How does inbreeding affect fitness and mate choice in natural populations?: insights from empirical studies on Drosophila melanogaster

[Truncated abstract] Genetic similarity between pairs of reproducing individuals may have a profound influence on fitness. The concept of inbreeding depression plays an important role in evolutionary thinking. Inbreeding theory has important implications for a variety of disciplines, including population genetics, behavioural ecology, evolutionary biology and conservation genetics. Despite its importance, there are still many basic questions surrounding inbreeding that remain unanswered. The four papers that comprise this thesis are empirical studies investigating inbreeding in the fruit fly, Drosophila melanogaster. This species represents an excellent model system for this topic because large pedigrees of individuals with known relatedness and inbreeding can be generated quickly in the laboratory, and previous work on this species means that molecular markers are readily available for genetic work. In the first study I empirically investigate the accuracy of inbreeding and relatedness estimates made from genetic data. In particular, I examine the effect of reduced genetic diversity resulting from differing demographic histories. I found that while reduced genetic diversity can significantly reduce the accuracy of estimates, they appear to be reasonably robust to some reduction in genetic diversity, retaining comparable accuracy to those made in an outbred population. These data provide confidence in the use of molecular estimates of relatedness for field studies of inbreeding and its avoidance in Drosophila melanogaster. The next two studies investigate the concept of optimal inbreeding for inclusive fitness benefits. Recent theoretical work on this topic predicts that in many cases, in order to maximise their inclusive fitness, individuals should choose to mate with close or intermediate relatives.