A good primer on describing/identifying fish species

[bekateen]

With the recent discussions (e.g, here, here, and here) of whether or not the black & white Xingu Hypancistrus (

L066

,

L173

,

L173b

,

L236

,

L333

,

L400

, etc.) are one species or many, this article is particularly timely. Enjoy.

P.S., This article has excellent diagrams showing people the anatomical names of various fish body features and also how to measure body lengths and how to describe color patterns. I'd even suggest that it has so much helpful information in it, this paper is worth downloading and saving for future reference.

Keat-Chuan Ng C., Aun-Chuan Ooi P., Wong W.L., & Khoo G. 2017. A Review of Fish Taxonomy Conventions and Species Identification Techniques. Journal of Survey in Fisheries Sciences, 4(1), 54-93.

Link: http://sifisheriessciences.com/browse.p ... lc_lang=en

PDF: http://sifisheriessciences.com/files/si ... 3de254.pdf

ABSTRACT
Taxonomists, ecologists, geneticists or researchers from other biological fields who wish to adopt fish as a constituent of their studies often become discouraged when they find that ichthyology is a complex subject. In fish-based studies, the failure to recognize fishes as distinct biological units can lead to wrong diagnosis. Hence, this review paper attempts to clarify and discuss the latest schools of thought pertaining to fish taxonomy and the techniques for species identification. It is hoped that the contents and illustrations in this paper will assist researchers in laying a good foundation to inform their studies.

• Keywords: Fish, Morphology, Molecular, Taxonomy, Species identification

[TwoTankAmin]

Interesting read, wish it discussed plecos.

What I am drawing from all the recent discussions is basically nobody knows the facts yet. The one thing that apparently is known is that there is only one described B&W species in the Xingu, H. zebra.

I am a dunce re genetics. But it seems to me that the genetic research is incomplete, it is not sufficiently in depth to draw any conclusions. I even saw in the thread about the paper on 66 and 333 that some felt it was by no means conclusive due to the limits of what the researchers considered when doing their research. Or am I wrong on this?

And then, how much evolution is involved here? How did H. zebra come into existence. it must have evolved from something. Would that not suggest that somewhere in that evolutionary process other pleco species likely evolved from a common ancestor(s)?

The best I can come up with here would be to consider Homo sapeins. All the humans on the planet are the same species now. But then we can find Watusi people who are extremely tall, pygmy people who are very small. We have people with black skin, white skin, eyes which are described as "slanted" etc. For the most part each sub-group tends to breed true, looks in some ways distinct from each other and is readily able to "inter-breed." So genetically we are all the same species but we do not all look similar. However, Homo sapiens seems to have become the dominant (lone) species of the humans.

The species that you and all other living human beings on this planet belong to is Homo sapiens. During a time of dramatic climate change 200,000 years ago, Homo sapiens evolved in Africa........

Unlike every other human species, Homo sapiens does not have a true type specimen. In other words, there is not a particular Homo sapiens individual that researchers recognize as being the specimen that gave Homo sapiens its name.

from http://humanorigins.si.edu/evidence/hum ... mo-sapiens

Science does not even agree on from which species of the genus Homo we are descended. We may even be a hybrid from what I read.

But the human analogy I can understand. But then, since H. zebra is a described Hypancistus species, it would seem that all the other mishmash is also genetically H. zebra but one which looks different and breeds true? Perhaps another species evolved from zebra and then crossed back to give the mishmash? But somehow I do not think that the current science supports this? If no, then from where, taxonomically, do all the plecos in the mishmash originate?

This stuff is starting to make me sorry I ever moved beyond my first planted community tank

[Mol_PMB]

I got my head screwed up by all of this a couple of years back. A really important thing to remember is that 'Nature' does not recognise the concept of a species. 'Species' is an artificial invention by humans in an attempt to describe nature. It is useful, but it is over-simplified. The concept is rather 'black and white' where in fact nature is not just shades of grey but a full spectrum of colours, not all of which we can see.

[bekateen]

I got my head screwed up by all of this a couple of years back. A really important thing to remember is that 'Nature' does not recognise the concept of a species. 'Species' is an artificial invention by humans in an attempt to describe nature. It is useful, but it is over-simplified. The concept is rather 'black and white' where in fact nature is not just shades of grey but a full spectrum of colours, not all of which we can see.

As a biologist, I'd say that's both true and not true at the same time. It depends on what you mean by " 'Nature' doesn't recognize the concept of a species." It's true that humans invented the word and the definition (and therefore Nature doesn't need to recognize it), but using the Biological Species Concept, the definition is based on a measurable and quantifiable concept - the ability to share and exchange genes (and as a quantifiable concept, nature recognizes it functionally).

The biological species concept works pretty well when we ask about the ability to "successfully breed" among individuals when those individuals live among groups of similar individuals and when they collectively form a contiguous range geographically: Those who can interbreed are in the same species and those who cannot are clearly not of the same species. But even this concept allows for the possibility that we get into what you might call subspecies (which I personally don't believe in as a concept), local populations/geographic variants (which I do believe in and which are probably closest to our concept of "subspecies"), and "interspecific" hybrid zones... You should expect these local groups in nature using this definition; in fact, they are the "stuff" of evolution and speciation - the mess that forms when existent species fracture and new species form. If these grey areas are robustly fertile, then I would argue they are within the same species but are local variants/color morphs. If their fertility is at all impaired, then I would argue they are interspecific hybrids or are at the very least local populations on the verge of speciation.

From what I last read, there is a trend to talk about local populations as "evolutionary units" independent of species as a whole. That makes sense, but from a logical perspective it does not elevate them out of the species or degrade the value of the species concept.

The best I can come up with here would be to consider Homo sapeins. All the humans on the planet are the same species now. But then we can find Watusi people who are extremely tall, pygmy people who are very small. We have people with black skin, white skin, eyes which are described as "slanted" etc. For the most part each sub-group tends to breed true, looks in some ways distinct from each other and is readily able to "inter-breed." So genetically we are all the same species but we do not all look similar. However, Homo sapiens seems to have become the dominant (lone) species of the humans.

Humans are a good example of the problem, as TTA mentioned above - There exists a great diversity of geographic variation in height, shape, color, etc. But there is so much migration that effectively the group of humans as a whole is a reproductively continuous unit, and that's why we consider ourselves one species. Gene flow between phenotypes prevents us from definitively saying one group (e.g., an African tribe) is a different species from another (e.g., a native North American tribe). But the very fact that genetic services like "23 and Me" or "Ancestry dot com" exist and can tell you (with some level of significance) your geographic ancestry affirms that there are genetic differences between groups of humans.

As to the issue of synthesizing the species concept for similar phenotypes that are widespread geographically but are classified as one species, the paper above helps to explain why this is particularly complicated with fish. I'm thinking of how fish are restricted (usually) by watersheds. It's tempting to think of a widespread morph like Corydoras aeneus as one species, but if they are reproductively isolated by watersheds with little or no chance for gene flow between watersheds, then practically-speaking we probably need to bear down and say they aren't one species.

What I am drawing from all the recent discussions is basically nobody knows the facts yet. The one thing that apparently is known is that there is only one described B&W species in the Xingu, H. zebra.

I am a dunce re genetics. But it seems to me that the genetic research is incomplete, it is not sufficiently in depth to draw any conclusions. I even saw in the thread about the paper on 66 and 333 that some felt it was by no means conclusive due to the limits of what the researchers considered when doing their research. Or am I wrong on this?

The other issue that comes back to what TTA was discussing is that to date, since "biological species" are defined by reproductive isolation, which can be satisfied by something as simple and tenuous as geographic isolation, then the definition does not have as a requisite a specific amount of genetic difference to quantitatively define two populations as separate species. And that's where the problems come in for things like L066, L333, and that whole mess.

Unlike every other human species, Homo sapiens does not have a true type specimen.

In my opinion, this is not a fair statement since every other humanoid besides Homo sapiens is based upon fossil evidence. So in terms of flesh-based phenotypes (skin, hair, etc.), they really have no type specimens either. If you are going to base type-specimens for all other humanoids on a skeleton, you could choose to do the same for H. sapiens... But doing so masks our diversity.

This stuff is starting to make me sorry I ever moved beyond my first planted community tank

Dont be sorry - Complexity creates the spice of life! Without it, you wouldn't have H. zebra or anything else!

I'm sure others can take issue with my beliefs as stated here. And you're welcome to, since I don't consider myself to be the gold-standard by which species are defined. And although I'm an evolutionary biologist, I'm one only peripherally, not involved directly in the researching and writing up of work meant to advance our understanding of the concept of species and taxonomic units.

Cheers, Eric

[TwoTankAmin]

Things are making a bit more sense when I stick with the human side of it. Consider that,

Humans are most closely related to the great apes of the family Hominidae. This family includes orangutans, chimpanzees, gorillas, and bonobos. Of the great apes, humans share 98.8 percent of their DNA with bonobos and chimpanzees. Humans and gorillas share 98.4 percent of their DNA. Once the apes are not native to Africa however, the differences in DNA increase. Humans and orangutans share 96.9 percent of their DNA. Humans and monkeys share approximately 93 percent.........
Humans and mice share nearly 90 percent of human DNA.......
Humans and dogs share 84 percent of their DNA,

from http://education.seattlepi.com/animals- ... -6693.html

Dang, throw me a banana, some seeds and a Milk Bone..........

[Lycosid]

As to the issue of synthesizing the species concept for similar phenotypes that are widespread geographically but are classified as one species, the paper above helps to explain why this is particularly complicated with fish. I'm thinking of how fish are restricted (usually) by watersheds. It's tempting to think of a widespread morph like Corydoras aeneus as one species, but if they are reproductively isolated by watersheds with little or no chance for gene flow between watersheds, then practically-speaking we probably need to bear down and say they aren't one species.

I've been thinking about this watershed issue a lot. The issue seems to me to be that species designations can end up trying to predict the future. You have population A in one river and population B in another. Calling them separate species may be fine, if they stay separated geographically, but the same "species" could re-merge if the rivers change course and connect. Because waterways split and merge so much more than landmasses this problem seems to be much larger in aquatic biology than in terrestrial biology.

Unlike every other human species, Homo sapiens does not have a true type specimen.

The ICZN recognizes Linnaeus himself as the type specimen, although they put this in their FAQ page because this is apparently so poorly known.

[bekateen]

I've been thinking about this watershed issue a lot. The issue seems to me to be that species designations can end up trying to predict the future. You have population A in one river and population B in another. Calling them separate species may be fine, if they stay separated geographically, but the same "species" could re-merge if the rivers change course and connect. Because waterways split and merge so much more than landmasses this problem seems to be much larger in aquatic biology than in terrestrial biology.

True. I would expect that a watershed will be a more stable isolation mechanism in situations where elevated land masses separate drainages (e.g., opposite sides of the Andes) and will be a less reliable isolation mechanism when you have a flatter terrain where flooding is capable of connecting water ways. I'm sure there are more nuances to this, but those are a couple of extremes that come to mind easily.

The ICZN recognizes Linnaeus himself as the type specimen

Interesting.* Other than honoring him for his contribution to science in this field...

From a practical point of view the designation of Linnaeus as lectotype is of limited value, since there is no doubt over the identity of the species Homo sapiens. ... However, it is symbolic that Linnaeus as the father of modern taxonomy should have been designated. (emphasis added; same source as cited by Lycosid)

...I'm not sure I see the merits of that choice. But I'm confident someone has put a lot of thought into it, so I will hold my tongue. Needless to say, no matter which human is recognized as the type specimen, it still doesn't help when comparing humans to all other ancient humanoids which are known only from fossil specimens.

• * Good gravy! I just had a flashing image of Linnaeus sitting in a pickle jar on the shelf of some natural history museum!! {Truth be told, he isn't... It was simply an obvious inference}

Cheers, Eric

[Shane]

Something else to ponder from Wired...

"First off, this means that whenever someone asks, "Who's the man?" you should shout out, "Carl Linnaeus!"
Secondly, this means that if someday it is revealed that vampires are real – that they live among us, hiding their true natures, breeding among themselves and preying upon our blood for their sustenance – the first question that biologists will have is, "Yes, but was Carl Linnaeus one of them?"
You see, Carl Linnaeus is humanity. So if it turns out that he was a vampire, that would mean that, scientifically speaking, vampires are Homo sapiens and the rest of us are some unnamed, superficially identical species of hominid. "

-Shane

[Lycosid]

...I'm not sure I see the merits of that choice. But I'm confident someone has put a lot of thought into it, so I will hold my tongue. Needless to say, no matter which human is recognized as the type specimen, it still doesn't help when comparing humans to all other ancient humanoids which are known only from fossil specimens.

I think the main merits of this choice are to occupy that space so that someone else can't be designated as the type. Obviously Linnaeus considered himself to be human when he designated the species, so he's as close to a non-controversial choice (in the sense that by designating him we are just following the rules) as can be.

I seem to remember that people used to claim that Cope of the Cope and Marsh bone wars wanted to be the human type specimen, so I suspect it's something someone would try to get for status if it was unfilled.

[bekateen]

I think the main merits of this choice are to occupy that space so that someone else can't be designated as the type...

I seem to remember that people used to claim that Cope of the Cope and Marsh bone wars wanted to be the human type specimen, so I suspect it's something someone would try to get for status if it was unfilled.

Yes you are correct about "occupying the space." If you go back to the same page you cited above, there's at least one or two paragraphs devoted to this explanation lower down on the page.

Cheers, Eric