I’ve been busy with Bill Laurance visiting the University of Adelaide over the last few days, and will be so over the next few as well (and Bill has promised us a guest post shortly), but I wanted to get a post in before the week got away on me.
I’ve come across what is probably the most succinct description of why inbreeding depression is an important aspect of extinctions in free-ranging species (see also previous posts here and here) by Mr. Conservation Genetics himself, Professor Richard Frankham.
Way back in the 1980s (oh, so long ago), Russ Lande produced a landmark paper in Science arguing that population demography was a far more important driver of extinctions than reduced genetic diversity per se. He stated:
“…demography may usually be of more immediate importance than population genetics in determining the minimum viable size of wild populations”
I paraphrase some of his main points below:
- Controversy broke out in the 1970 s when it was suggested that inbreeding was deleterious for captive wildlife, but Ralls and Ballou (1983) reported that 41/44 mammal populations had higher juvenile mortality among inbred than outbred individuals.
- Crnokrak and Roff (1999) established that inbreeding depression occurred in 90 % of the datasets they examined, and was similarly deleterious across major plant and animal taxa.
- They estimated that inbreeding depression in the wild has approximately seven times greater impact than in captivity.
- It is unrealistic to omit inbreeding depression from population viability analysis models.
- Lande’s contention was rejected when Spielman et al. (2004) found that genetic diversity in 170 threatened taxa was lower than in related non-threatened taxa
Lande might have been incorrect, but his contention spawned the entire modern discipline of conservation genetics. Dick sums up all this so much more eloquently than I’ve done here, so I encourage you to read his article.
Frankham, R. (2009). Inbreeding in the wild really does matter Heredity, 104 (2), 124-124 DOI: 10.1038/hdy.2009.155
Lande, R. (1988). Genetics and demography in biological conservation Science, 241 (4872), 1455-1460 DOI: 10.1126/science.3420403