Next stop, the Hybrid Zone

[DitchingIt]

This pretty butterflyfish is a natural hybrid. It can be found around the Solomon Islands and eastern Papua New Guinea, living in a narrow contact zone between one species inhabiting the western Pacific and another in the south Pacific.

I felt really privileged to encounter both parent species, in the same zone, in one go: Chaetodon punctatofasciatus and Chaetodon pelewensis. But it seems that it wasn’t so odd after all, and a fascinating 1999 article explains why:

Firstly, both species pair bond, often for years on end, and together defend a territory. The authors found that 85% of adults seen in the hybrid zone were paired, so I was likely to have seen either species in a pair. (You can even see part of the tail of the hybrid’s mate disappearing in the bottom left of the the first photo.)

Secondly, the authors found areas in the contact zone with nearly 70% hybrid colouring, and apparently random colour mates. It was no surprise that I saw a mismatched pair.

Intriguingly, here is an example of species which have distinct colour pattern differences through most of their own ranges, yet don’t seem to rely on these to make mate choices.

The authors suggest that, " we demonstrated that color pattern evolution can occur prior to the evolution of assortative mating." Also that, “The behavioral, genetic, and phenotypic patterns between C. pelewensis and C. punctatofasciatus make it impossible to justify their continued species-level status under most current species definitions.”

Maybe you can share an observation of something similar, perhaps in another taxon, and maybe even explain what is going on in your example?

[AdamWargon]

Hybrids?! This is a Bat-Signal to botanists! Your post reminds me of Barbara’s comments about blackberries: This is a crazy-making situation for botanists.

@sedgequeen

The thing with members of the European Blackberry Complex is that they set seed apomicticly (without sex). Therefore, a population derived from seeds and covering a large area may be a single clone. It looks like a species because it’s growing alongside another clone that differs from it a little bit in several traits. That’s the kind of consistent, multitrait difference we’d like to treat as a species. And there’s a third clone. And a fourth. Etc. All a little different. Lots of “species.”

These all do have sex occasionally and produce seed from these unions. If the parents were different clones, these offspring are a little different from both – they are hybrids – and they can form a new clone that spread over a large area while retaining their traits, their differences from the other clones around. They seem to be behaving like distinct species.

As you can see, I’m not fond of treating all these different members of the European Blackberry complex as species. But there is a lot of variation in the group. Some of these variations help the clones adapt to different environmental conditions. Some differences look worth treating at the species level. But if you start dividing the group up, where do you stop splitting? This is a crazy-making situation for botanists.

[sedgequeen]

If I weren’t busy right now, I’d make a reply about the “Olympic Gull” a hybrid or backcross between Western and Glaucous-winged Gulls. I my area Oregon, they vary from very nearly as dark as Westerns (or are those just Westerns with a few G-w genes from past hybridization) to almost as pale as G-w Gulls. Olympic Gulls are the second most common big gull after Westerns. A mess.

[ljazz]

Just to clarify a bit situation with European blackberries:

Apomixis is not cloming, but creating new individuals whose genome is entarely sourced from one parent, but is recombined, so siblings are not the same (although mostly recognisable as such to experts - and I fully agree this should not be a species)

the biggest problem is that there are not two parents, but probably between 5-10 (caesia, ulmifolia, canescens, hirta, + a number of extinct parents that only survive in their hybrids). Further problem is that people partly domestivated some clones, introducing new morphological diversity.

But blackberries are not nearly as big of a problem as dandelions. The apomictic taxonomic insanity here is on levelel unmatched (there are stories you can find 50 species of dandelion on a single moderatly sized central-Euopean meadow).

[ljazz]

As a filthy botanist, I took me embarassingly long to see the parents were indeed different.

I caught myself thinking: is that not too close to be a separate species?, and then promptly remembered all the times I literally had to look at split hairs to ID a plant.

[silverydragon]

Me: are swallows and martins really different species? but they all look like swallows!

Also me: I’m sorry, your bright pink flower that is literally and genuinely identical to this other bright pink flower is in a different genus because the identical leaves are purely at the base and not on the stem.

On the subject of hybrids, I’m not even going to touch the nonsense that’s going on with Conostylis but I do offer up this observation of a hybrid Melaleuca that highly alarmed me the first time I came across it on the grounds that it would literally never have occurred to me that the parents are similar enough to confuse with each other, let alone produce offspring. I wouldn’t know how to explain it, but it seems to occur occasionally when the two species are in the same spot.

Not similar to the fish - that would be the Conostylis, but I’m scared of the Conostylis - but a hybrid nonetheless.

[sedgequeen]

@ljazz

Just to clarify a bit situation with European blackberries:

Apomixis is not cloming, but creating new individuals whose genome is entarely sourced from one parent, but is recombined, so siblings are not the same (although mostly recognisable as such to experts - and I fully agree this should not be a species)

The term apomixis is often used for cloning by seed (or even for cloning via bulblets, which I think it stretching it inappropriately). But does recombination as you describe occur in blackberries? I don’t know but am looking into it. (“Trust but verify” – a useful saying in science as in the military where it may have originated.)

[ljazz]

In apomixis, usually, some sort of recombination still occurs, and just the last step of meiosis is not completed. There are some forms, where it does not occur, but usually, when embryo arose from a somatic cell, we called it parthenogenesis, not apomixis (but then again I see some authorites lump parthenogenesis as a form of apomixis… so… :) If the subject is messy, why not the terminology).
But you are right, apomixis itself does not necessarily imply recombination.

(in Rubus, both occur (and often in the same individual, along with normal sexuality; third paragraph of https://academic.oup.com/aob/article/120/2/317/3578273) , as well as (allo)polyploidisation, so the mess is as big as plants can produce for a taxonomer; that same article states 750!! sp of Rubus sect Rubus in Europe!)