Seasonal variation in the behaviour of a short-lived rodent

Jana A Eccard,Antje Herde

doi:10.1186/1472-6785-13-43

Abstract

BackgroundShort lived, iteroparous animals in seasonal environments experience variable social and environmental conditions over their lifetime. Animals can be divided into those with a “young-of-the-year” life history (YY, reproducing and dying in the summer of birth) and an “overwinter” life history (OW, overwintering in a subadult state before reproducing next spring).We investigated how behavioural patterns across the population were affected by season and sex, and whether variation in behaviour reflects the variation in life history patterns of each season. Applications of pace-of-life (POL) theory would suggest that long-lived OW animals are shyer in order to increase survival, and YY are bolder in order to increase reproduction. Therefore, we expected that in winter and spring samples, when only OW can be sampled, the animals should be shyer than in summer and autumn, when both OW and YY animals can be sampled.We studied common vole (Microtus arvalis) populations, which express typical, intra-annual density fluctuation. We captured a total of 492 voles at different months over 3 years and examined boldness and activity level with two standardised behavioural experiments.ResultsBehavioural variables of the two tests were correlated with each other. Boldness, measured as short latencies in both tests, was extremely high in spring compared to other seasons. Activity level was highest in spring and summer, and higher in males than in females.ConclusionBeing bold in laboratory tests may translate into higher risk-taking in nature by being more mobile while seeking out partners or valuable territories. Possible explanations include asset-protection, with OW animals being rather old with low residual reproductive value in spring. Therefore, OW may take higher risks during this season. Offspring born in spring encounter a lower population density and may have higher reproductive value than offspring of later cohorts. A constant connection between life history and animal personality, as suggested by the POL theory, however, was not found. Nevertheless, correlations of traits suggest the existence of animal personalities. In conclusion, complex patterns of population dynamics, seasonal variation in life histories, and variability of behaviour due to asset-protection may cause complex seasonal behavioural dynamics in a population.

Highlights

Short lived, iteroparous animals in seasonal environments experience variable social and environmental conditions over their lifetime
A non-reproductive winter phase produces two distinct life history patterns: “young-of-the-year” (YY) animals, which breed in the breeding season of their birth, and “overwinter” (OW) animals, which are born late in the breeding season, live throughout the winter as subadults and mature late in their lives for the breeding season [12,13,14]
For OW animals, the life time spent in a premature, non-reproductive state differs among populations and varies with the length of the breeding season, i.e. with latitude or elevation [14,15,16] and total density [12]

Summary

Introduction

Iteroparous animals in seasonal environments experience variable social and environmental conditions over their lifetime. Animals can be divided into those with a “young-of-the-year” life history (YY, reproducing and dying in the summer of birth) and an “overwinter” life history (OW, overwintering in a subadult state before reproducing spring). Small mammals in seasonal environments experience typical annual population fluctuations [3,10] with low densities over winter, an increase phase in spring, a density peak in late summer, and a decline in autumn (Figure 1b). For OW animals, the life time spent in a premature, non-reproductive state differs among populations and varies with the length of the breeding season, i.e. with latitude or elevation [14,15,16] and total density [12]. OW and YY cohorts with different life history patterns co-exist during summer (Figure 1a)

Methods

Results

Discussion

Conclusion