Natural selection and avian personality in a fluctuating environment

Abstract

Individual animals differ in the way they cope with challenges in their environment, comparable with variation in human personalities. The proximate basis of variation in personality traits has received considerable attention, and one general finding is that personality traits have a substantial genetic basis. This poses the question how variation in personality is maintained in natural populations. The aim of this thesis was to study study the fitness consequences of animal personality in a natural population. This thesis addresses the consequences of individual personality at different stages of the life-history of the model species, the great tit Parus major, studying the relation between personality and dominance, dispersal, survival, reproduction, and offspring recruitment in the wild. A first step in studying how natural selection acts on personalities is the measurement of individual behaviour of wild individuals. Chapter 2 describes the method that we used to measure individual personality exploratory behaviour in a novel laboratory environment of great tits that were temporarily removed from the wild. We show that individual great tits differ consistently in their exploratory behaviour, and that the behaviour has a heritable component in the wild. In chapter 3 we study whether position in the dominance hierarchy measured on feeding tables in winter correlates with individual personality in the wild. We show that fast-exploring great tits have highest dominance ranks in territorial birds but lowest dominance ranks among non-territorial birds. In chapter 4 we assessed whether natal dispersal the movement between the place of birth and first reproduction is related to avian personality by measuring both the relation between natal dispersal distance and parental personality as well as differences in behaviour between immigrants and locally born juveniles. We show that fast-exploring parents have offspring that disperse furthest and that immigrants are faster explorers than locally born birds. The finding that fast-exploring birds have lowest dominance ranks in non-territorial birds suggests that they disperse further because they are outcompeted by others. In chapter 5 we describe how breeding performance (i.e. timing of breeding, clutch size, offspring condition, number of fledglings) correlates with male and female personality of the breeding pair. We show that reproductive success depends on the personality of both parents: pairs of fast-exploring birds (fast-fast) and pairs of slow-exploring birds (slow-slow) produce offspring of highest body mass at fledging. In chapter 6 we measure annual adult survival and number of recruiting offspring, to study how they relate to individual personality of male and female great tits. We show that selection fluctuates across years. Annual adult survival was related to exploratory behaviour but the effects were always opposite for males and females, and reversed between years. The number of offspring surviving to breeding also related to their parents personality, and again selection changed between years. The observed annual variation in selection pressures coincided with changes in environmental conditions (masting of beeches) that affects competitive regimes of the birds. We expect that the fluctuations in selection pressures play an important role in maintaining genetic variation in personalities.