Inbreeding depression and a poor start in life

Abstract

Inbreeding is a widespread phenomenon that can decrease fitness. Inbreeding depression occurs because matings between relatives lead to an increase in homozygosity. Inbreeding is a pervasive force in evolutionary ecology driving the evolution of different traits, mating systems, and influencing population dynamics. It is generally assumed that the negative effects of inbreeding are exacerbated in stressful environments. In this thesis, I present seven experimental studies that explore whether life history, morphological, and sexual traits show inbreeding depression, and if this effect is increased by an interaction with an early stressful environment. Chapter 1 explores the preference for novel mates by males and females depending on the choosers’ previous sexual experience. I discuss the potential adaptive significance of these preferences and the likelihood of there being benefits of mating with multiple partners for both males and females. In the second chapter I look at the effects of mating with relatives on offspring fitness. I highlight the importance of considering the potential role of maternal effects when studying inbreeding depression, and the relative importance of genetic and maternal effects on reproductive traits and offspring performance. Chapter 3 addresses the interaction between inbreeding depression and an environmental stress, in the form of restricted food availability early in life. I test whether diet restriction during early development influences subsequent growth trajectories in ways that depend on the level of inbreeding. I then discuss potential hidden long-term costs that could affect reproductive success. In the fourth chapter I investigate the effects of limited food availability on sexually selected traits. I present a study testing whether a poor early diet is costly due to the reduced expression of sexually selected male characters. I aim to understand whether individuals are able to compensate for a poor start in life in various ways, or if they still incur costs that are evident after maturation. Chapter 5 investigates how differences in inbreeding and an early stressful environment influence the actual reproductive success of males. I argue about the extent to which inbreeding depression in males is due to natural or sexual selection. In Chapter 6 I explore how key factors act and interact to determine the strength of parental effects and whether these factors differ between mothers and fathers, and between their effects on sons and daughters. I discuss the multifaceted role of parental effects in a species lacking parental care. Finally, in the seventh chapter I provide a test of the effects of early life environment on the expression of genetic and maternal effects variance for a range of adult traits. I…