Does personality in small rodents vary depending on population density?

Abstract

Personality means an individual's unique way of behaving and reacting to the environment. It is a stable and heritable trait, which is expressed consistently in different situations. The aim of our study was to develop novel tests to depict the personality structure of the bank vole Myodes glareolus, and to determine if the phase of the population cycle, i.e. population density, affects personality. We focused on some central aspects of bank vole behaviour: mobility, risk taking, exploratory behaviour, dominance, and aggressive behaviour towards pups. These behaviours were chosen because they directly affect bank vole survival or fitness or are classified as important factors of personality in other species. In total, 192 males from different populations went through four behavioural tests, in which 20 variables were measured. The tests were repeated after 3 weeks, which verified that all traits were stable, i.e. repeatable between trials. Three personality compounds emerged, named extroversion, novelty seeking and infanticide. Extroversion included dominance and mobility, while novelty seeking consisted of risk taking and exploration. Infanticide encompassed all indices measuring harmful behaviour towards pups. Mobility and dominance were connected, possibly because both seem to depend on condition. Time spent in captivity increased extroversion, which may be explained by good food, stable conditions and acclimation to strong social cues. Novelty seeking was connected to repeatability which could mean that novelty avoiding individuals adjust their behaviour to match new environments. Population density affected the infanticide trait but not novelty seeking or extroversion.

Infanticide effects on behavior of the bank vole (Myodes glareolus) in the fragmented breeding habitat

“…Explanation for this is probably the infanticidal males' proneness to take more risks and direct movements also into the new unknown areas compared to noninfanticidal males moving more in the familiar environment. Korpela et al (2011) found relatively high correlation between male infanticide and novelty-seeking behavior in a personality study conducted in laboratory but using wild-caught voles. Dominant males are found to be more often infanticidal against unrelated pups in laboratory mice (Mus musculus) (Vom Saal and Howard 1982;Huck 1984), but the picture with free living voles is not so clear.…”

“…Thus, we do not expect any difference in female behavior due to the infanticide treatment, but habitat fragmentation may decrease female movement area size. Infanticidal males have shown to be more aggressive in laboratory (Vihervaara et al 2010) and shown more novelty-seeking behavior (Korpela et al 2011) which are expected to lead to higher activity also in the field.…”

How Do Infanticidal Male Bank Voles (Myodes glareolus) Find the Nest with Pups?

“…However, like shown before (Korpela et al 2011) infanticidal males were more active in moving around and seeking the vicinity of the boxes than the non-infanticidal ones. Korpela et al (2011) showed that the infanticidal males are more bold in personality traits than the non-infanticidal conspecifics (Korpela et al 2010) and in field studies infanticidal males are more active and move over larger distances than non-infanticidal ones (Haapakoski et al 2015).…”

“…Korpela et al (2011) showed that the infanticidal males are more bold in personality traits than the non-infanticidal conspecifics (Korpela et al 2010) and in field studies infanticidal males are more active and move over larger distances than non-infanticidal ones (Haapakoski et al 2015).…”

“…Population density is increasing with advancing breeding season, and thus it can be predicted that per capita gain for committing infanticide would be greater in low densities of early breeding season (Opperbeck et al 2012). However, there is an alternative view that numbers of potentially infanticidal individuals would be greater under high densities (Korpela et al 2010(Korpela et al , 2011, despite of intraspecific competition and social harassment, possibly affecting or hindering success of an infanticidal act. Studies monitoring proportions of infanticidal individuals along the population density gradient over breeding season are lacking.…”