Sib-mating enhances fitness in a haplodiploid beetle

Inbreeding is generally avoided in animals due to the risk of inbreeding depression following an increase in homozygous deleterious alleles and loss of heterozygosity. Species that regularly inbreed challenge our understanding of the fitness effects of these risks. We investigated fitness consequences of extended inbreeding in the haplodiploid date-stone beetle, Coccotrypes dactyliperda. We hypothesized that continuous inbreeding could result in reduced fitness, while outbreeding would either increase fitness due to heterosis or lower fitness if co-adapted gene complexes are disrupted. We established three breeding treatments with beetles from two geographically separated populations: Sib-mating (inbreeding), and outbreeding within- and between-populations. Between-population outbreeding groups of both populations had lower fecundity and collapsed before the experiment ended, while sib-mated and within-population breeding groups persisted for ten generations. Sib-mated females had highe...