Estimates of Lethal Equivalents and the Cost of Inbreeding in Mammals

TLDR

Inbreeding costs in mammalian populations are poorly quantified, but reduced survival of inbred juveniles is a major known effect. The study estimates the inbreeding cost by regressing juvenile survival on inbreeding coefficient across 40 captive mammalian populations. Pedigree data from 40 captive populations of 38 species were used to perform the regression. Lethal equivalents ranged from –1.4 to 30.3 (mean 4.6, median 3.1), with no difference among founding types; a parent–offspring or full‑sibling mating increased juvenile mortality by 33%, likely an underestimate.

Abstract

Abstract: The costs of inbreeding in natural populations of mammals are unknown despite their theoretical importance in genetic and sociobiological models and practical applications in conservation biology. A major cost of inbreeding is the reduced survival of inbred young. We estimate this cost from the regression of juvenile survival on the inbreeding coefficient using pedigrees of 40 captive mammalian populations belonging to 38 species. The number of lethal equivalents ranged from –1.4 to 30.3, with a mean of 4.6 and a median of 3.1. There was no significant difference between populations founded with wild‐caught individuals, a mixture of wild‐caught and captive‐born individuals, and individuals of unknown origin. The average cost of a parent‐offspring or full sibling mating was 0.33, that is, mortality was 33% higher in offspring of such matings than in offspring of unrelated parents. This is likely to be an underestimate.