Understanding what fitness benefits an individual gains by behaving in one way, rather than in another is the main aim of the field of Behavioural Ecology. In this study, my aims were to investigate the fitness consequences of variation in social mating system, and to elucidate how variation in parental care affects the fitness of parents and offspring. I used a combination of observational, molecular, experimental and meta-analytic approaches to attend to my aims. In particular, I investigated the relationship between mating systems and parental care in a wild population of dunnocks, Prunella modularis. Dunnocks are an ideal model system to study this interaction; the remarkable variation in social mating systems (monogamy to polygynandry) within my study population provided a natural experimental set-up to examine parental care behaviour.
In Chapter 2, after setting up a colour banded population of dunnocks in Dunedin, New Zealand, I examined the genetic and morphological differentiation between my study population and the thoroughly studied dunnocks from Cambridge, England. In Chapter 3, I investigated the plasticity of the mating system of dunnocks. Using data on the social mating system, genetic paternity, and relatedness, I tested predictions about variation in these characteristics as a consequence of the different ecological and demographic conditions experienced by dunnocks in my study compared to the Cambridge study. In Chapter 4, by using a meta-analytic approach, I tested the generality of the life history trade-off between parental effort and adult survival in birds. In Chapter 5, I used a field study conducted on my dunnock population, combined with a meta-analysis to test the hypothesis that the amount of paternal care to a brood is affected by the amount of paternity lost in that brood due to female infidelity. Finally, in Chapter 6, I coupled an experimental manipulation (within-brood food supplementation of nestlings) with the natural variation in mating systems of my dunnock population to assess nestling sex-specific vulnerability to rearing conditions and the fitness consequences of parental biased favouritism in care towards nestlings of different sexes.
This Behavioural Ecology research sheds new light on the importance of studying different populations of model organisms. Five conclusions about variation in population genetics, mating systems, and parental care can be made. (1) Multiple founder events are important in maintaining the genetic diversity of introduced populations. (2) Ecological and demographic factors, such as predation and density, are important elements in explaining mating system plasticity. (3) The amount of parental effort allocated to offspring has important sex-specific consequences on adult survival. (4) The paternity, or perception of paternity, of a male has little influence on the amount of paternal care allocated to offspring. (5) The type of mating system influences sex-specific nestling vulnerability, which consequently affects parental favouritism and the secondary sex ratio of broods.
