Genetic confirmation of a hybrid between two highly divergent cardinalid species

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Lately in my reading of science news articles, it seems like hybridization in new species as come up several times. I really appreciate the few videos and articles that Rob Carter has put out on the topic of hybridization. Helped me appreciate creation models even more.

But I wanted to share this paper because I thought it was beautiful in its simplicity. As far as I understand it, Jeanson’s model of speciation is created heterozygosity, migration, and isolation, versus a Darwinian model of mutation and natural selection.

With sentences in the paper like this, how can it be argued that created heterozygosity and isolation is not a superior model?

https://onlinelibrary.wiley.com/doi/10.1002/ece3.9152

The combination of evidence—visual, bioacoustic, and genetic—confirms that the parents of the described individual were a rose-breasted grosbeak Pheucticus ludovicianus (female parent) and a scarlet tanager Piranga olivacea (male parent). While these two species breed sympatrically across much of eastern North America, they exhibit somewhat different habitat preferences: scarlet tanagers typically prefer unfragmented, mature forest, while rose-breasted grosbeaks often will occupy second growth including forest with a relatively open canopy, although they will utilize adjacent edges or disturbed areas (Mowbray, 2020; Wyatt & Francis, 2020). The two species are phenotypically highly divergent and have likely not shared a common ancestor in >10 million years (Barker et al., 2015).

The genome of the hybrid was exceptionally heterozygous (Figures 3 and 4)—as is expected from an F1 hybrid with highly divergent parents—with a heterozygous base every 100–150 bp. This is also a likely underestimate. First, given that the parental genera were represented by RNA sequence data, the only regions we analyzed in depth here were coding regions, and these regions are constrained by stronger purifying selection than non-coding sequences (Ward & Kellis, 2012). Second, accurately calling heterozygous sites requires high coverage (Song et al., 2016); thus, we presume that many of the sites that differed between the parental genera but where the hybrid had one or the other genotype (i.e., was not heterozygous), might actually be heterozygous in the hybrid, but we lack the coverage depth to decisively call a heterozygous genotype. The fact that the sites where the hybrid had one or the other parental genotype occur in nearly equal frequencies (24 vs. 26 sites of 137) supports this interpretation.

In other news, how is everyone? I’ve been enjoying lots of science lately - had a science experiment birthday party for my oldest, my kids and I have been binging Mark Rober (anyone else a Mark Rober fan?). I’m reading Jennifer Raff’s book as recommended. My family has been enjoying many viruses I assume are recombined mutants to manage to survive covid isolation. Eye infections, ear infections a result. Many symptoms I’d forgotten existed in the world. :neutral_face::crazy_face:

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I’d start by noting that mutation and natural selection isn’t the right comparison, and you should be comparing Jeanson’s created heterozygosity and isolation with the mainstream evolved heterozygosity and isolation.

In the mainstream model, the ‘heterozygosity’ is a result of the isolation (leading to genetic divergence that gradually moves from fully compatible to fully incompatible). AFAIK Jeanson has no explanation for why there should be such a range leading to hybrids having different levels of heterozygosity.

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What in the paper do you think supports created heterozygosity? I don’t see anything relevant to that. Just the word “heterozygous” does not mean created heterozygosity.

Also, I hope you and your family feel better soon.

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Can you explain how you think those sentences support a created heterozygosity model?

Something like:
The created heterozygosity model proposes X, while evolutionary theory says Y.
This paper shows X (see quote).

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Very confused. The heterozygosity in that sentence results from the combination of two genomes that have been separate for 10 million years. That has nothing to do with “created heterozygosity”. Further, the standard model of speciation includes isolation followed by selection in differing environments, which you seem not to understand. This paper is not in any way support for Jeanson’s model. The paper may be beautiful in its simplicity, but you appear to have misunderstood it regardless.

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The heterozygosity here results from two individuals from highly diverged populations producing a hybrid offspring. How does that support speciation via a creation model where the heterozygosity is first created with two or more founding individuals, and then is sorta partitioned into different isolated populations over time?

That is basically the reverse of what happened here, where two different populations having been reproductively isolated from each other for something like 10 million years came together and produced an individual that was highly heterozygous because it got a mix alleles that were very different from each other from both of it’s parents. It’s not even clear that this new individual is capable of founding it’s own new species.

This paper supports only the idea that a highly heterozygous individual can physically exist, which wasn’t in dispute anyway.

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I’m trying to follow how you take this paper as support for Jeanson’s speciation model. Is the suggestion that If interbreeding between two isolated and relatively homozygous populations can result in an heterozygous individual, why should the process not be reversible, and heterozygous individuals result in isolated, homozygous populations?

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Yes, thanks for asking the question. I’ll just answer yours first and see what the response to this is, and then answer more above.

The creation model seems to be that the pair or seven who came off the ark would be extremely heterozygous, which is the case of this hybrid. It seems that the fact that these very diverged species can interbreed would support the creation model.

Otherwise I understand the the heterozygous nature of the hybrid is due to mutations since the populations diverged? Then why should interbreeding still occur?

(I’m actually still working through understanding the models. But writing down the original question as well as the responses help me think through everything. :slightly_smiling_face:)

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So the only relevance is that the paper shows that individuals from quite divergent species can produce offspring? Something which has already been known for years? And we don’t even know if this individual can reproduce or is sterile like many other hybrids? Ok.

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The fact that these very diverged species can interbreed merely shows that they came from a common ancestor. Since this is predicted by both universal common ancestry and the creation ‘kinds’ hypothesis, it doesn’t support one or the other.

Yes. The two species that interbred had a lot of genetic differences, and so the offspring was naturally very heterozygous.

Because none of the differences between the species affected their potential to reproduce with one another. This isn’t a difficulty for evolution at all, and I’m not sure how you got that impression. It’s just a somewhat unexpected and very interesting result.

I hope that answered your questions.

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Do we have any reasonably robust probability numbers on this, particularly for hybrids between different genera? I’d not be surprised that the probability might be low, but would be curious to find out how low.

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Probably not, as mutations don’t occur that quickly. Remember, selection and drift act much more on existing variation than on new variation.

You really don’t understand drift, do you?

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No, and I can’t imagine how we would ever come up with such numbers. But for the record, birds can often hybridize between genera. Happens frequently in ducks. I can easily find hybrids between Anser and Branta in local parks, for example. And the hybrids are generally not sterile, though they commonly have very low mating success.

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That wouldn’t be created heterozygosity, since (according to the creationist ‘model’) the individuals on the ark were born some 1600 years after creation. It might be selected heterozygosity, with the individual creatures being sent to the ark being chosen for maximal genetic difference yet still capable of interbreeding.

But any such heterozygosity would become mixed and muddled in the generations following release from the ark because all the individuals in one kind would be co-located and interbreeding (unlike initial creation, when different variants might be in different areas). It wouldn’t be retained.

No. The creation model would predict that all ‘kinds’ show similar levels of diversity[1] and all species can interbreed in this fashion, can since they’ve all been diverging for the same amount of time. It would also predict what that level of diversity was, based on fixation rates and population growth estimates.

But even if this did support the creation ‘model’, the ark scenario is untenable for so many reasons that need to be dealt with before this is even worth considering.

  1. Or possibly two levels of diversity due to some populations having a founding population of 2 and some having a founding population of 6 or 13.[2] ↩︎

  2. What exactly is the point of carefully selecting and preserving heterozygosity within the individuals on the ark if immediately after landing Noah is going to randomly wipe out 14% (or 7%) of those alleles? ↩︎

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Hybrid speciation does happen, and it has been known to happen in nature for some time. An interspecies hybrid in nature does not mean speciation will result. Ducks are notorious for making interspecies hybrids, and yet there are no new ducks. This form of speciation requires substantial hurdles, namely whether the hybrids are sterile or fertile (often they are sterile), AND the hybrids must be competitive with parental species who are already adapted to the local environment.
Meanwhile it is quite evident that allopatric speciation also happens, and all discussions on it imply that this is more common. Most species show no signs of having historically mixed genomes, so no recent hybrid speciation. All the considerable effort of drawing evolutionary trees between species hangs on there NOT being hybrid speciation very often, as that would confuse the branching order among related species. Finally, there are innumerable cases of gradually divergent populations that have not yet speciated, but are instead in the process of speciation in the traditional way. Of course, that too is no guarantee of speciation.
You are not going to re-populate the post-Noachian earth with 1.8 million species by hybrid speciation. Not without divine intervention and some frantic concealment of the evidence

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Where does the existing variation come from then?

I don’t see why it has to. Different kinds can have different biological programming which affects whether interbreeding can continue to occur after speciation. Also, I don’t see why there would be similar levels of diversity. I do think that there were kinds on the ark that speciated from created kinds - if there was a supercontinent, this was probably limited due to little geographic isolation. It would occur more with artificial selection since creation. I agree variation has been lost. I am also picturing an illustration from Rob Carter that shows 4 or so different ways drift would affect variation after the flood, but I wasn’t sure what search terms to use to find it.

The main reason I shared this example is because of the high heterozygosity in a hybrid of very diverged species that is in the same family, considered a rough estimate of a kind. (The paper gave half a dozen or so similar examples of highly diverged hybrids that I should look at more clearly).

The reply to this is mainly - So? We already knew that.

How many examples then are necessary then to make current model look weak?

Well, good, because no one is proposing that.

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Wait! Think this one through. You’ll get it. :slight_smile:

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Not sure, but certainly a minimum of 1, which you don’t have yet. Nor do you have a clear idea of what an example damaging to the evolutionary model would look like. What you have cited so far is exactly what would be expected.

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You’re missing the point, which is that hybridization doesn’t make the current model look weak. I’m not sure where you got this idea. It isn’t evidence against common ancestry, and it doesn’t support separate ancestry over common ancestry.

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From mutations that happened BEFORE the populations diverged, or, as you claim, God. You specified SINCE they diverged, remember?

An analogy for what you are doing here is sampling a single drop from a full bathtub, then claiming that the drop MUST have just come out of the faucet.

That’s the ratio of existing to new variation we’re talking about. It is correct whether the existing variation was created a few thousand years ago or over millions of years.

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