If you have a low population of an endangered species, how do you get the numbers up without inbreeding or ‘diluting’ the original species?



I’m talking the likely less than 50 individuals critically endangered, I’d imagine in 50-100 groups there’s possibly enough separate family groups to avoid inter-breeding, it’s just a matter of keeping them safe and healthy.

Would breeding with another member of the same family group* potentially end up changing the original species further down the line, or would that not matter as you got more members of the original able to breed with each other? (So you’d have an offspring of original parents, mate with a hybrid offspring, their offspring being closer to original than doner?)

I thought of this again last night seeing the Sumatran rhino, which is pretty distinct from the other rhinos.

Edit: realised I may have worded a part wrongly. *genus is what I meant not biologically related family group. Like a Bengal Tiger with a Siberian Tiger. Genetically very similar but still distinct.

In: Biology

Usually they just go with inbreeding. The Chatham Island Black Robins alive today all descend from one female.

A quote about the topic: [The study examined 95 mammal species, 20 percent of which are endangered and 10 of which are on what the authors call “the tipping point” where they could be at the “point of no return.” That tipping point, according to the authors, is a species with a population below 5,000 individuals.](https://blogs.scientificamerican.com/extinction-countdown/australian-mathematicians-say-some-endangered-species-not-worth-saving/) This means that normally, it’s extremely hard to bring populations below 5,000 back to safe numbers.

If the breeding pool is as low as fifty, it’s nearly impossible to raise it back up. A certain percentage of the animals will be infertile or die before adulthood. Then, you have to consider why the population has gotten so low. If the species is going extinct because of habitat loss, that will still limit the amount of animals that can survive.

In regard to your second question, evolution is constant. In this case, genetic drift is possible. This means that depending on the characteristics of the survivors, future generations may be different. Say you had 100 butterflies; 20% red, blue, green, yellow, and purple. Fifty randomly died, leaving 50% red, 30% blue, 28% green, 2% yellow, and 0% purple. About half of their kids will be red, and none will be purple. The species will have “accidentally” evolved to not have purple anymore. If this doesn’t happen, evolution will still happen, but it’ll take longer to notice.

You don’t. you don’t have much choice but inbreeding, hoping there’s no genetic abnormalities that’s going to amplify, and then hoping there’s never a disease that exploits their genetic similarities.

Inbreeding itself is not going to cause much if a threat. If conditions are right, you can get a population back up from literally a single breeding pair.

There are two issues with it:

– Genetic defects: this is less of an issue than one would expect, since any frequently occuring and serious defect will be removed from the gene pool rather quickly. It might reduce the rate at which early generations can breed.

– Smaller genepool -> less variety -> if conditions change, there is less variety to choose “successfull” variants from. This means the species will not be as good in adapting to changes for a certain time. This also means that diseases are more likely to wipe out a species, since less variety -> lower probability of resistant variants.

Neither of those things will make a species go extinct on its own. However, with the usual pressure and competition going on in nature it might be just enough to tip the balance against a species – particularly now, with environmental destruction forcing species to quickly adapt or die out.

You also have to take into consideration that not all species are equally prone to dangers that come with inbreeding.

Breeding doesn’t cause issues in 100% of the offspring. If even two offspring do not have significant issues, they can continue to breed. Eventually, they become genetically diverse again as the differences start to add up and there’s significantly less risk of genetic defects.

There was a story on 60 Minutes (US) about the organized lengths that affiliated zoos from all over the world use to reduce inbreeding while growing small animal populations. They keep track of the most genetically diverse animals and only mate those while avoiding genetically close pairs.

There’s the rule (of thumb) of 500, and the rule of 5,000. Generally speaking, a population with 5,000 members can breed back up to sustainable numbers with out any significant issues. With 500, it can breed to sustainable numbers, but there will be significant genetic difference from the original population. Which can be the inbreeding issues you mentioned.

But it’s still better for the health of a species to exist with inbreeding issues than to not exist at all.

You don’t. Genetic bottlenecking means that even when the numbers of a highly endangered species recover, it’s at the cost of genetic problems. IIRC the African Cheetah is a prime example of this.

Generally, the minimum amount of the species needed to avoid inbreeding is around 50, though zoologists would recommend at least 150

Is it possible to extract what you need (sperm/egg) from existing specimen before it gets to the final 50? Then fertilize an egg in a lab, implant it into a living specimen to have a birthed young without the risk inbreeding?

This is called a Genetic Bottleneck and it happens. Supposedly humans were reduced to only 3-10k individuals some 50k years ago.

>I’m talking the likely less than 50 individuals critically endangered, I’d imagine in 50-100 groups there’s possibly enough separate family groups to avoid inter-breeding, it’s just a matter of keeping them safe and healthy.

It doesn’t work like that.
There is no minimum number.

If you are lucky and you got only two specimens, niehter of which have dangerous recessive traits – then you can breed them up to high populations. Ofc. said population will contain extremely similar specimens which comes with its own “quirks”:

* Pros: due to extreme similarity, you can organ transpalnt between specimens
* Cons: due to extreme similarity, diseases will affect them the same way. Thus diseases will create much larger dips in the populaton before they evolve to coexist with the species. (Yes, parasites need hosts, so over time they evolve to be less deadly)

Ofc. if you get unlucky, you can have a last pair of organisms, that cannot produce viable offspring.

At the end of the day careful human selection – in terms of which individuals you allow to breed – can do wonders, when it comes to helping small populations to recover.



>Would breeding with another member of the same family group potentially end up changing the original species further down the line, or would that not matter as you got more members of the original able to breed with each other?

Good questions if that matters.

There are plenty of conservationist with the “genetic purist” borderline nazi-esque mentality.
Take the eurasian wildcat – which interbreeds with the common housecat.
So much so that in some places over 25% of the wildcat genetic material is from housecats. However that doesn’t lead to significant changes in the wildcat population in behavior or looks.

So “who cares?” can also be seen as a walid answer to the “is it an issue?” problem.

I was just listening to the Meateater podcast from 2016 and they were talking about North American Caribou. At the time they had 12. It’s up to 40 now with no genetic drift. So thats good news.

I’m not sure if this is the reason you brought it up, or if it’s just good timing, but there was a similar issue with the black-footed ferret population that was solved with cloning. Yeah, you heard me right, *cloning!*

The black-footed ferret population has been increasing, but every current living black ferret today can trace its ancestry back to about seven ferrets. So what did researchers do? They took frozen eggs from a ferret that existed in the 1500s and cloned a new ferret! Hopefully this new ferret will bring enough genetic diversity that it will ensure the species has no inbreeding problems in the future.

Today it was announced that scientists were able to clone successfully an endangered ferret whose genetic material was preserved from over 30 years ago. This will offer some genetic diversity into the endangered population.

Another method is through crispr Gene manipulation. Although this is quite controversial, and costly. I can only see this being used as a last resort.

They inbreed.

Despite its negative connotation, the notion that inbreeding always results in negative offspring is wildly out of control.

For those that do not know, when 2 people mate, each of them share half of their genes, to create a person.

46 chromosomes in each human means we share 23 each.

Let’s say 1 of those 46 chromosomes in dad are a precursor to down syndrome.

The parents mix their DNA and dad never shares that 1. The child is safe.

But what if dad mates with his sister, who ALSO has that 1 precursor to DS? Well now there’s a chance that both of them could pass it on.

The chances have doubled for that offspring to have DS. However, maybe neither of them pass it on, and everything is ok.

That’s the risk you take with inbreeding.

(This is grossly simplified)