To be or not to (apart)?

New cichlid species and taxonomy
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Willem Heijns
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To be or not to (apart)?

Post by Willem Heijns » Sun Jun 16, 2013 6:56 am

It's a beautiful Sunday. Time to contemplate taxonomy and its rules. Here's a statement to get you through the day:

"Allopatric populations can never belong to the same species."

Any opinions?
Slàinte mhath!

Uilleam

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cichla
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Re: To be or not to (apart)?

Post by cichla » Sun Jun 16, 2013 8:41 am

Hi Willem, dear all,
first of all, good to know that it is a nice day in Holland (I am assuming that you are talking about the weather), because in 80% of the cases we get the very same weather conditions one or two days later in northern Germany. So, I expect a sunny Monday. ;-)
Willem Heijns wrote:"Allopatric populations can never belong to the same species."
Well, it depends on the species concept. If you treat a species as a tokogenetic assemble (in a strict sense) then – for sure – every single population separated by a physiogeographic barrier has to be treated as a different species. It is, because (at least usually) the specimens (individual members) of a particular population are more closely related to each other than to the members of any other population. In such cases it doesn't matter whether there are genertical/phenotypical differences or not.

This, however, wouldn't represents the kind of species what we are usually treat as a 'good species'. So, we may recognize species only if these are differentiated by phenotypical features. In a more modern (philosophical) sense it means that two population (even they are distinguishable by DNA/RNA or not) belong to the very same species when ever the members (specimens) are showing the same phenotypical appearance. Sometimes it is called the evolutionary coherence. Other natural natural philosopher call it the ''Property Cluster Kind''.

Anyway, the fact that a population are named as a species has to do also with the desire to name something. By the way it is the same reason why every montypic clade gets its own name.

Since the Code (international code for zoological nomenclature) call for diagnostic characters we should follow a more pragmatic species concept and name only such population which have an evolutionary fate.

Best, cichla (IS)

Willem, where do you found the phrase?

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Willem Heijns
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Re: To be or not to (apart)?

Post by Willem Heijns » Sun Jun 16, 2013 11:03 am

My dear friend Ingo, you surprise me. I found the phrase in a book you recommended to me (Do species exist? by Werner Kunz). He advocates the species concept being "a gene flow community".

So the statement could be reformulated as: "A species is defined by a continuous gene flow between its members". Any other species concept does not reflect reality in nature and is therefore artificial.

I hope some other members of the forum will also jump in here...... :?
Slàinte mhath!

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Re: To be or not to (apart)?

Post by Bas Pels » Sun Jun 16, 2013 2:59 pm

Put as broadly as Willem put is, I'd say 'no'

If we have a species, that is, a monophyletic group, it is possible one population can become separated, and might therefore evolve rather rapidly. The rest? Nothing chances, nothing happens, they are still the same.

As an example, the cichlids from the Nicaraguan kraterlakes are thought to be descended from Amphilophus citrinellus. Clearly they are not A citrinellus - but just as clearly, the resulting A citrinelluys, which are polyfyletic, are still A citrinellus. No reason to make new species

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Re: To be or not to (apart)?

Post by michi tobler » Sun Jun 16, 2013 3:33 pm

Hi all,
just to engage in superfluous fun. The notion that there is such a thing as a species, is just flawed. Species - by nature - are dynamic entities of evolution. The mostly come about gradually. Whether you recognize a species is dependent on the species concept you are applying, of which there are many. So, what a species is depends on the goggles you have on. It depends on your perspective, which may change depending on what scientific question you are asking. Very often (not always), taxonomy's biggest flaw is that it circumvents the scientific process, as it is not about hypothesis testing. If I want to prove that two populations are different species, I can surely collect some kind of data that shows that they are. Then I just apply the species concept that fits my data and supports my notion. How about people showing that new species are recognized so only if they fulfill the criteria of at least three (or ten) different species concepts with independent datasets? Species are hypotheses. We should test these hypotheses, not just succumb to our preconceived biases!
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Re: To be or not to (apart)?

Post by cichla » Mon Jun 17, 2013 5:04 am

Dear Willem, Bas, Michi; Dear all,
Willem Heijns wrote:I found the phrase in a book you recommended to me (Do species exist? by Werner Kunz)
LOL. Frankly, I didnt read it yet, but many of Kunz's papers.
Bas wrote:If we have a species, that is, a monophyletic group, it is possible one population can become separated, and might therefore evolve rather rapidly. The rest? Nothing chances, nothing happens, they are still the same.
I dont think that the question whether a group is ''monophyletic'' or not (in a cladistic sense) is connected with the statement cited by Willem. It is a different issue.
Michi wrote:Species - by nature - are dynamic entities of evolution. The mostly come about gradually. Whether you recognize a species is dependent on the species concept you are applying, of which there are many.
Yes, close to my own thoughts. Thanks.
Kunz wrote:''In the light of modern post-Darwinian biology, however, neither morphological, ethological, physiological, chromosomal, genomic or DNA sequence features nor any other intrinsic properties can any longer be regarded as essential to a species''
I agree 100%. But does it mean that every single allopatric population represents a different species in an evolutionary sense?

Species have – I think - an evolutionary essence. Not in a sense of the typological thinking but in a meaning of evolutionary coherence.

If we would follow the strict idea published by Kunz (earlier published by Avise & Ball 1990 - I think) than every single allopatric population needs to be named. In freshwater fish every single drainage is like an island (Rosenzweig: ''freshwaters are like fish archipelagos''). So, it seems better to keep it more practical. If there are no phenotypical differences then treat these as members of what we usually call a species. Otherwise we have to name ''things'' which will never like that what we usually calling a 'good species'.

Cheers, IS

By the way: how Willem calls for – I would like to read more opinions on this topic too.

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Re: To be or not to (apart)?

Post by Willem Heijns » Mon Jun 17, 2013 8:18 am

@ Michi,
I'm having trouble trying to follow your logic. About species you say:
1. The notion that there is such a thing as a species, is just flawed.
2. Species - by nature - are dynamic entities of evolution.
3. Species are hypotheses.
My main question to you is: do you believe species exist in reality? Or are they a human construct, created for convenience? In other words: what are your goggles? :shock: 8) :D
In addition: recognizing species (meaning: determining to which species an organism belongs?) is quite a different question from the one asking: what is a species? A species concept is about the latter. Having chosen a concept, assigning organisms to species is guided by that concept. Have you as yet formulated and tested a hypothesis about species? I would be interested in that.

What I like about Kunz' book is the clear distinction between science and subjective reasoning. Any species concept based on traits is declared non-scientific, because the traits used are chosen by individuals and therefore subjective. His species concept states that a species is group of organisms between which there is continuous lateral geneflow. Which brings us back to the statement: if this geneflow is interrupted (as supposed to be the case in allopatry) we can no longer speak of one species. Think about the consequences of this.
Slàinte mhath!

Uilleam

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Re: To be or not to (apart)?

Post by dogofwar » Mon Jun 17, 2013 10:10 am

Continuous geneflow is a very high standard and relies heavily on the definition of "continuous".

As an example, we collected the usual assortment of Uruguayan fish (Australoheros, Gymnogeophagus, Crenicichla, etc.) in numerous, isolated ponds in Uruguay. They seem to be (underground) spring fed and (I'd assume) get new genetic material whenever there's a flood large enough to connect them with the pond a km or two down the road or a larger river or stream. But most of the time they're isolated.

Would the frequency of periodic flooding be the main determinant for speciation? More than one flood per year = continuous = new species? ;)

Matt

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Re: To be or not to (apart)?

Post by Willem Heijns » Tue Jun 18, 2013 3:40 am

Hi Matt, good to see you here! :D

You point at exactly what my problem is with this concept. Although I must admit Kunz didn't use the word "continuous", he defines allopatry as the gene-flow being lost. Never does he mention time constraints.
But, putting this aside, would a "permanent" loss of gene-flow be cause of speciation?
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Re: To be or not to (apart)?

Post by dogofwar » Tue Jun 18, 2013 8:24 am

Very interesting topic!

A "permanent" loss of gene flow would have been the result of some change in the environment or ecosystem to prevent gene flow among populations: a seismic event or the like.

In the example of the Uruguayan pond, let's say that because of an earthquake or Global Warming or whatever, that the pond never received new genetic material from other bodies of water.

In theory, the fish in the pond would become more and more adapted/specialized to the pond...and (potentially) different than the fish in the source streams. Or maybe not.

Matt

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Re: To be or not to (apart)?

Post by Willem Heijns » Tue Jun 18, 2013 8:54 am

Exactly! And now the prize question: would this lead to new species? And why?
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Re: To be or not to (apart)?

Post by dogofwar » Tue Jun 18, 2013 3:30 pm

Of course, it depends I think on both whether the conditions of that pond (isolated population) are markedly different than the one a KM or two away.... and the characteristics of the initial fish population initially introduced into the pond.

For example, in one of the isolated ponds that we collected, I found a couple of 2-year-old Australoheros with seemingly deformed mouths (which appeared to be genetic and not caused by trauma). If - by random circumstances - a flood washed two small groups of fish into two separate ponds (from a stream)...and one of the handful of seed fish in one pond carried a trait for a deformed mouth...and none of the fish in the other pond held that gene, then one the chanchitos in one pond could become markedly different than in the other (and in the original stream, where less fit fish would get picked off). Or simply disappear as all fish become deformed and can't eat. It would also depend on what other kinds of fish were washed into the pond with them (if any).

I prefer to call them Australoheros sp. "location" rather than each a species. Clearly with the explosion of chanchito species, others differ.

The situation of having many isolated ponds is interesting in a lot of ways. For example, we visited and collected from a couple where a certain species - a tetra or cafish, for example, had become really dominant (and almost exclusive in the pond).... while a neighbor pond might have a more diverse mix of fish. From Felipe, it seems that the mix can change over time: an especially large crop of Hoplias babies one season can nearly eliminate the livebearers and tetras from a pond.

Matt

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Re: To be or not to (apart)?

Post by Willem Heijns » Tue Jun 18, 2013 3:59 pm

Of course, different circumstances will lead to adaptations. But that is not the issue. Suppose the circumstances are just about the same and adaptations cannot be observed. Would you say we have two species then? Remember: the gene-flow has been permanently interrupted.
Slàinte mhath!

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Re: To be or not to (apart)?

Post by dogofwar » Tue Jun 18, 2013 7:33 pm

I don't think it makes sense to say that they always are different species...

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Re: To be or not to (apart)?

Post by Willem Heijns » Wed Jun 19, 2013 2:18 am

Is it safe to say then, that the species as a "gene-flow community" is not a concept you would adhere to?
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Uilleam

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Re: To be or not to (apart)?

Post by Willem Heijns » Wed Jun 19, 2013 3:38 am

There's quite a few species concepts about. They either suffer from not being operational (how do you test interbreeding populations?) or from being non-scientific, i.e. dependent on subjective opinions (which traits are necessary and sufficient to define a species?).

I would prefer a concept that is at least based on obejective criteria. Even then it will be difficult to assign organisms to species, but the best we can do is to use as many traits as possible to get strong indications.
Slàinte mhath!

Uilleam

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Re: To be or not to (apart)?

Post by Lisachromis » Wed Jun 19, 2013 7:58 am

What criteria would you use?

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Re: To be or not to (apart)?

Post by Willem Heijns » Wed Jun 19, 2013 9:34 am

I'm not sure. I'm tempted to go with the concept of "species as lineages", but this concept is hard to identify. The gene-flow community sounds like a good alternative to me, but that raises the question (too many species?) this topic is all about.

But I'm in good company. I have yet to meet a taxonomist who explicitly states the species concept he/she uses when describing new taxa. :?
Slàinte mhath!

Uilleam

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Re: To be or not to (apart)?

Post by cichla » Wed Jun 19, 2013 3:52 pm

Willem,
well, I think Lisa (at least me, I like to know) is asking for 'concrete' criteria. To talk about "species as lineages" is not very helpful.
Willem Heijns wrote:But I'm in good company. I have yet to meet a taxonomist who explicitly states the species concept he/she uses when describing new taxa.
I am not sure, if I get you. Are you looking for papers where specialist mentioned the 'species concept' used?
Yours, IS

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Re: To be or not to (apart)?

Post by Willem Heijns » Wed Jun 19, 2013 4:05 pm

If I had concrete criteria, I would have published them and become famous. I also said that the "species as lineages" concept is hard to identify, meaning that I don't know any concrete direct criteria for it. That's a pity, because this concept is close to what I believe evolution is about.

And yes, I would love to see a paper with new species in it and the author stating the species concept he/she has founded the descriptions on. Can you help here, Ingo? 8)
Slàinte mhath!

Uilleam

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