Consistent scaling of inbreeding depression in space and time in a house sparrow metapopulation

Inbreeding often causes negative effects that, according to theory, may vary in severity with population size or harshness of the environment. Studying this in wild vertebrates has been prevented by the difficulty of collecting long-term data on multiple populations. We used genomic estimates of inbreeding to investigate its effects on fitness components and morphological traits in bird populations. Inbred individuals had lower survival and produced fewer offspring compared with noninbred individuals. Inbreeding depression was constant across populations with differing environments and population sizes. Consequently, populations with more resident inbreeding suffered higher total loss of fitness due to inbreeding. Our results highlight the importance of considering inbreeding in conservation and management of populations with a wide range of characteristics.