No evidence of inbreeding depression in fast declining herds of migratory caribou

Identifying inbreeding depression early in small and declining populations
is essential for management and conservation decisions. Correlations
between heterozygosity and fitness (HFCs) provide a way to identify
inbreeding depression without prior knowledge of kinship among
individuals. In Northern Quebec and Labrador, the size of two herds of
migratory caribou (Rivière‐George, RG and
Rivière‐aux‐Feuilles, RAF) has declined by one to two orders of
magnitude in the last three decades. This raises the question of a
possible increase in inbreeding depression originating from, and possibly
contributing to, the demographic decline in those populations. Here, we
tested for the association of genomic inbreeding indices (estimated with
22,073 SNPs) with body mass and survival in 400 caribou sampled
in RG and RAF herds between 1996 and
2016. We found no association of individual heterozygosity or inbreeding
coefficient with body mass or annual survival. Furthermore, those genomic
inbreeding indices remained stable over the period monitored. These
results suggest that the rapid and intense demographic decline of the
herds did not cause inbreeding depression in those populations. Although
we found no evidence for HFCs, if demographic decline continues,
however, it is possible that such inbreeding depression would be
triggered.