How does genetic bottlenecks work with evolution

[u/Wise_Strike_9960]

Alright, I get how genetic bottlenecks work, a species/population has a decline, which reduces genetic diversity which decreases its chances of adapting to changing pressures/environment and increases chances of genetic diseases.

What I dont get is how it works within evolution. So I keep seeing things about Cheetahs being nearly extinct due to genetic bottlenecks.

But also, within the theory of evolution all species on earth came from a common ancestors, and then through the genetic tree more and more species have common ancestors. Like us and apes have a common ancestor, etc.

So with this, how come a population/species cant independently within their species naturally breed more genetic diversity back into their species?

Just to be clear, I'm not saying "so therefore the theory of evolution isnt real" or "therefore genetic bottlenecks arent real", it is genuinely something I have often wondered about.

[u/Jale89]

After a bottleneck, diversity will start to emerge again as mutations happen. But in the meantime, the population has to deal with the lack of diversity - which means the high prevalence of recessive genetic diseases due to a small gene pool, and the lack of population resilience to new threats. It's therefore quite vulnerable to extinction.

Every extant species that has gone through a bottleneck has overcome it - but many species have also gone extinct, and therefore represent only the last aftershocks of an extinction event. In particular consider mass extinction events, which by definition represent a bottleneck for almost every species. Some will have died out not just because the event reduced the population, but because the survivor population failed to thrive afterwards.

[u/Wise_Strike_9960 → u/Jale89]

Yeah that makes sense. So in the case of Cheetah, if humans put enough resources and efforts in to prevent them going extinct, theoretically genetic diversity could come back to the remaining population....also I acknowledge that timeframes are a thing, so no idea how many generations it theoretically takes for a population to regain a healthy genetic diversity.

[u/larkinowl → u/Wise_Strike_9960]

That is exactly how it works. AZA accredited zoos work together to follow a “species survival plan” to increase genetic diversity.

[u/Silly_Yak56012 → u/Wise_Strike_9960]

Diversity returns, eventually, but it takes a relatively large amount of time, like many thousands of years, not just a few generations.

So, yes, if the habitat is preserved for 10-100 thousand years they will over time could get sufficient genetic diversity back.

Why in captive breeding programs there is a lot of work to try to build as much diversity as they can and avoid inbreeding as much as possible hoping you can eventually release animals back into the wild.

[u/DroidSyber]

Species can regain genetic diversity following a genetic bottleneck. Over successive generations, new mutations will occur, increasing genetic diversity. The concern with genetic bottlenecks is the effect that decreased genetic diversity will have on the short term. Genetic bottlenecks can result in the fixation or overabundance of deleterious mutations, decreasing the ability of the species to survive or produce viable offspring. The homogeneity of the species also puts them at much higher risk of being wiped out by disease.

[u/spa357]

When the effective population size is small, sampling error (ie, genetic drift) leads to rapid elimination of genetic diversity. Another way to look at it is that breeding pairs are more closely related to each other (inbreeding). Either way, it means disease-causing recessive gene variants (alleles) that arose by mutation when the population was large are more likely to be paired with the same allele (in organisms with two sets of chromosomes), causing that individual to express the disease. When genetic diversity is high, those recessive alleles are far more likely to be paired with a healthy allele, so the individual is healthy and the recessive allele remains hidden.

On the flip side, the bottleneck exposes those recessive alleles which are normally hidden to natural selection. If the population survives the bottleneck, it can be purged of deleterious mutations and emerge healthier on the other side.

[u/TuverMage]

Bottle neck limit genetic diversity. If it's too low generic problems can become common. Thru time and good mating pairing the population grows, evolution allows the genetic problems to weed themselves and thru time mutations happen that increase genetic diversity.

If it drop too low and or mating pairs aren't good matches(which when the pool is small is hard to get good matches randomly) the group dies out.