I was wanting to know what makes a speice? I received some Ellasoma zonatum from South Carolina, and knowing that Indiana has E. zonatum, what makes them the same speices that far apart?

A species is a group of organisms capable of interbreeding and producing fertile offspring. Technically. That's how Charles Darwin wanted species defined. But people decided that if two things never encounter one another in the wild, if they live in two completely separate places and do not interact without human interference, it's a separate species.

Take Xiphophorus hellerii and Xiphophorus maculatus, for example. The two look different, yes, but they can interbreed and have fertile offspring. In fact, all of the "swordtails" and "platies" you buy in pet stores are hybrids of both. That's how the deep red color got created; the hybrid of both hellerii and maculatus had a much redder red than the reddest color of the pureblood of either species. But the two never interbreed in the wild, and they look pretty different, so people consider them different species.

Picture of wild Xiphophorus hellerii: http://www.aquarium-...ushelleri2b.jpg and http://www.fmueller....elleri-pair.jpg
Picture of wild Xiphophorus maculatus: http://gato-docs.its...fish/jp163a.jpg
Hybrid, with the red trait selected for: http://www.fishesnin...wordtail_01.jpg

The hybrids lose the long body type that X. hellerii is known for unless that, too, is selected for during breeding.
Half way hybrid: http://www.wetwebmed...n female MD.jpg
Long bodied, fully red fish we call a "swordtail" ("Xiphophorus helleri"): http://merlinmarina....ordtail_red.jpg
But you'll see it's not quite as long as its wild type hellerii relative: http://www.fmueller....tted-male-2.jpg

Anyway, my point is, what makes a species is that it can create offspring within the species that are fertile and that this offspring would be born in the natural setting. If the two would never encounter one another in the wild, then that starts to become sketchy as to whether or not that's the same species. If one regional variety has a morphological difference when compared to another regional variety, then you could make the case that that is a different species or that they are different subspecies. Come to think of it, this one time they differentiated this one species of birds into two different regional species or subspecies because they made different calls, and the birds from the one region didn't recognize the identical looking bird's call from the other region.

In my opinion, if it can fertilely breed with one another, it's the same species (maculatus and hellerii should be subspecies of the same species). But I'm not important enough for my opinion to count. *shrugs* So you get your hellerii and your maculatus being different species.

Edited by EricaWieser, 20 February 2011 - 11:02 PM.

E.zonatum from the Atlantic slope rivers and those from the Gulf of Mex rivers will probably get split into different species, so I'm told by another NANFA member studying Elassoma evolution. Since the "Type Specimen" was from the AR, the Atlantic slope ones will need a new name.

You've touched on a big ongoing debate. There are multiple competing species concepts out there. The one Erica is talking about is the biological species concept, which was formally laid out by Ernst Mayr in the mid-twentieth century. It sounds good but has a lot of problems. For example, two populations may interbreed in captivity but not in the wild (like the Xiphophorus she mentioned), or may interbreed only in human-disturbed habitats (like green and barking treefrogs). Or, two populations may interbreed frequently but still maintain themselves as distinct in areas where they live together (many sunfish, minnows, toads, etc.). Populations that appear to be the same may be separated by barriers to gene flow, so they have no opportunity to interbreed- think of darters in tiny headwater streams; the chances of them moving downstream into a river and then back upstream into a different headwater to interbreed with another population are very slight. Two populations may interbreed freely in one area of contact and not at all in another area of contact (e.g., longtail and three-lined salamanders). And of course, it doesn't work at all for the many organisms that reproduce asexually.

Prior to the introduction of the biological species concept, the major species concept was the morphological species concept. The basic idea behind it is that if you can tell them apart, they are distinct. Traditionally, morphological characters were used for this, but more recently genetic markers, physiology, behavior, habitat, chromosome counts, etc. have been used as well. Experts working on the groups at hand decide which characters are important. There's no real theory behind it and no contemporary scientist will come out and say he supports this model, but it is still the most often used species concept because it is the most practical.

The phyletic species concept tried to remove the subjective aspect of the morphological species concept by looking at lots and lots of characters and deciding relationships based on overall similarity; for example, two populations with 95% of their characters the same were more closely related than two populations that shared only 90% of their characters. This approach is now rare because it fails to take into account things like character state polarity (what character state the ancestor of the group had), convergence, etc.

The phylogenetic and cladistic species concepts (I've been assured they are different but I can't tell you the difference) are the concepts typically employed in current taxonomic research. They have some similarities to the morphological species concept, but look at characters in the context of evolutionary history. So, where a researcher following the morphological species concept might unite sharks and sturgeons because they both have heterocercal tails, spiral valves in the gut, and cartilaginous skeletons, a researcher following the phylogenetic species concept would not unite them because the first two characters are primitive characters that other fishes have lost, and the last was derived independently in the two lineages.

The evolutionary species concept goes one step further and identifies populations as species based not only on differences but on "evolutionary trajectory", or the likelihood of the population remaining distinct and further differentiating itself in the future. Like the biological species concept, this one looks good on paper but is difficult to apply.

That's probably more than you wanted to hear, but there is no simple answer to what defines a species. E. zonatum is currently defined under the morphological species concept; when researchers look at it again using other species concepts, the taxonomy may change.

I'll leave this one alone except to say I've seen ten page flame wars on other forums regarding this topic - and that's just among academics

Species is essentially a human invented concept that can't be contained easily in one sentence or paragraph and which Nature itself does not recognize.

Species exist in nature, they're just not always obvious to us as humans.

To me Mike's and Bruce's two statements are two sides of the same coin, and not even contradictory (at least for sexually-reproducing animals). I say this because "boundaries" between species are often blurry, not discrete, with varying frequencies of "intergrades" or "hybrids", and neighboring populations are often in transition either diverging farther (less mixing) or reuniting (more mixing) after temporary separation. Regarding plants, protists, bacteria, etc I'd have to agree more with Mike.

Fundulus: Species exist in nature, they're just not always obvious to us as humans.

MikeZ: Species is essentially a human invented concept that can't be contained easily in one sentence or paragraph and which Nature itself does not recognize.

I'll leave this one alone except to say I've seen ten page flame wars on other forums regarding this topic - and that's just among academics

Species is essentially a human invented concept that can't be contained easily in one sentence or paragraph and which Nature itself does not recognize.

i agree, on the human concept.
lake victoria in africa has some 400 new species of cichlids alone.
from the original 5 in the last 14000 years.
some how nature always finds a way to survive and regroup.
this one may never find a ending story

Edited by CATfishTONY, 21 February 2011 - 03:50 PM.

As far my comment re nature doesn't recognize species, I just mean that blurred line that makes a one sentence definition so tough. Sometimes stuff we call different species successfully reproduce in nature and sometimes what we call the same species do not, or choose not to. Doesn't count when they're made to breed together in captivity.

I don't want to derail this. My opinion re species has been formulated mostly from studying snakes. Milksnakes in particular have always been an interest of mine. The species Lampropeltis triangulum, according to the books, is found from Maine to Honduras and beyond. The actual animals between those extremes in range are quite different in morphology, behavoir, habitat,etc. By looks alone, there could be a dozen or more different types. Sometimes they intergrade when found together but sometimes they don't. One thing is true though, if you put a pair together in a cage, they produce fertile offspring even if it never happens in the wild.

So a "basic" is what makes a species a species (to us). Be it the number of scale lines, fin spines or whatever. Wheather it is here in Indiana or South Carolina or Florida's panhandle or where ever they occure naturaly. It could have some differences between populations within that species and remain a singal species? Or at that point is it a subspecies?

I think "subspecies" or "variety" or "race" or "evolutionarily significant unit" are all just different ways of describing intermediate stages of speciation (evolution of new species), which may be presently moving farther apart, together, or more-or-less static. There are many opinions and theories for what level of difference is meaningful to recognize and where to draw the lines, and they vary among different groups of critters depending on how they reproduce and disperse. It makes sense to apply different theories and criteria to critters with a fairly small home range, limited dispersal, and one-to-one mate selection, like milksnakes and pygmy sunfish, as compared with migratory animals like striped bass or Pacific salmon, broadcast-breeders like corals and oak trees, and organisms with non-sexual reproduction or self-fertilization.

I am with mikez concerning the statement that nature does not recognize species. There simply is no definition that is not problematic, and for good reason. The species concept tries to define some distinction between two population lineages. Yet no matter which distinctions you choose the differences within a group can exceed the differences between defined populations. Even with the most liberal use of the fertile offspring definition runs into more serious problems than different species being grouped as the same.

Consider the Ensatina salamanders (ring species). The ancestral population expanded south out of Oregon and down around each side of the San Joaquin Valley. They can interbreed anywhere along their migration route, but where they meet again at the southern end of the San Joaquin Valley they can no longer interbreed. So A and B, B and C, and C and D are all the same species. Yet A and D are not the same species.

In fact the only way to define hard distinctions between species is for the line to be so fine that parents can give birth to non-identical offspring of a different species. This is, at least in principle, possible with the cladistic species concept. But this system fails due to a linear lineage between parents and offspring. It makes sense given the lineage of a given individual, but fails when population genetics, continued local intermixing, is involved. Hence, whether you define the population of Ensatina salamanders, species A, at the northern edge of the San Joaquin Valley to split into species B and C on each side, or A continues on one side or the other while species B splits down the other side becomes a purely arbitrary choice, with no genetic meaning. Hence this definition cannot even distinguish if there are two or three species involved, much less what species any given individual belongs to in the split region.

In effect a completely self consistent definition of species becomes impossible, unless every individual of every species is its own distinct species. That of course moots the utility of the species concept. It is only natural, as evolution does not work the way it does in the movies (crocoduck?). If all offspring are the same species as the parents, then after some time when the future offspring are so different from past ancestors to qualify as a different species, there is no point at which speciation occurred without parents giving birth to a new species. Speciation is a purely relative concept.

Yes, ring species show that local populations can shade one into another until they're not the same. That doesn't eliminate species as a concept, it's just one wrinkle on how nature can vary. Species exist, but not always within the same concept. The Biological Species Concept often works, but even with some sexually reproducing groups like salamanders it gets dodgy. You can move on to concepts that don't depend on reproductive isolation like the Evolutionary or Phylogenetic, looking at shared patterns of ancestry and some form of synapomorphy(ies). Species do exist in nature, it's not always immediately obvious to us as humans that they do. That's our limitation, not nature's.

Yes, ring species show that local populations can shade one into another until they're not the same. That doesn't eliminate species as a concept, it's just one wrinkle on how nature can vary. Species exist, but not always within the same concept. The Biological Species Concept often works, but even with some sexually reproducing groups like salamanders it gets dodgy. You can move on to concepts that don't depend on reproductive isolation like the Evolutionary or Phylogenetic, looking at shared patterns of ancestry and some form of synapomorphy(ies). Species do exist in nature, it's not always immediately obvious to us as humans that they do. That's our limitation, not nature's.

It seems to me,then, that any species is mostly and idea on where we put a living organism.

No, I'd say that species are real and exist in nature. But they don't arise, and remain separate, the same way(s).

If we move on to Evolutionary or Phylogenetic systems the same problem results when you consider dynamics of population genetics. Because the gene transfers from parent to offspring over time radiate out from particular locations, two populations on each side of the valley can trade genetic information without any direct contact between members in each of those locals. This means that on occasion individuals can be more closely related (genetically) to a group they or their parents never had any direct contact with than their own local group. This merely becomes increasingly rare the farther apart the groups are. It is essentially the same quandary created by the cladistic species concept. It is like asking how soon after the wolf eats the rabbit does the rabbit become the wolf. There is not even a linear relationship between genes and traits, and genes are not a code in themselves.

I would agree that the species concept is a necessary tool. But it is merely a definition of convenience. Hence any validity it has is a tautology, which has no real physical meaning outside that tautology. Like saying the length of string A is the length of string A. Amazing what can be accomplished by taking such silly realizations seriously. Tautologies can be very powerful tools, such as mathematics where if A then Proof: X. But it is only valid because we simply defined A as true (axiom) without any further judgment about the validity of A. Coordinate independence makes things even weirder.

Yet the species tautology falls short of the idealized logical tautologies used in mathematics. Because no matter what definition you choose you can counter the validity of that definition with the definition itself. It is like saying A is true, therefore proof: A is false. But if it is false you failed to prove it was false because the proof depends on A being true. Then again this is not unique. In the bigger picture, as Gödel proved, no system of logic is perfectly self consistent. This problem of self reference underlies nearly all modern logical puzzles, and likely plays a highly significant role in issues underlying Quantum Mechanics. Such as in the relational interpretation of QM.

Enough mind bending. But the fact remains the very real utility of the species concept does not provide it with any real significance outside the tautology chosen to define it.

Thanks Mywan - Now I understand perfectly what a species is. |;>) GBP

If we move on to Evolutionary or Phylogenetic systems the same problem results when you consider dynamics of population genetics. Because the gene transfers from parent to offspring over time radiate out from particular locations, two populations on each side of the valley can trade genetic information without any direct contact between members in each of those locals. This means that on occasion individuals can be more closely related (genetically) to a group they or their parents never had any direct contact with than their own local group. This merely becomes increasingly rare the farther apart the groups are. It is essentially the same quandary created by the cladistic species concept. It is like asking how soon after the wolf eats the rabbit does the rabbit become the wolf. There is not even a linear relationship between genes and traits, and genes are not a code in themselves.

I would agree that the species concept is a necessary tool. But it is merely a definition of convenience. Hence any validity it has is a tautology, which has no real physical meaning outside that tautology. Like saying the length of string A is the length of string A. Amazing what can be accomplished by taking such silly realizations seriously. Tautologies can be very powerful tools, such as mathematics where if A then Proof: X. But it is only valid because we simply defined A as true (axiom) without any further judgment about the validity of A. Coordinate independence makes things even weirder.

Yet the species tautology falls short of the idealized logical tautologies used in mathematics. Because no matter what definition you choose you can counter the validity of that definition with the definition itself. It is like saying A is true, therefore proof: A is false. But if it is false you failed to prove it was false because the proof depends on A being true. Then again this is not unique. In the bigger picture, as Gödel proved, no system of logic is perfectly self consistent. This problem of self reference underlies nearly all modern logical puzzles, and likely plays a highly significant role in issues underlying Quantum Mechanics. Such as in the relational interpretation of QM.

Enough mind bending. But the fact remains the very real utility of the species concept does not provide it with any real significance outside the tautology chosen to define it.

Enough mind bending. But the fact remains the very real utility of the species concept does not provide it with any real significance outside the tautology chosen to define it.

I hope this is all an elaborate charade.

Of interest to the discussion. Gray tree frog Vs. Cope's gray tree frog. http://en.wikipedia..../Gray_tree_frog Visually identical,different calls, cannot interbreed due to differing number of chromosomes.

Ouch this makes my head hurt !
So a species can be same through out a large range, look different but still be the same (South Caroline -Indiana). I had gotten some E. zonatum from Lousiana some time ago and they were more of a gray/brown molt, South Carolina's had greenish bars, but I don't know what Indiana's has(Yet).
I have had no education on this just an interest that makes me ask questions and I thank you all for helping me get a better grasp on lives path.

Edited by baker46947, 26 February 2011 - 09:13 AM.