title: Causes and consequences of inbreeding in the banded mongoose
Creators: name: Wells, D
Publisher: name: Liverpool John Moores University
Year: 2021

description: Inbreeding and inbreeding depression have been studied since the days of Darwin and yet we are still making important discoveries today. These discoveries can inform conservation practices as inbreeding depression can contribute to population extinction. Inbreeding is also an important subject in evolutionary biology as the selection pressures arising from inbreeding depression can profoundly shape the evolution of breeding behaviour. Several recent theoretical studies have argued that inbreeding avoidance should not always evolve and that because inbreeding increases the proportion of genes shared amongst relatives it can influence the evolution of altruism. In fact, current theory is rather at odds with the almost ubiquitous observation of inbreeding avoidance in empirical studies. The banded mongoose (Mungos mungo) is a cooperative breeder which is unusual in that it frequently engages in incest. As part of the Banded Mongoose Research Project I have quantified the level of inbreeding and investigated both its causes and consequences. My study used 23 years of detailed behavioural observations on 1,956 individuals genotyped at 35-43 microsatellite loci. These genotypes were used to generate a nine-generation deep pedigree and inbreeding was estimated using the pedigree and microsatellite heterozygosity. Using generalised linear mixed models (GLMMs) I analysed the consequences of inbreeding using several measures of individual fitness and contributions to cooperative care. Finally I used piecewise structural equation modelling to investigate how changes in social variables influence individual breeding behaviour and ultimately cause inbreeding. I found that incest is common in the banded mongoose despite severe inbreeding depression in numerous traits. This can be detected using both pedigree and genetic measures of inbreeding but combining both measures can provide the most explanatory power (Chapter 2). Inbreeding depression in juvenile survival can be reduced by offspring care, but offspring care itself suffers inbreeding depression which should oppose the evolution of closed inbred systems (Chapter 3). Finally, I show that breeding behaviour is adaptively adjusted according to the risk of inbreeding as the social environment changes (Chapter 4). Understanding how inbreeding depression varies with genetic and environmental conditions is essential to explain the selection pressures that govern the evolution of mating behaviour. There is increasing awareness of the theoretical prediction that inbreeding depression does not inevitably lead to selection for inbreeding avoidance. In this thesis I find that inbreeding depression is not fixed but can be reduced by offspring care, which can potentially cause evolutionary feedback loops between inbreeding and care that have rarely been considered. Furthermore, inbreeding avoidance behaviour was not fixed but plastically adapted to environmental conditions which not only makes recording breeding behaviours more challenging but may also alter the selection pressures acting on them. In summary this thesis demonstrates the importance of several complexities of inbreeding behaviour in a wild population which must be more widely considered in order to fully understand the evolution of breeding behaviours.