Intergenerational effects of inbreeding in Nicrophorus vespilloides: offspring suffer fitness costs when either they or their parents are inbred

Inbreeding depression is the reduction in fitness caused by mating between
related individuals. Inbreeding is expected to cause a reduction in offspring
fitness when the offspring themselves are inbred, but outbred individuals
may also suffer a reduction in fitness when they depend on care from
inbred parents. At present, little is known about the significance of such
intergenerational effects of inbreeding. Here, we report two experiments on
the burying beetle Nicrophorus vespilloides, an insect with elaborate parental
care, in which we investigated inbreeding depression in offspring when
either the offspring themselves or their parents were inbred. We found
substantial inbreeding depression when offspring were inbred, including
reductions in hatching success of inbred eggs and survival of inbred offspring.
We also found substantial inbreeding depression when parents were
inbred, including reductions in hatching success of eggs produced by inbred
parents and survival of outbred offspring that received care from inbred parents.
Our results suggest that intergenerational effects of inbreeding can
have substantial fitness costs to offspring, and that future studies need to
incorporate such costs to obtain accurate estimates of inbreeding depression.