When is a species not a species?

[grokefish]

They can crossbreed for sure, many similar species of Hypancistrus can and will crossbreed.

Have I got this wrong or doesn't the fact that they can cross breed on their own mean that they are in fact the same species?
Matt

[Mod edit: Split the original thread into two threads. I also quoted the post that sparked this discussion into this post --Mats]

[racoll]

Have I got this wrong or doesn't the fact that they can cross breed on their own mean that they are in fact the same species?

Sadly not. Closely related species are frequently able to hybridise and often produce viable offspring.

I would expect the two to be different species, as they appear quite morphologically distinct.

[grokefish]

I know you know your stuff Racoll, but whilst reading the book "The Ancestors tale" by the world- renowned evolutionary biologist, author and shit stirer, Richard Dawkins states categorically that the very definition of species is the ability to reproduce.
What position does that put asexual organisms?
I am most confused.
Can you provide me with a definition?
I assume that there is one.
Matt

[MatsP]

I know you know your stuff Racoll, but whilst reading the book "The Ancestors tale" by the world- renowned evolutionary biologist, author and shit stirer, Richard Dawkins states categorically that the very definition of species is the ability to reproduce.
What position does that put asexual organisms?
I am most confused.
Can you provide me with a definition?
I assume that there is one.
Matt

I don't know the exact rules, but I think that is a simplification and a reversal of the rule. You can CLEARLY say that two species are distinct if they can not produce viable offspring. Reversing that is like reversing "A dog has a tail" to "if it has a tail it's a dog".

There are known viable hybrids of quite a few species of fish, including some of the Cichlids from Lake Malawi.

--
Mats

[Bas Pels]

I know you know your stuff Racoll, but whilst reading the book "The Ancestors tale" by the world- renowned evolutionary biologist, author and shit stirer, Richard Dawkins states categorically that the very definition of species is the ability to reproduce.
What position does that put asexual organisms?
I am most confused.
Can you provide me with a definition?
I assume that there is one.
Matt

Many definitions of species are given, but in my opinon they all fail

almost all Central American cichlids can be crossed, and the offspring can reproduce themselves. Thus, acoording to Dawkins they are all 1 species

The problem is, some species feed on others, thus they are cannibalistic?

ecosystems consisting of a dozen varieties of 1 species?

I think nature does not work with species, but works with more or less seperated populations, gene pools, and individuals. Species is a human invention, i order to understand at least some thing of nature, but it is a model, not the reality

[corydoras]

Hi

You only have to look at the liverbearer world to see that hybrids can be viable, swordtails and platies for instance. Also the molly species can easily hybridise with each other. There are even viable Skiffia hybrids.

Matt

[racoll]

Can you provide me with a definition?

The species concept is one that has troubled biologists for a rather long time, and will definitely continue to do so for the foreseeable future. Bas Pels stated the problem with species concepts quite nicely.

Dawkins knows more than most on the subject, and I've not read that book, but it seems that he is still a proponent of the "biological species concept" whereby species are diagnosed on the basis of not being able to interbreed. While not being able to interbreed is a strong signal for two species being "good", and therefore significantly divergent, there are many species that have not diverged enough to be reproductively isolated.

It is generally considered an outdated approach, with the main problem being that it is pretty much unworkable. It is not really practical to carry out studies to test species boundaries by trying to breed them. Most taxonomists have neither the time or money to carry out this kind of research.

Nowadays most people accept the "phylogenetic species concept" as the best working model of the species problem. It is based upon recognising species as lineages with shared unique characters. This assertion is formulated with computerised cladistic analysis, but is only as good as the characters that are put into the analysis. A side effect of this concept is the recognition of sometimes considerably more species than previously (i.e. subspecies or distinct populations). This is not always popular with conservationists, but does reflect diversity in a much more rigorous, testable and repeatable way.

Some links.
http://wiki.cotch.net/index.php/Phyloge ... es_Concept
http://wiki.cotch.net/index.php/Species
http://en.wikipedia.org/wiki/Species

[grokefish]

As I thought a definition is not possible, as Bas says nature does not work to Human ideas, or something like that.
Doesn't it mean therefore that this whole thread is a nonsense (Sorry Daragh I don't mean to hijack it) as the individuals L066 and L333 are in fact the same organism as they can in fact produce offspring, so as far as nature, in the form of the fish themselves, is concerned the labels L333 and L066 are pointless and Daragh need not separate them at all but consider them as " A number of the same type of fish"
Do you think this is a similar case to the salamanders in that valley in California?
I have two dogs, one has a tail and one does not. They are called Bumpy and The Pig
Matt

[Bas Pels]

As I thought a definition is not possible, as Bas says nature does not work to Human ideas, or something like that.
Doesn't it mean therefore that this whole thread is a nonsense (Sorry Daragh I don't mean to hijack it) as the individuals L066 and L333 are in fact the same organism

I'm afraid organism is the wrong word. Organism refers to an individual, and if I see 2 cats, most of the time, there are 2 cats (the rest of the cases I had a few drinks too much )

However, L066 and L333 are not identical: they come from another place and thus they might be very similar varieties, but personally, I would try not to breed differnet varieties

as they can in fact produce offspring, so as far as nature, in the form of the fish themselves, is concerned the labels L333 and L066 are pointless and Daragh need not separate them at all but consider them as " A number of the same type of fish"

This is the problem with the L number system: of a loricarid is found in a certain location, and does not look like any loricarid knowm from that location, it will, ultimately, get its own L number. Somoetimes an L number is used which was not available, sometimes many L numbers are given to 1 species.

L200 is a very nice example. 2 species, looking alike, are shared under it, (we now have a highfin L200 and a lowfin L200 ) but L128 is seen as very closely related to one of them, perhaps the same species. On the other hand, it does also have its advantages: should one look for a certain fish from a certain place, the L number is more specific then a species name

Do you think this is a similar case to the salamanders in that valley in California?
Matt

unfortumately, I don't know this salamander. It could be a very good example, though - or not

[MatsP]

So, according to the principle of "able to reproduce together", this

Hypancistrus sp_hybrid

is the same species as

Hypancistrus sp(L066)

and

Hypancistrus sp(l136)

. [Assuming, of course, that the offspring is fertile - we don't know, and I don't think we want to figure that out either].

It's not entirely unlikely that

Hypancistrus zebra

and other Hypancistrus can cross-breed [likely with viable off-spring].

Does that also make them the same species?

--
Mats

[Suckermouth]

Do you think this is a similar case to the salamanders in that valley in California?
Matt

unfortumately, I don't know this salamander. It could be a very good example, though - or not

The salamander being referenced is probably Ensatina eschscholtzii. It is an example of a ring species in that each subspecies can interbreed with neighboring subspecies, forming a ring around the mountains in California.

The ability to reproduce alone and produce viable offspring alone is not a viable way to define species. Species that live in the same area can easily be defined this way, as if they were to interbreed they would have done so long ago. However, with species that are geographically isolated it is more difficult. Lions and tigers can hybridize, but no one considers them the same species. However, with L066 and L333, the differences are not as apparent to us (which doesn't meant they're not there, it just means they're not apparent). What level of difference, then, is great enough to consider two "populations" different species? As far as I have seen from looking at scientific papers, taxonomists validate different species with not only location, but also morphological (ie. shape, pigment) and meristic (counts, ie. fin rays) differences. Genetic differences are not widely used yet, although they've been used in the paper of at least one species of fish so far. It could be, with more study, that L333 and L066 are in fact different species due to differences above coloration. I can't think of a diagnoses off the top of my head of any species based exclusively on coloration of fish, so if these fish are different species they may have other differences too.

[MatsP]

Do you think this is a similar case to the salamanders in that valley in California?
Matt

unfortumately, I don't know this salamander. It could be a very good example, though - or not

The salamander being referenced is probably Ensatina eschscholtzii. It is an example of a ring species in that each subspecies can interbreed with neighboring subspecies, forming a ring around the mountains in California.

The ability to reproduce alone and produce viable offspring alone is not a viable way to define species. Species that live in the same area can easily be defined this way, as if they were to interbreed they would have done so long ago. However, with species that are geographically isolated it is more difficult. Lions and tigers can hybridize, but no one considers them the same species.

Albeit all Tions and Ligers are sterile, so the offspring is not viable and they are not "successfully reproducing".

But you are right, if the species are not geographically separated, any crossbreeding would "mix the species into one".

--
Mats

[grokefish]

Thats exactly the question I am asking, you must remember I am not asking these questions because I am trying to prove or disprove a point or make it sound like I am very knowledgeable but because it is a field that I have only just become interested in and am trying to milk you guys, that really know your stuff, for information, people that I trust to provide me with information and opinions that are valid and informative.
For example the hypancistrus.
If these fish met in the wild and bred together, as has been proved that they can, would their offspring eventually become a separate "species" or are they still just hybrids. How long does it take for these hybrids to become a new species?
Also, as we are in fact part of nature itself, in the bigger picture are these tank bred hybrids not valid as a different species anyway? just not in the conventional sense of a natural species but in extension of nature created by man that is in fact part of nature.

How does it work with cows and horses?
Is a Jersey cow a different species to a the black and white ones that I don't know the name of?


Matt

[MatsP]

All horses, cows, pigs, guinea pigs, rats, dogs, are one species (each - cows are obviously not the same species as dogs! ). Yes, they do look fairly different, when comparing a miniature horse with one of those old "working" horses that pulls beer-kegs (Ale-kegs) from the Young's brewery in London, that's for sure. But they are, according to current science, the same species. Chiuaua's and St Bernards too.

As to "when does a hybrid become a species" is another question - I'd say "when science accepts them as a species", which in the case of tankbred varieties probably means "never".

The reason the species have developed is generally that they do NOT meat in nature - the different forms of L066, L333 etc come from slightly different places in the same region - so they have probably fairly recently split off from the same branch of the evolutionary tree.

--
Mats

[Suckermouth]

Albeit all Tions and Ligers are sterile, so the offspring is not viable and they are not "successfully reproducing".

I have heard the females are fertile while males are sterile... Not that it's an important point.

Wild hybrids do occur, but if I'm not mistaken usually the species remain distinct. However, there have been problems with a species becoming extinct because there are two few of that specific species, so they hybridize with a more abundant, related species. Basically one species becomes part of another species. No new species is created or would be named.

As I see it a hybrid can't become a species in its own right. Rather, it would result in lumping of two species together, one species becoming the taxonomic synonym of the other.

[racoll]

As I thought a definition is not possible

You might have misunderstood what I meant here grokefish. A definition is possible (the phylogenetic species concept - PSC), and although no definition is perfect, it works very well.

There are always exceptions, but generally these are in the minority, with most species being "good", and easily diagnosable to a trained eye. Hybridisation is by no means a common phenomenon, as it carries with it the potential for significant evolutionary disadvantages.

individuals L066 and L333 are in fact the same organism as they can in fact produce offspring, so as far as nature, in the form of the fish themselves, is concerned the labels L333 and L066 are pointless

No, under the PSC, these are likely to be different species. They have clearly different morphologies. Now you may wonder what constitutes an appropriate character to use in phylogenetic analysis and the diagnosis of new species. This is up to the individual taxonomist and his experience with the group, but remember journals are peer reviewed, so it is unlikely a load rubbish will get published.

I can't think of a diagnoses off the top of my head of any species based exclusively on coloration of fish, so if these fish are different species they may have other differences too.

Funnily enough, they most recent description (Armbruster et al, 2007) of four new Hypancistrus (L201, L129, L199 & L339) from the Orinoco was almost entirely based on colour pattern characters. The pattern and colour of Hypancistrus is likely to be highly valuable in the distinction of further new species, but the problem and skill is turning the diversity into sound and reproducible cladistic characters.

genetic differences are not widely used yet, although they've been used in the paper of at least one species of fish so far

The use of molecular characters by systematists is a very useful and powerful tool, but unfortunately the history of a gene is not necessarily the history of a species, and to reveal the true phylogeny, many many genes should be studied, which can be expensive and time consuming. Much of the difference between closely related species can be identified by a trained eye, so it is generally better to use molecular techniques to answer more complicated questions across higher taxonomic levels.

Having said that, the Hypancistrus of the Rio Xingu would be excellent candidates for using a molecular study to get a handle on how significant colour/pattern can be in species delimitation.

[grokefish]

Cool, I think I understand more now but am still Baffled as to the point of it all.
Matt

[Birger]

Cool, I think I understand more now but am still Baffled as to the point of it all.
Matt

I am not a real great debater...and I like to simplify things but the point for me as a hobbyist is there are so many cool varieties out there why would a person want to throw them all in a bucket and just take out what survives......a silly analogy to go along... there are many colors of paint...if you throw all those colors in a bucket you usually end up with a really ugly brown

Birger

[andywoolloo]

ok i read this whole thread and wow.

are most of u scientists or something? it's amazing the info on this site.

[Suckermouth]

Funnily enough, they most recent description (Armbruster et al, 2007) of four new Hypancistrus (L201, L129, L199 & L339) from the Orinoco was almost entirely based on colour pattern characters. The pattern and colour of Hypancistrus is likely to be highly valuable in the distinction of further new species, but the problem and skill is turning the diversity into sound and reproducible cladistic characters.

Oh my, I did actually read that paper. I was quite excited when it was published; Hypancistrus has such obvious diversity, and up to then there were only two species. Was waiting on a scientist to just jump on it and start working! Reviewing the paper, you're right, it does say that the species can't be distinguished morphometrically, and that differences were primarily in coloration; the diagnoses of species is almost entirely on coloration, only using the dorsal fin length to differentiate a few of the species. So it appears I just happened to forget the most relevant species to this topic, lol. It appears that in the discussion, Armbruster mentions Lasiancistrus is similar in that species are differntiated primarily by coloration, and claims Peckoltia vittata-like fishes also fall into this category. So it seems in Loricariidae coloration alone can in fact define species, but as he admits, coloration is not usually a satisfactory characteristic for species description.

I'm also remembering that many of the Pseudoplatystoma species are also best distinguished based on coloration...

Having said that, the Hypancistrus of the Rio Xingu would be excellent candidates for using a molecular study to get a handle on how significant colour/pattern can be in species delimitation.

A molecular study including many of the Hypancistrus "species" would be one hell of a paper. That'd be a pretty sweet read.

are most of u scientists or something? it's amazing the info on this site.

I can't speak for the others, but I'm not a scientist. I'm just an undergrad Bio major who likes to pretend he's a scientist, lol. I do find catfish taxonomy fascinating though, and, with my university access (woohoo!), I've "read", or at least looked over or skimmed, many of the recent papers that have been published about new species; these include a number of H. H. Ng's, who if I'm not mistaken is Silurus. And when I said "read", I mean only as much as a person who doesn't know all the skeletal parts of a fish can possibly read, anyway.

[andywoolloo]

very cool!

[Mike_Noren]

Ability to interbreed is a primitive trait inherited from a common ancestor, and as such is not indicative of species status.

INability to interbreed is a derived trait, and as such indicative of species status.

In other words, if two groups of animals are able to interbreed and have fertile offspring, this provides no information on whether they're the same species or not. However, if two groups of animals are NOT able to interbreed and have fertile offspring, it means they're separate species.

Note that inability to interbreed is not the only diagnostic criterion on species; that the members of the group are more closely related to eachother than to any other group is another criterion, as is the presence of unique derived traits. In reality, the presence of sufficient unique derived traits is normally the only information available to the taxonomist describing the species, meaning it's the "de facto" species concept.

Note that there exist no sharp divide between population and species. They imperceptibly grade into eachother, meaning you'll occasionally find instances where it is completely subjective whether the group of animals is a population or a species. These cases are often cases of incipient speciation.

As the concept of species is based on exclusivity in sexual reproduction, the species concept(s) breaks down for clonal organisms like e.g. bacteria which do not have sexual reproduction. There does not, to the best of my knowledge, exist any species concept which works well for such organisms.

[ncanavan]

This is worth are read if like me, you find this area fascinating:
http://www.pnas.org/cgi/content/full/102/suppl_1/6600
Niall

[Shane]

Cool, I think I understand more now but am still Baffled as to the point of it all.

Although a statement, this is actually the key question. People often confuse taxonomy, classification, and systematics. Taxonomy is the science of classification. Systematics is the study of the diversity of life. The purpose of systematics is to understand the evolutionary history of a group.

Taxonomy focuses on identifying, naming, and classifying organisms.
Systematics focuses on placing organisms in groups that show their relationship to other organisms.

The research that comes from taxonomy and systematics becomes scientific classification.

The three fields are all intricately tied together and many scientists do both. Jon's above description of new Hypostomus is clearly taxonomy, while some of his past work on defining the genera of the family loricariidae is clearly systematic in scope.

Understanding the above is key to understanding why the issue of two "species" that can or can not interbreed is only relevant for what it demonstrates about their shared evolutionary history. It does not represent and ends, but rather a means by which we can further understand the evolutionary relationship of the organisms in question.

The point of it all is thus to understand how every organism (past and present) relates to every other organism and where they fit in the evolutionary history of all life that has come and gone on this planet.
No small topic when you realize that this is the only time and space in all infinity where we have found and can study life.
-Shane

[racoll]

In addition to what Shane has written, I would like to clear up another misconception about taxonomy and systematics.

Many people see the shifting of names as pedantic or as a nuisance, and taxonomy as a "lesser science" due to its historically descriptive nature. The name systematics is often used instead, as taxonomy is frequently considered a "dirty word".

However, the placement of species names and classifications are only hypotheses of relationship, to be subjected to test as future theories and techniques are developed and explored. Many people do not understand this basic concept.

I think nature does not work with species, but works with more or less seperated populations, gene pools, and individuals. Species is a human invention

Coming back to this central point, many disagree with this idea, which often stems from the confusion between traits and characters. This excerpt from Wheeler (2007) describes it well.

"Many who were educated in the context of the New Synthesis believe that genetic variation is essentially continuous in Nature. This emerged in part from the focus on population genetics and the emphasis of studying the origin and distribution of mutations within and among populations. The confusion was deepened by Mayr (1942, 1963) and others who, whether by accident or design, conflated tokogenetic patterns and phylogenetic patterns. This failure to distinguish between “traits” and “characters” (in the strict sense of Nixon & Wheeler 1992) reinforces the belief that species boundaries are artificial ones of convenience. Were species merely arbitrary, then approaches like DNA barcoding would be more serious alternatives to good taxonomy; but they are not. Species emerge when traits and characters are differentiated and patterns of distribution of the latter are critically analyzed. It is disingenuous to point to traits that are polymorphic within species as evidence that species boundaries are subjective when there are unique combinations of constantly distributed characters distinguishing species, at least those formulated by pattern criteria, such as the Phylogenetic Species Concept (e.g., Wheeler & Platnick 2000)."

No small topic when you realize that this is the only time and space in all infinity where we have found and can study life.

Indeed. Life is a pretty amazing thing, and I for one find all creatures and plants eminently more beautiful and intriguing than any work of art produced by the hands of man.

[apistomaster]

This is one of the most complex issues aquarists ever try to come to grips with. It isn't straight forward like water chemistry. Biology is a messy science and process and racoll has explained most of the reasons why as well as most anyone can.

As many of the members are aware, I have been involved with Symphysodon species(The Discus) for four decades.
Recent molecular genetic work has shown that the genotype of S discus Heckel and S. haraldi are essentially indistinguishable.
Yet clearly they are two different species. Their hybrids are semiviable. Rarely have the hybrids been bred past F3 successfully and each is adapted to a peculiar biotope.

Then their is the case of the North American native Cutthroat trouts. About 14 recognized subspecies, geographically isolated but all can freely interbreed given the opportunities with each other and produce viable progeny. The native Cutthroat also coexists in areas where the natural ranges overlap with native Rainbow Trout but the two do not hybridize. Where the two have been introduced, hybridization is common and the progeny(known as Cuttbows) are fully fertile and the phenotypes can run the entire continuum from identical to either species and every gradation in between.

There may never be a definition of of a species that satisfies all situations or interested parties but it is a way to impose some order to allow these things to be discussed within some boundaries however elusive the limits may be.

[grokefish]

I see.
Matt

[racoll]

Recent molecular genetic work has shown that the genotype of S discus Heckel and S. haraldi are essentially indistinguishable.

Not exactly. They (Ready et al 2006) only analysed two genes. The phylogeny of a gene is not always the phylogeny of a species. If the whole genome of these two species were studied, I'll bet they are distinct.

[Bas Pels]

" Were species merely arbitrary, then approaches like DNA barcoding would be more serious alternatives to good taxonomy; but they are not. Species emerge when traits and characters are differentiated and patterns of distribution of the latter are critically analyzed. "

Although I would have preferred the use changes instead of species, but I do agree this is the essential problem with species/ changes.

DNA tests can tell one about the amount of similarity, they can even tell what the changes are between two samples, but they can never decide whether we should decide to consider both samples as one species or not.

My eyes are greenish, my brother has brown eyes. There is de genetic reason for this differences, and thus we differ genetically. Still, this small change between our DNA will not decide whether we are 1 species or not

Research has shown very small changes in DNA can make fruit flies grow multiple legs, (I read on the science page of a paper, a long time back). This change in DNA might be hard to detect, but 4 legs or 6 will decide about tribes, not classes

We share 98 % of our DNA with chimpanzees. However, what does this DNA do? Does it translate into proteins or does it decide what proteins to translate? A large part of our DNA does not have any meaning (we know about, I should say) so if we would only differ in this DNA, we would have been chimpanzees.

Once I read a book defending the theory that we are more related to orang utangs than chimpanzees - because the Asian rainforest is so much different from the African, that the orang had to adapt - and this adaptation, which has nothing to do with relatedness, was supposed to explain the differences between orang and human.

Be that as it may, it does introduce the way systematics would properly be executed - we see a lot of different animals, and try to trace back their evolution. In this attempt we see evolutionary groups which change a lot and others remain basically the same, but this can make them less similar, but not less related.

Therefore, DNA might be a very useful tool, but still some expert will need to decide whether the found differences have any meaning or not

[tzwms]

" Were species merely arbitrary, then approaches like DNA barcoding would be more serious alternatives to good taxonomy; but they are not. Species emerge when traits and characters are differentiated and patterns of distribution of the latter are critically analyzed. "

DNA tests can tell one about the amount of similarity, they can even tell what the changes are between two samples, but they can never decide whether we should decide to consider both samples as one species or not.
. . .
Therefore, DNA might be a very useful tool, but still some expert will need to decide whether the found differences have any meaning or not

I can't say that I agree completely with either one of these positions. As pointed out earlier in this thread, species are defined sometimes by physical differences and sometimes by only color. Either one of these is based on the opinions and prejudgious of the person doing the assigning. DNA is a serious tool in taxonomy and is being used today. As you are probably aware there is DNA Barcoding effort being carried out on a worldwide basis to characterize all animals and plants based on differences in mitochondrial DNA. It was recently the basis for making the determination that there are 4 species of snow leopard rather than one. DNA Barcoding isn't being done in a closet as it uses traditional taxonomy to build its database. In the future it is quite reasonable to assume that DNA Barcoding will play a bigger and bigger role in determining if there is sufficient differences in two populations to warrent calling them different species. And this last brings us back to the fact that species are a human artifact and as such you bring all of the data together, distribution, morphology, physiology, color, DNA data, et etc and some expert makes the call.
Just my 2 cents worth