator of social tolerance and potential communal nesting. Individuals in male biased populations showed a tendency to be solitary, whereas in female biased populations there was an indication of winter aggregation. Females living in male-biased populations had higher stress levels than the females from the other populations. The female-biased sex-ratio induced winter breeding and elevated testosterone levels in males. Thus, our results suggest that the sex-ratio of the overwintering population can lead to divergent overwintering strategies in bank voles.
authors.affiliation: Department of Biological and Environmental Science, Konnevesi Research Station, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland. Electronic address: saana.m.sipari@jyu.fi.
authors.forename: Saana
authors.initials: S
authors.lastname: Sipari
authors.affiliation: Department of Biological and Environmental Science, Konnevesi Research Station, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland.
authors.forename: Marko
authors.initials: M
authors.lastname: Haapakoski
authors.affiliation: Department of Biological and Environmental Science, Konnevesi Research Station, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland.
authors.forename: Ines
authors.initials: I
authors.lastname: Klemme
authors.affiliation: Unit of Physiology, Pathophysiology and Experimental Endocrinology, Department of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Rupert
authors.initials: R
authors.lastname: Palme
authors.affiliation: Lammi Biological Station, University of Helsinki, Pääjärventie 320, 16900 Lammi, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Sundell
authors.affiliation: Department of Biological and Environmental Science, Konnevesi Research Station, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Ylönen
mesh_terms: D000818:Animals; D003411:Arvicolinae / Q000502:physiology* / Q000523:psychology; D003345:Corticosterone / Q000032:analysis / Q000502:physiology; D005243:Feces / Q000737:chemistry; D005260:Female; D008297:Male; D012621:Seasons; D012744:Sex Ratio; D012726:Sexual Behavior, Animal / Q000502:physiology; D012919:Social Behavior; D013037:Spatial Behavior / Q000502:physiology; D013739:Testosterone / Q000032:analysis / Q000502:physiology
chemical_list: D013739:Testosterone; D003345:Corticosterone
keywords: Hormonal status; Overwintering; Population sex-ratio; Social interactions; Survival; Winter aggregation