Inbreeding: Module 6

Photograph by Christian Heeb / Redux (The New Yorker)

As we talked about in class, recessive deleterious alleles can become more frequent in populations with inbreeding, where fixing of alleles generally results in an increase in homozygosity within a population. In larger populations where inbreeding is less common, heterozygous individuals mask the function and consequences of deleterious recessive alleles. With inbreeding as a factor in a population however, the deleterious allele, originally recessive, is exposed due to homogenization and becomes more common in an the population; thus, variation is depleted through selection (Waller and Keller, 2020).

A example of this from the 1990s occurred in a population of Florida panthers (aka cougars, pumas, etc.). With a period of habitat destruction, the population of panthers weaned to about only 20-30 individuals. The resulting limited number of breeding pairs available led to excessive inbreeding within the population. Consequently, genetic variation in the population severly decreased while deleterious alleles expressing poor sperm quality, decreased fundicity, and increased cardiovascular disease became more common in the small population (Johsnon, 2010). Seeing the population near extinction, wildlife conservationists partnered with geneticists to complete a project of genetic restoration for the panthers to reduce inbreeding, restore genetic variation, and increase genetic diversity within the panthers. A handful of healthy panthers from a population in Texas were chosen to introduce gene flow in the Florida population.

In the following graphs from Johnson et al., the first (A) shows the population size of the panthers before and after the introduction of the Texas panthers to the Florida population (the introduction year is marked by the dotted line). As you can see, the resulting population size was significantly increased as fecundity and survivability greatly increased. The second graph shows the estimated number of heterozygous genes in the population over the same period of time. Before the Texas population was introduced, it is evident that most of the panthers were likely homozygous recesssive, but after the additional panthers were brought in, the heterozygosity in the poplation significantly grew (2010).

    

It should be noted that it was rather lucky that the chosen Texan population of panthers matched well with the Florida population because this method is not always beneficial. Populations that may be even more isolated than the panthers in this example can accumulate genetic differences that result in reduced fitness of the hybrid offspring (Neaves et al., 2015). Regardless, this new approach to wildlife conservation could prove useful in the next decades as conservationists fight agianst global changes to preserve dying populations like this one.


Johnson, Warren E et al. “Genetic restoration of the Florida panther.” Science (New York, N.Y.) vol. 329,5999 (2010): 1641-5. doi:10.1126/science.1192891

Neaves, L.E., Eales, J., Whitlock, R. et al. The fitness consequences of inbreeding in natural populations and their implications for species conservation – a systematic map. Environ Evid 4, 5 (2015). https://doi.org/10.1186/s13750-015-0031-x

Waller, Donald M., and Keller, Lukas F., "Inbreeding and Inbreeding Depression." Oxford Bibliographies, 26 Feb. 2020. DOI: 10.1093/OBO/9780199941728-0124

https://www.newyorker.com/tech/annals-of-technology/no-home-for-the-florida-panther