Hybrid species vs species groups - which is the better solution

Curators
1

We are having some long and contentious discussions amongst the herp people regarding the best way to deal with taxa that are currently regarded as species that interbreed broadly at areas of contact. They are spread in the US and northern Mexico from east coast to west coast.

For example in the kingsnakes, there are currently 5 species which all interbreed broadly at areas of contact. Historically they were treated as subspecies of a single widespread species, but the latest published research has split them into 5 species. Many knowledgeable people disagree, but we follow the Reptile Database as our taxonomic authority and that’s what they use.

The problem lies in how to resolve the unidentifiable individuals at the zones of overlap.

One solution being put forward is to create a species complex that includes all five taxa, but that label obfuscates the information of which of the five taxa are actually interbreeding, and would make untangling that mess difficult if the taxonomy changes.

Would it be better to have hybrid taxa at each area of overlap, rather than one all-encompassing species concept?
What are the downsides to this arrangement?

So the complex contains species A, B, C, D, and E. Species A is on the east coast, and species E is on the west coast. Right now users are forced to choose one of these species, even though there is clear evidence they are hybrids/intergrades.

We can’t do traditional two-taxon species groups because many taxa would end up in more than one species group.

I am wondering if it would be better to have:

Species A

Species AxB

Species B

Species BxC

Species C

Species CxD

Species D

Species DxE

Species E

We would have to atlas each taxon hybrid at the area of overlap, but that shouldn’t be too difficult.

There are several groups of snakes, for example, for which this arrangement would resolve some angst until a better taxonomy is published and accepted.

Chris

2

В ботанике существует практика признания устойчивых гибридов на уровне вида.
Навскидку, например: Amelanchier × spicata, Narcissus × incomparabilis.

3

This is a tough situation.

I don’t think the species complex with all 5 species adds much value/would be worth it for the reasons you laid out.

The maximal hybrid taxa approach would work, though is also a pain.

I would offer two thoughts (and no answers):

  1. An additional consideration could be - what approach is easiest to roll back if these species “fall out of favor”? as I agree that the taxonomy is nowhere near universal acceptance.

  2. How common are the intergrades and can they reliably be diagnosed? If they are quite infrequent, an observation field might suffice.

4

It all comes of trying to segregate something that inherently resists separation. The concept of ‘species’ has yet to be formally defined; I would say that you just need to do what makes most sense.

6

The Curator Guide discourages the creation of hybrid taxa:
“Given their vague morphological delineation and taxonomic uncertainty, use of hybrid taxon concepts should be avoided whenever possible. Adding IDs of higher-level taxa is usually sufficient. In those rare cases when some external authority actually supports a named hybrid, we will tolerate it, but abide by the following guidelines…”
Personally, I think using a species complex is the best solution as it avoids the difficult task of delineating all the hybrids (which might be a waste of time anyway if the species are later merged). You would potentially loose some information, but you could also use an observation field to record the specific hybrids if wanted. Anyway, that’s just my 2 cents. I’m not a herp person, so take it with a grain of salt.

7

I have tried explaining this to you in the flag. I think you’re getting hang on the taxa ranks being used, and how complex taxa are used. Complexes can have an unlimited amount of children taxon. The Melanoplus montanus species complex has 32 species listed under it and can only be identified through examination of the male genital via dissection. The complex allows for identification before the species was split into this mass of taxa, but without shoehorning it into a species.

The same method is being applied to the kingsnakes. Before they were split, they were called the Common Kingsnake. The complex is literally being a stand-in taxon for L. getula sensu lato. Even if we followed your taxonomy, and treated the complex as one species, people are going to want to identify subspecies. What if there’s an individual you simply can’t tell what it is? You would place a species level id. That is exactly what the complex is accomplishing.

8

For oaks, we generally use literature and other published references to support hybrid combinations, it sounds like you have a bit of a broken “ring species” with just one side of the ring. If the hybrid zones and species are well delineated and documented in the literature, I’d second chawley’s recommendations for the “maximalist approach” of making all the species combinations.

If not well-supported or you have 3+ species hybridizing, you have to get more creative and either live with the subgenera/section-level classification (if either exists), or to use observation fields to create a dedicated space for laying out the hybrids (complex or otherwise).

Species complex groups may also be recommended in the case that there’s not general agreement in the literature and community on which hybrids exist and where and how to clearly delineate them. They’re also very useful to bin complex or unclear hybrids as well.

A dedicated group for manual addition of disputed/confusing/unclear hybrids can be very helpful as well.

I mainly focus on plants and have heard vague rumblings that herps are taxonomically “special” in some way, but haven’t seen any evidence of that so I think the oak hybrid thicket experience transfers well to what you describe.

9

I agree with your summary and think it’s a good analogous situation. Just adding a note to clarify that I’m not really recommending the maximal approach per se, just noting that it could work. If there’s another solution that could work reasonably well, I’d probably prefer it to having all the hybrids, especially if they wouldn’t get much use.

My understanding of the situation is that there are a limited number of hybrid combos (essentially linear, like a broken ring), max two species combos (at least in nature), and that almost all observations will be pretty clearly assignable to either a species or hybrid combo based on location (e.g., this individual is either species B or B x C). So disagreements about any observation would mostly be between those taxa. Thinking that way, having the complex might be useful as observations for which there is disagreement would have a CID of the complex (essentially the old species sensu lato) instead of all the way back to genus.

Lastly, I very much agree that I also haven’t seen evidence that

though some people seem to treat them that way. As a herpetologist myself, I would argue that herpers are taxonomically special in that they take particular (and sometimes perverse) pleasure in arguing/disagreeing about taxonomy vehemently.

10

Ох, в ботанике тоже есть “особые” таксоны. Возьмём тот же самый Taraxacum officinale, который дробят на 200 с лишним таксонов. Или та же Alchemilla - с её апомиксисом, тут уже границы видов сложно очертить.

11

Why even consider them separate species?

12

I agree with the latter. If the community here determines that these taxa behave as subspecies instead of species, it’s always an option to deviate from the accepted taxonomic authority, and use the subspecies names instead. That seems like it would be the cleanest solution here.

13

Yeah, but then you could slip into subjectivity, though that’s probably already happened with most taxonomy. It really is just subjective.

14

Except it has been split, and switching to this option would require a massive series of swaps affecting thousands of observations. The complex taxon representing the sensu lato is the cleanest solution because it avoids swapping the taxa again back to subspecies, and fulfills the placement of what the species used to be.

15

That and researchers and botanical authorities have concluded they’re separate species, I think people need to be reminded that it’s not really iNat’s lane to “leapfrog” the literature unless there’s compelling new evidence, and even then philosophically speaking, it’s not really our place to reject established taxonomy for personal reasons of expediency and/or more familiar species concepts.

16

I know inter breeding is not the sole criteria of species delineation. But if populations consistently interbreed with each other and are otherwise quite similar, then what is the basis for making them separate species? To put it another, what analytical utility is gained by considering them distinct species and not just slightly different subpopulations?

17

I’m not sure I understand your question. Oaks have species by morphology and genetics, but also happen to blur our clear little “species” boxes through extensive interbreeding while maintaining distinct genetic signatures.

They’re just a somewhat extreme/special case that pretty much is the final nail in the coffin for the “biological/reproductive species concept” in their ability to maintain separate species dictated by environmental selection while still forming a syngameon with oaks in their section in the same region.

A couple resources on the oak syngameon and the syngameon concept generally:

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/nph.16091

https://en.wikipedia.org/wiki/Syngameon

18

Why not both the hybrids and a complex for disagreements between species/hybrid combinations?