Hybrid Bison (and other well-known crosses) Reporting

I’m surprised that there are so few Bison X reported here. Does it matter that such a large % of Bison are not “genetically wild” (my casual term)? Shouldn’t we assume that they are crossed unless there is evidence to the contrary? Or, as one person wrote in a Forum discussion on wild vs. captive of bison, iNat doesn’t care about genetics. I’m also thinking about Celastrus (Bittersweet) genetic swamping.

Here are some related outside links:





Wild and semi wild bison in North America all look like pure bison. Most have some cattle ancestry but their ancestors back-crossed to bison many times. They average, what, 6% cattle genes? There’s no point in calling them hybrids. Really.

But they aren’t the same animal as full-blooded bison, either. How many genes are 6%? What do those genes do that would be different in a 100% bison? At what percent do we call it hybridization? 10%? 25%? 33.33333333%? In the arcane world of cladistics, what percent genetic difference causes a species to be split into cryptospecies?

I guess we need a Homo sapiens × neanderthal taxon to be created and all the current human records reassigned too then.


If this was a just behavior discussion I might agree with you - assuming the Cattle genes didn’t tend to domesticate their aggressiveness (which, I understand, it does). But this is a Species question in a Biology forum - plus we have relatively easy access to DNA information if the question matters. As the links above suggest - it matters. It matters to the future of the species - and what we call them in the scientific literature (and iNat research is part of that literature, not like other ID apps for entertainment and profit). It is a matter of responsible, honest, accuracy.

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At this point, genetic swamping makes that discussion moot. Also, I have only seen speculation that they were separate species.

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On the first point, is there a consensus that 6 percent gene retention makes something a hybrid and 2 percent does not?

European bisons were “save” by hybridization, but I wouldn’t call modern animals hybrids on iNat, same as humans have traces of hybridization, unless effect of cattle is visible on bison there’s not a big need of naming them so (it’s siilar to our situation with Herring and Caspian gulls, most Moscow Herrings are not pure birds, but far from all show visible signs of it and there’s no need to call them all hybrids).

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These “hybrid” bison are clearly not a new species. They breed back to the wild type bison just fine. There is no reason to set up a “hybrid” category for these animals that look just like non-hybrid bison.

Plants do this a LOT, animals less often but still more than one might think. The F1 hybrids are worth noting as hybrids, but after several generations of backcrossing to one of the parental types, the organisms essentially are the parental types but have brought in a few genes that may be helpful and certainly are harmless.

Note also that when the measurements of % species X in species Y are based on DNA sequences, they’re probably measuring mostly DNA that has no function, since when you add up the DNA that codes for proteins, regulatory sequences, necessary structures (e.g. where spindle fibers attach), telomeres, etc., they total a small part of the genome in most species. (Less than 10% in humans, for example.) Non-functional DNA is mostly old, dead viruses, proteins codes mistakenly written back into DNA without regulatory sequences, accidental duplications mutating away, unneeded genes that have mutated to nonsense, etc. Therefore, the genetic material from species X lingering in the species Y population may have no effect at all on the phenotype of species Y. Until such time as real phenotypic differences are observed, there’s no point in identifying these low percentage “hybrids” in most contexts (including iNaturalist) especially if they can breed to species X as well as 100% species X individuals do.


That does go to the taxonomists dilemmas - what is really a species and what isn’t? There has been a major re-ordering in birds but it has still not lumped Carolina and Black-capped Chickadees even though they interbreed in common areas as well as learn songs of the “other” species. I can see how remnant DNA exists in most species from the very earliest times but that doesn’t mean that recent (500 years or so) interbreeding is just moot - maybe with European Bison since, as you suggest, genetic swamping is complete, but not if we have pure-bred populations in North American Bison.

The human experience suggests that unless the inherited DNA from the other species is somehow detrimental to the survival or reproductive viability of individuals, it will be a very long time if ever before it disappears.

If what we accept as the modern human genome contains measurable amounts of genetic material from past hybridization events, I’m not clear why we would not apply the same elsewhere. I’m not talking about 1st generation beefalo but individuals whose cattle heritage is multiple generations ago


I disagree, but so it goes. (By the way, @cmcheatle is correct that harmless DNA sequences may take very long times to disappear, or may never disappear from the population that has some hybrid ancestors.)

The issue of the species concept isn’t really much of a dilemma, it’s just a category for the convenience of us humans, and to remain practical it should remain fairly consistent in application- and treating entities with a small percentage of hybrid genetic input that are backcrossed to the point that their phenotype is basically identical to that of non-hybrids (or fits within the range of phenotypes of that non-hybrid species) as simply belonging to that species is the convention.

This balance between coherence of a species group on both phenotypic and genetic fronts is essential to dealing with the reality that “pure” species that consist of a single coherent lineage lacking gene flow with congeners is perhaps most common in animals but does not appear to reflect the way “speciation” happens for most of life on earth. As sedgequeen hints, if we really start talking about plants the question becomes more or less irrelevant, giving way to others like “how do members of syngameons within the oaks remain distinct species in spite of ample gene flow and frequent hybridization?” https://www.biorxiv.org/content/10.1101/602573v2.full

Certainly if I go into a wet forest near a large body of water in my area most of the maples seen fall into a spectrum of hybrids and backcrosses between Red and Silver Maple. Many of these hybrids are clear in their intermediate phenotype (Freeman Maple), others leaning towards one parent or the other. But in adjacent upland areas where the population shifts clearly to Red Maple, some trees still show faint suggestions of some Silver input, subtle differences one doesn’t see in Red Maple populations more distant from silver maple populations. But these silver-influenced upland Red Maples are clearly not of the F1 Freeman phenotype, and obviously aren’t silver. They’re Red Maples, and they contain some (very recent) silver inputs even to the point of subtly affecting phenotype, but are presumably genetically mostly red maple, grow and produce buds and seeds of the type and in the same phenology as red maple- they’re Red Maple. A touch of genetic input from Silver Maple is a normal situation for Red Maple. This is a pretty normal situation in many groups of plants. Don’t even look at woody genera of the rose family. An expectation that a species is defined by a lack of recent genetic input from other species is not reflective of modern species concepts.


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