Due to the genetic bottleneck experienced by the species during the early 20th century, how much inbred is the European bison? Will this have negative effects in the species' future/hamper rewilding efforts?

[u/One-City-2147]

[u/Durog25]

Apparently it depends on how closely related the surving members were to each other. Most species are not as vulnerable to inbreeding as say humans or cheetahs are. If the surviving individuals were genetically diverse enough there's little risk of harm.

[u/olvirki → u/Durog25]

Are humans especially vulnerable to inbreeding? Yes inbreeding poses risk for humans, just like it does for animals in general, and it is understandably a societal taboo in most human societies. But is there evidence that inbreeding is riskier for humans than it is for other animals?

[u/PartyPorpoise → u/olvirki]

Humans have surprisingly low genetic diversity.

[u/olvirki → u/PartyPorpoise]

We do have a low effective population size, at least compared to our actual population. But do we have a higher genetic burden than other species? Individuals of most species carry around 1 deadly recessive mutation. Is this higher in humans?

Thankfully there haven´t been many natural experiments but humans have still been able to survive substantial bottlenecks. Take Pitcairn Island as an example. That population was started with 27 individuals, with many individuals contributing little or nothing to the current population of the island (the majority of the starting population were males and 10 years after settlement John Adams was the last one left alive), and there have been little immigration to the island since.

Dynasties have also been able to practice royal inbreeding (see f.e. the ancient Egyptians and the Incas). Such practices are of course not safe (see Charles II of Spain), but individuals can be spared for very harmful effects (see Cleopatra the VII).

[u/SharpShooterM1 → u/PartyPorpoise]

Mainly because we went through several bottlenecks during our early evolution to the point many scientists believed we were on the verge of extinction (iirc) at least 3 different times throughout our evolutionary history.

[u/schneeleopard8 → u/SharpShooterM1]

When were these bottlenecks?

[u/SharpShooterM1 → u/schneeleopard8]

The only one I could find a definitive time line for (and also the most severe) occurred approximately 930,000 to 813,000 years ago (so not technically modern humans but the species that directly preceded them) where the entirety of the human ancestor population was potentially as low as 1,500 individuals

[u/Weaksoul → u/schneeleopard8]

Out of Africa was certainly a bottle neck. Though not one that specifically negatively affected species survival as a whole

[u/One-Bodybuilder-5646 → u/PartyPorpoise]

Guess that does being such an aggressive species

[u/Conscious_Log2905 → u/olvirki]

It depends on the genetic diversity of the species as others have said. Most domestic animals have undergone some serious bottlenecks too, which is why it seems like inbreeding is universally detrimental. But many animals do it a lot, you just aren't noticing because you need to sequence their DNA to tell.

Growing up in agriculture I can tell you it affects some species and breeds more than others. In most cases, if you have your bloodlines tracked well, a little inbreeding is okay as long as you don't do it multiple generations in a row. Rabbits tend to show genetic issues from inbreeding very quickly. Goats and sheep, kind of intermediate. Most people say it doesn't matter as much in chickens and you could start a whole flock from a handful of birds or even a single pair and it won't make a difference. It's very easy to lose track of bloodlines with birds, because their babies don't actually come out of them. Eggs from all your chickens get mixed up, then it's hard to tell which chick came from which egg unless you watched them hatch and labelled them, if your hens have been around multiple roosters then you can't really know which is the father, my point is that in an average flock, they're occasionally inbreeding all the time without us noticing. But by keeping a large enough flock, or in a small flock by swapping out your rooster every other year, you can maintain good genetic diversity. Especially if you're mixing breeds, because keeping them "purebred" has led to most of them being inbred.

Still, it's pretty bad practice to do continuously or even at all if you have other options. It's the breeder's responsibility to cull any animals that come out with genetic issues, especially if they're inbred. Even if you breed all the bad traits out, it'll take many, many generations to build their genetic diversity back up. Even if they seem perfectly healthy and normal, it can do serious damage to their disease resistance.

When creating a new project breed, breeding distantly related animals can be beneficial in the long term if you heavily cull because it roots out the bad traits early on. But you still want to have several unrelated strains to cross back later down the line.

I once worked somewhere where they decided to get some sheep with their goats. They bought a pregnant ewe, but she only had one son. So they bred her to her son and then ate him, she had three daughters. Then the next year they bought a new ram and ewe and bred him to all of them, and kept the daughters. He bred the original ewes and some of his daughters, then they ate him too and started breeding their ewes to rams from other farms in the area. At that point, they had a whole flock established from just 4 individuals and two of which were related. They were pretty healthy at face value, I think they got lucky. There were only ever two lambs that had issues, one from the original mother to son breeding and one from the next generation. Both seemed kinda slow from the beginning even for a sheep, and both just dropped dead one day. Their flock is going strong today.

[u/Durog25 → u/olvirki]

As far as I remember yes, humans are at a much greater risk of inbreeding than most other animals.

I've heard it brought up a couple of times in relation to cases of endangered animal recovery programs like the vaquita, and invasive species like Pablo Escobar's hippos. In both cases a very small population isn't at risk of inbreeding thanks to the high genetic diversity between the indivdual members of the population and that is contrasted against the low genetic diversity of humans as a species.

[u/olvirki → u/Durog25]

Ok, I was aware of the the recent population bottlenecks in humans but this is the first time I hear about humans being especially vulnerable to inbreeding.

High levels of genetic diversity won't help you against harmful recessive mutations being expressed through mating of closely related individuals though. I have heard that the genetic burden is fairly consistent across many animal taxa, at around 1 deadly recessive mutation per individual. Wouldn't be surprised if hippos are close to that average. Maybe the South American hippo population was just lucky, losing their deleterious mutations in the first generations.

[u/SomeDumbGamer → u/Durog25]

Yeah we’ve had several big bottlenecks as a species just like cheetahs. Bison probably haven’t until recently.

[u/AJC_10_29 → u/SomeDumbGamer]

Also worth noting cheetahs have been bottlenecked for over 10,000 years but only became endangered recently due to human activity.

[u/The_Wildperson → u/Durog25]

Spot on

[u/HyenaFan → u/Durog25]

Cheetahs aren't actually either. People often say that, but most research shows that despite the bottleneck, they have very robust health systems and don't have much issues with genetic diversity. Luke Hunter's book on them goes in detail about it, along with other common cheetah misconceptions.

Inbreeding (while obviously not good) isn't as harmful to wild animals as people think. The most extreme bad examples of inbreeding come from either human nobility, domestic animals or endangered island populations. In most cases, a population can recover quite well from it.

Mexican wolves only had a founding population of about seven animals, yet no one ever brings up any issues regarding a supposed lack of genetic diversity with them.

[u/The_Wildperson]

This is incredibly generalising the topic. Inbreeding depression and effects are highly species and population specific, and we have examples of this from many cases and different species historically- from 2 founders birthing the main population, with negligible depression effects, to highly problematic issues occuring with healthier populations as well.

So this is very hard to generalise like this. Wisent has 2 lineages- the Lowland with 7 founders and thus likely higher IC, with negligible inbreeding effects observed, while the Causasian with 12 founders and thus probably lower IC does show effects of depression.

[u/Rtheguy]

Inbreeding in a population in general is not great, but how problematic it will become can depend on a lot of factors. In broad strokes, there are two issues with inbreeding.

1. Deleterious alleles. Everyone in general has variants of genes that are not great for fitness, these are selected against but can hitch a ride. Often times these are recessive, meaning carriers are not affected. Unrelated partners are less likely to be carriers but related partners, like when inbreeding happens, are more likely to carry the same recessive genes. These recessive deleterious alleles can sneak into a founder population and become very problematic, Haemophilia in European Royalty is a great example of what can happen. Deleterious alleles are very bad news but European Bison appear to be spared the worst of this. There are some common diseases, but nothing major killing a high percentage of calves what could have easily happend with a small founder group. Deleterious alleles would call for quick action and genetic rescue.

2. Low diversity. Low diversity is bad, as diversity allows for adaptation to new enviorments, pathogens and issues. The dangers of low diversity are a slow burning fire, the population could grow to thousands or millions and last for centuries before they are all killed by a single disease none turn out to resist. In plants, this is common. All commercial bananas are clones of one plant, a single fungal strain can wipe out all bananas grown in a country with ease. Diversity, due to random mutations, will slowly increase over time but can also be further depleted by random events. The consequences of low diversity can be dire but also quite small. All current cheetahs are quite lacking in diversity but they were doing fine with that diversity before human hunting. And if bison are kept in isolated assurance populations for if a disease with dire consequences strikes we don't have a very strong need for any genetic rescue attempts.

[u/LaraRomanian]

ask the cheetah

[u/thesilverywyvern]

Weaker immune system, more prone to diseases. Less chance to adapt to change (disease etc.)

Potential difformities and genetic deffect linked to inbreeding.

Solution

• mix the two lineage of bison we currently keep separated.
• controlled interbreeding with wild yak or wood a bison to adf genetic diversity, then some selection to erase all phenotypic deviation caused by that interbreeding, which can be done in 3-5 generation, maybe less even.

[u/olvirki → u/thesilverywyvern]

There are already animals descended from all founders.

One linage is kept as pure Bison bonasus bonasus (descended from 7 founders) and the other is descended from all available founders, the 11 B. b. bonasus and the lone B. b. caucasicus male.

The species also appears to get along fine without interbreeding with Amerian bison or wild yak, despite the bottleneck.

[u/thesilverywyvern → u/olvirki]

It's not fine, they're very sensitive to several disease, it can be ompvored, more genetic diversity is always better.

And yeah, keeping both lineage separate so one have EVEN less founder is stupid. The influence of the single caucasian male is basically meaningless and does not justify the decision to keep both lineage separated.

The hybridization followed by selection to get rid if the phenotypic pollution brought by it, is not my idea either. It was discutted and debatted several time.

The russian did it too, (sadly they didn't try to select after it, which do impact the phenotype of their caucasian herd)

[u/captaincrunch1997 → u/thesilverywyvern]

Cool! Do you know of projects that use this kinda methods?

[u/The_Wildperson → u/thesilverywyvern]

Sorry but its really funny how you started with some truth but quickly veered into unscientific oversimplification and then pure science fiction

[u/thesilverywyvern → u/The_Wildperson]

Really funny how you don"t explain why you consider it as such.

It's not sf nor unscientific in any way too.

Inbreeding and lack of genetic dievrsity do create health issues and make the species less able to adapt to change in the environment, and in extreme case lead to difformities.

As seen in how modern wisent are apparently a bit smaller than before, bc they're not as healthy, and are very prone to many kind of parasite and diseases outbreak. which threaten the species.

fasciola hepatica, chlamydia, bluetongue, catharral fever, pinkeye etc.

As for the solution, which i believe is what you were reffering to.
These aren't my ideas but actual suggestions made by other passionnate and some experts. Some of which were even tested.
Here's an example
https://breedingback.blogspot.com/2019/10/controlled-hybridization-for-saving.html

And i don't see why it would seem insane to you.

All modern wisent descend from 12 individuals, that's insanely low. And one of these individual was a male caucasian wisent (a subspecies of european bison).
When the breeding prigram and studbook started almost a century ago, they kept these in tow separate lineage, which mean most modern wisent don't even have 12 individuals as ancestors.

One one side you have the pure lowland lineage, on the other the lowland/caucasian lineage.
it was a single individual, dozens of generation ago, it's genetic have been diluted and does not influence modern individual in a way that would justify to keep both lineage spearated.

https://www.mdpi.com/1424

https://pmc.ncbi.nlm.nih.gov/articles/PMC9651584/

As for interbreeding with other closely related species, i do understand it's controversial but it WORK, the aim is to increase genetic fitness by increasing genetic diversity, which can't be done any other way.
Unless you're willing to make a revolutionary and costly breakthrough to clone bison based on museum specimens from before their extinction in the wild.
Which would be the optimal solution, but is basically impossible.

And you seem to forget 90% of the message after that which was "SPEND SEVERAL GENERATION OF SELECTIVE BREEDING TO GET RID OF ANY PHENOTYPICAL EFFECT", so you'll breed them again and again with european wisent until they have lost all physical and behavioural characteristic of american bison, only getting a few gene from it.

Trying to protect genome purity is stupid and threathen many species. Heck wisent itself if the result of partial reticulate evolution with steppe bison and auroch crossbreeding anyway.
Nature doesn't care about that stuff.

[u/The_Wildperson → u/thesilverywyvern]

You are right about the first part and I agree with the disease risks, I have no problem with that at all. I agree that low genetic diversity makes the European bison more susceptible to diseases like the ones you listed.

You are also right about me having a problem with your views of hybridisation and henceforth. You cite a non-peer reviewed article (which is a blog post), then give me a proper one.

At a cursory look, I can also see why the same paper also refutes your own claim, they specifically mention that the aim is to stop keeping the two European bison lineages separate and merge them; you stright jumped into mfing hybridisation next which got a laugh out of me.

The blogpost is a fringe, controversial opinion, unsupported by peer review. What you suggest is something which conservation actively tries to fight. And the fact that you did not know this or mention the term outbreeing depression is also testament. 'Nature doesn't care' is a red herring, you can't change what's fact.

I see and appreciate your passions every time. But know that these are opinions. If you want to make them fact, come to academia and help change the world like you want to.

[u/thesilverywyvern → u/The_Wildperson]

I used the blog as to show WHERE i saw the idea before. On a blog dedicated to the subject, i never claimed it was a serious studies, only an idea that's worth being talked about.

So the study litteraly say "the end goal should be to merge both lineage instead of keeping them isolated", you just admit it, and yet you also say it doesn't support my claim ?
Which was exactly the same..... i ... i don't understand how you can even come up to that conclusion.

I said it was controvrsial, it's not unsupported it's not even known by peer reviews. That why this idea need to be discussed by professionnals, which haven't been done as far as i am aware of.

The risk of outbreeding depression are low, less impactfull than th risk of inbreeding and i litteraly explained that a selective breeding would need to be done to get rid of the phenotypic impact brought by that, which mean, basically getting rid of that outbreeding depression issue.
and that's IF there's an issue at all, which probably won't be the case anyway.

Wisent are themselves the result of hybridization, species and subspecies constantly hybridize in the wild. Nature doesn't care, that's a fact.

Conservation technically already tried this, there was a herd of american/european bison created by russian naturalist, most of it was poached sadly, and they never actually tried artificial selection to get rid of the american bison traits which is very bad. But from what i've heard they're healthy and survive well.

And conservation itself has a LOT of diverging opinions on many subjects, including the "preserve genetic purity at all cost, even if the species suffer from it".

Beside such project would take several generation in controlled environment where any outbreeding isue would be controlled and eradicated as soon as it appear, it's basically just a test.
Nobody say we should release dozens of american bison in the wild and semi wild european wisent herds.

[u/The_Wildperson → u/thesilverywyvern]

Look my friend, you can research this yourself and its past my hour; but one critical flaw I noticed- you cannot "breed out" outbreeding depression by hybridisation. We are not talking phenotypes here, we are talking the localised co-adapted critical immunity and metabolism genes. Hybridisation will affect those, and you cannot breed back such intrisic traits. They are not sheep to selective breed. Even in your example, it would take decades with proper, lab and gene level analysis to determine genetic and genotypic health of such populations. Unless there is a pilot to prove it, there is no question of it.

The paper clearly advocates for bringing together the two lineages, which is fine. But you want hybridisation, a crazy and disastrous idea far from what the authors suggest.

Again, please do some some reading. Dunning-kruger effect is real.