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

A recent theoretical model suggests that intraspecific competition is an
important determinant of the severity of inbreeding depression. The reason
for this is that intraspecific competition is density dependent, leading
to a stronger negative effect on inbred individuals if they are weaker
competitors than outbred ones. In support of this prediction, previous
empirical work shows that inbred individuals are weaker competitors than
outbred ones and that intraspecific competition often exacerbates
inbreeding depression. Here, we report an experiment on the burying beetle
Nicrophorus vespilloides, in which we recorded the outcome of competition
over a small vertebrate carcass 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 either
residents or intruders. Furthermore, inbred males gained less mass during
the breeding attempt and had a shorter adult life span than outbred males.
Finally, successful resident males reared a substantially smaller brood
comprised of lighter larvae when the intruder was inbred than when it was
outbred. Our results shows that inbred males increased their competitive
effort, thus contradicting previous work suggesting that inbred males are
weaker competitors. Furthermore, our results shows that inbred intruders
impose a greater cost to resident males, suggesting that outbred
individuals can suffer fitness costs as a result of competition with
inbred ones.