Data from: Intraspecific competition and inbreeding depression: increased competitive effort by inbred males is costly to outbred opponents

Theoretical considerations suggest that intraspecific competition is an important determinant of the severity of inbreeding depression. In support of this suggestion, previous empirical work shows that inbred individuals are weaker competitors than outbred ones, and that intraspecific competition therefore exacerbates inbreeding depression. Here, we report an experiment on the burying beetle Nicrophorus vespilloides, in which we recorded the outcome of competition between an inbred or outbred male resident caring for a brood and a size-matched inbred or outbred male intruder. We found that inbred males were more successful as intruders in taking over a carcass from a male resident, and were injured more frequently as residents or intruders. Furthermore, inbred males gained less mass during the breeding attempt, and had a shorter adult lifespan than outbred males. Finally, successful resident males reared a substantially smaller brood comprised of lighter larvae when the
intruder was inbred than when he was outbred. Our results have important implications for our understanding of the interaction between competition and inbreeding depression by showing that inbred males increase their competitive effort compared to outbred males, and that outbred opponents of inbred males suffer a fitness cost due to the increased competitiveness of the latter.