Inbreeding Depression and Genetic Diversity in Natural Populations

Inbreeding depression arises when mating between close relatives increases homozygosity, exposing deleterious recessive alleles and reducing individual fitness. In natural populations, the interplay between demographic history, mating patterns and genome‐wide variation shapes both the strength of inbreeding depression and the maintenance of genetic diversity. Small or isolated populations often suffer loss of allelic richness and elevated relatedness, which can undermine disease resistance, reproductive success and adaptive potential. Conversely, severe bottlenecks may purge highly deleterious variants, leading to complex, species‐specific outcomes. Understanding these dynamics is critical for conservation management, captive‐breeding programmes and the restoration of fragmented habitats worldwide.

Research from Nature Portfolio

Recent work on the northern elephant seal reveals that a profound near‐extinction event dramatically reduced effective population size to fewer than ten individuals. Whole-genome resequencing combined with veterinary and demographic data uncovered a strong genomic signature of an extreme bottleneck yet little detectable inbreeding depression for key traits such as body mass, blubber thickness and disease susceptibility. These findings imply that intense purging of deleterious alleles during the bottleneck may have eliminated much of the genetic load.

Studies of Antarctic fur seal pups on South Georgia have similarly found no consistent effects of individual or maternal inbreeding on birth mass, early survival or growth. Using both microsatellite and SNP array data, researchers show that inbred juveniles appear to be removed by selection between weaning and recruitment, highlighting a crucial, previously under-explored life-history window. Together, these marine mammal case studies illustrate how purging and life-stage–specific selection can modify or mask classical inbreeding depression.

Inbreeding Depression and Genetic Diversity in Natural Populations publication trend

The graph below shows the total number of articles in inbreeding depression and genetic diversity in natural populations across all publications each year (not limited to Nature Index journals).

Technical terms

Inbreeding depression: Reduction in mean fitness of progeny from related parents due to expression of deleterious recessive alleles.

Genetic diversity: Variation in alleles and genotypes within a population, underpinning adaptive potential and resilience.

Effective population size (Ne): The size of an idealised population that would experience the same rate of genetic drift.

Homozygosity: Presence of identical alleles at a locus, increased by inbreeding and demographic contraction.

Runs of homozygosity (ROH): Continuous homozygous segments in an individual’s genome, indicative of recent shared ancestry.

Lethal equivalents: A population genetic measure of inbreeding load, representing the number of deleterious alleles that would be lethal if made homozygous.

References

1. Genomic and fitness consequences of a near-extinction event in the northern elephant seal. Nature Ecology & Evolution (2024).
2. Detecting inbreeding depression in structured populations. Proceedings of the National Academy of Sciences of the United States of America (2024).
3. Little evidence of inbreeding depression for birth mass, survival and growth in Antarctic fur seal pups. Scientific Reports (2024).
4. Genomics advances the study of inbreeding depression in the wild. Evolutionary Applications (2016).
5. Nonequivalent lethal equivalents: Models and inbreeding metrics for unbiased estimation of inbreeding load. Evolutionary Applications (2018).