speciation vs geographical variance

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speciation vs geographical variance

Post by m1ke715m »

so anyone that keeps africans knows that alot of fish are the same species but different geographical variants where only the colors and depth found are different.. (aulonocara stuartgranti for example)

i havent seen this much in catfish im speaking mostly of loricards.. i see alot of fish considered a completely different species when they look different.. is there a reason for this? are there hypancistrus, for example, that are the exact same that migrated elsewhere and evolved into having different stripes etc? or do they just speciate into a completely different species?
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Re: speciation vs geographical variance

Post by Suckermouth »

m1ke715m wrote:i havent seen this much in catfish im speaking mostly of loricards.. i see alot of fish considered a completely different species when they look different.. is there a reason for this?
The way different hypothetical species look is the most basic way that we can differentiate species. I can't say why geographical variants of rift lake cichlids aren't separated into different species without looking more into it, but my guess is that it's a combination of not enough funding/effort/time for taxonomists to do the work or not enough evidence of differentiation between species (possibly on a genetic level). In certain other groups of animals, the subspecies is a popular way of defining geographic variants; ichthyologists tend not to like the concept.
are there hypancistrus, for example, that are the exact same that migrated elsewhere and evolved into having different stripes etc? or do they just speciate into a completely different species?
To me, when they have different stripes they are different species, because you can distinguish them. This is coupled with the fact that hybrid Hypancistrus have intermediate stripe/spot patterns as their parent species; if you don't have intermediates between two color patterns occurring in nature, this shows that one color pattern of Hypancistrus isn't mixing it up with another, and so they can be said to be different species.

I'm not sure if I answered your question.
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Re: speciation vs geographical variance

Post by m1ke715m »

not really..

in the rift lakes what happens is a part of a population of fish get seperated from the main population.. the theory is that because the water level has gone up and down over the years the shoreline has changed numerous times. most of the cichlids are bottom-oriented fishes and cannot cross deep open water to settle in another area. when they do get separated speciation can occur and they evolve into a completely different species with different physical characterstics usually adapted to their environment and how they feed (sandsifters, algae grazers, piscivores, etc) However, some fish are present in different spots and are the same species all that differs is their breeding dress.. they are "built" the same way (angle of the vomer, teeth shape, body shape, etc) and have the same breeding and feeding habits all that's different is their colors. ad konings states that(some of what i already typed is also word for word his) these species with a large amount of geographical variance were probably present in the most recent such paleo-lake rather than having evolved after the lake had risen to its current level.

im just wondering why this doesnt happen in the amazon.. maybe because they cant get seperated from the original population because theres no deep stretchs they cant cross being a river system and not a lake or maybe there are so many different hypancistrus because speciation is occuring and they evolve into a different looking fish hence the different markings.. but that doesnt explain why there are no different geographical variants of the same fish.. unless something like L-46, L-98 and L-173 are the same fish but different geographical variants of each other.. im sure there are other catfish that share this enigma as well, im just not that familiar with all of them yet.
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Re: speciation vs geographical variance

Post by Suckermouth »

The determination of species or geographical variants of the same species depends on the very human endeavor of taxonomy. If there is evidence to show these geographical variants are separate, distinguishable, and non-interbreeding, than they are separate species (in my opinion), whether or not they are currently recognized as such. If the taxonomy of cichlids isn't based on the evidence of the splits in populations, either the evidence isn't good enough yet (or there is no evidence for it), or the taxonomists haven't done it because of their opinion on what a species is. Or maybe there is some other reason, such as increasing taxonomic stability? I don't know, I'm just guessing.
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Re: speciation vs geographical variance

Post by m1ke715m »

another thought i had was maybe it has something to do with loricards being monomorphic and most cichlids from the rift lakes being dimorphic and having a breeding dress to begin with.. maybe the melanin patterns dont constitute that big of a difference in fish that can and will often turn their colors on and off due to dominance or breeding. i was thinking what you said as well maybe the entire theory is off due to the seemingly looser definition of the the word species..its just weird because some species seperate and turn into different species all together and some will just change coloring..
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Re: speciation vs geographical variance

Post by Suckermouth »

m1ke715m wrote:another thought i had was maybe it has something to do with loricards being monomorphic and most cichlids from the rift lakes being dimorphic and having a breeding dress to begin with.. maybe the melanin patterns dont constitute that big of a difference in fish that can and will often turn their colors on and off due to dominance or breeding.
It is interesting that loricariids are monomorphic, different from cichlids, but among the species that are extreme evolutionary radiations I think they are atypical. Other rapidly evolving radiations of species that are sexually dimorphic include wrasses and parrotfishes and darters. Other non-sexually dimorphic species radiations need some other sort of explanation, such as ecological explanations in the case of Darwin's finches. Also, to clarify, if I'm not mistaken, the colors of cichlids are not primarily due to melanin patterns, but to differences in other pigments.
i was thinking what you said as well maybe the entire theory is off due to the seemingly looser definition of the the word species..
Indeed.
its just weird because some species seperate and turn into different species all together and some will just change coloring..
Just changing color can be enough to qualify a species as separate. There isn't some magical characteristic a species needs to be separate from another, they just need to be separate period. Still other species, called cryptic species, are indistinguishable morphologically, but are separate species just the same based on separations evidence when you sequence their genes.
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Re: speciation vs geographical variance

Post by Bas Pels »

I think the problem relies in the question

Topic starter began about cichlids in the riftlakes, and then went on about loricarids in the Amazon river

Cichlids are very adapatable: that is, the environment in which a fish grows influences the body - much more than other types of fish. For instance, snail eating cichlids develop heavy jaws and teeth. But if one nets them, breeds them and raises the fry without snails, the jaw and teeth do not get this heavy. In fact far to light te eat snails anymore.

Therefore, scientists csan not say 'this cichlid jaw is much more heavy than that one, it is another species' because the jaw can be a reaction to the way this fish grew out.

Basically the same goes on in the amazon river.

I personally think, however, the reason another stripe in a Loricarid, or Corydoras, is used to argument another species might have to do with culture, but also with other forces. For instance, politicians don't understand the idea that a variant might evolve into a new species. If one would protect an area, basically the area needs to be specieal, and usually the specialness is defined by counting species - where unique species count more.
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Re: speciation vs geographical variance

Post by dw1305 »

Hi all,
Unfortunately I don't think we are ever going to know.

We had a similar thread a while ago, here: <http://www.planetcatfish.com/forum/view ... 7&p=235228>, which references "Molecular phylogeny of the Neoplecostominae and Hypoptopomatinae (Siluriformes: Loricariidae) using multiple genes" CA Cramer, SL Bonatto… - Molecular Phylogenetics and Evolution, (2011) <http://www.sciencedirect.com/science/ar ... 0311000030> this is well worth a read, and gives an example of an approach you could use to get nearer to the "answer".

cheers Darrel

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Re: speciation vs geographical variance

Post by Suckermouth »

Bas Pels wrote:I personally think, however, the reason another stripe in a Loricarid, or Corydoras, is used to argument another species might have to do with culture, but also with other forces. For instance, politicians don't understand the idea that a variant might evolve into a new species. If one would protect an area, basically the area needs to be specieal, and usually the specialness is defined by counting species - where unique species count more.
New species are (or should be) justified and scientific grounds, not political ones.
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Re: speciation vs geographical variance

Post by Bas Pels »

Suckermouth wrote:
Bas Pels wrote:I personally think, however, the reason another stripe in a Loricarid, or Corydoras, is used to argument another species might have to do with culture, but also with other forces. For instance, politicians don't understand the idea that a variant might evolve into a new species. If one would protect an area, basically the area needs to be specieal, and usually the specialness is defined by counting species - where unique species count more.
New species are (or should be) justified and scientific grounds, not political ones.
I fully agree, but I think in reality conversation quite often is involved. And it is easy to understand how this works
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Re: speciation vs geographical variance

Post by racoll »

Great thread. Very interesting! I apologise in advance for some of the jargon!
m1ke715m wrote:so anyone that keeps africans knows that alot of fish are the same species but different geographical variants where only the colors and depth found are different.
As you probably know, there's no agreement as how to define a species. This has arisen due to the confusion of pattern (what's observed), versus process (what causes the patterns). Recently most biologists have accepted that species are generally conceptualised as simply "unique, independently evolving entities". How you provide evidence for these entities is up to the scientist, but should be grounded in appropriate theory. So, this gives a lot of leeway, and in effect depending on what kind of data you use, and your philosophy, one man's geographical population could easily be another man's species.

It's also important to also note that species are not formed "overnight". For some that we observe (e.g. many cichlids) there is a period of incipient speciation, where they are two diverging populations, not entirely distinct yet. There may be ongoing gene flow, or they have only differentiated very recently and few differences can be observed. These cases will always be difficult to classify in a nomenclatural system.
m1ke715m wrote:most of the cichlids are bottom-oriented fishes and cannot cross deep open water to settle in another area. when they do get separated speciation can occur and they evolve into a completely different species with different physical characterstics usually adapted to their environment and how they feed (sandsifters, algae grazers, piscivores, etc) However, some fish are present in different spots and are the same species all that differs is their breeding dress
m1ke715m wrote:im just wondering why this doesnt happen in the amazon ... but that doesnt explain why there are no different geographical variants of the same fish
Surely it does, and there certainly are! See Farias and Hrbek (2008) for an example using discus. The difference being in the amount of effort that has gone into studying the two regions.

The Rift Lake cichlid fauna has had a huge financial investment in scientific effort, and have been studied for many years as a model of evolutionary theory. Just pick up any textbook or type "cichlid evolution" into Google Scholar. The system is relatively easy to study. We've kept the cichlids in tanks and dived into the lakes to observe behaviour, we've collected huge numbers of specimens, we've sequenced their genes and now genomes, and numerous books have been written. By comparison, we know next to nothing about the fishes of the Amazon basin. For one thing it's huge (7 million km2), with a fish diversity orders of magnitude larger than the Rift Lakes. It's a daunting task, and currently we only have a very rough idea of what's out there. Take the loricariids and Corydoras; the aquarium trade is finding them faster than scientists can describe them, at probably a 25:1 ratio!

The main point being though, that you just can't compare the difference in effort. As an example, I'm sure genera like Apistogramma will be every bit as interesting as the Rift Lake cichlids, but as far as I know there's not a single person seriously working on them, compared to say a dozen entire laboratories working on Rifts.

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Re: speciation vs geographical variance

Post by m1ke715m »

what about L-333 and its different "color forms"
http://www.planetcatfish.com/forum/view ... 13&t=35193

same fish? different geographical variant or different species? and how come its referred to as L-333 for this fish but other fish with differences in line width or color are different species.. im kinda playing devil's advocate here.. just poking all your brains
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Re: speciation vs geographical variance

Post by racoll »

m1ke715m wrote:what about L-333 and its different "color forms" same fish? different geographical variant or different species?
Well, first off, you'd want an experienced morphologist to look at the fish, and try and pick out consistent differences among the populations. If this was not successful, and you were still convinced that they're different, then move onto a crude molecular analysis using mtDNA, and if that failed, then a genome-wide SNP scan would be the best option. If there was still nothing telling them apart at this stage, then your null hypothesis that the groups are the same cannot be rejected.

P.S. I reckon about 80% of the "L333" posted on the forum are not that L number!

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Re: speciation vs geographical variance

Post by Jools »

racoll wrote:P.S. I reckon about 80% of the "L333" posted on the forum are not that L number!
I cannot agree more.

Jools

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Re: speciation vs geographical variance

Post by Mike_Noren »

Geographical "races" in fish are nearly all un-named species.

A species is any group of organisms who have embarked on their own evolutionary trajectory, i.e. are separate from all other groups of organisms. Usually, but not always, this separation is caused by geographical separation. Close in time to the separation, species like this can be 100% identical to other species in every respect, and if isolation is lifted it may merge with other species again.

For us to recognize that something is a species, a group of organisms have to be distinguishable from all other groups, they have to have a diagnostic trait, a unique character or set of characters which can be used as a proxy to identify reproductive isolation. (Note that a character which does not indicate reproductive isolation is not diagnostic, e.g. "albino" is not a species). When we recognize that a group of animals is a species, we name it - due to tradition and convention a binomial name in Latin - to allow us to unambiguously refer to the group.

This species concept is both reasonably stringent and operational, and is almost universally accepted in ichthyology^1.

Victoria and Malawi cichlids are awkward. These groups of fishes have diverged on their own unique evolutionary trajectories very recently in time, in some cases just a few thousand years ago, and are still very close in morphology and genetics. Compounding the problem is that they differ from each other mostly in color, and color changes with age, sex, and mood, plus mostly disappears after death. This makes classifying based on color difficult, and historically color was largely ignored in ichthyology.
Also their sheer numbers are daunting to many researchers, who balk at having different species at every rocky outcrop of Lake Malawi.

Nonetheless, from an operational classification point of view it's pretty straight-forward: do the "morphs", "forms", "races", "subspecies" or whatever one call the groups, have any diagnostic traits or combination of traits which allow separating them from all other? If so, they're species and should be named; if not, there is no reason to keep them separate from the other at all.


^1: Not, however, in some other fields. Especially herpetology and mammalogy seem to have a tradition to lump diagnosable species for subjective reasons. E.g. biologically speaking "tiger" is clearly five different species, with different size, patterning, biology, distribution, and conservation status, but mammalogists have decided to lump them under one name "to not confuse the public", and in herpetology there are bizarre situations like this.
-- Disclaimer: All I write is strictly my personal and frequently uninformed opinion, I do not speak for the Swedish Museum of Natural History or FishBase! --

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Re: speciation vs geographical variance

Post by racoll »

Fantastic explanation Mike!
Especially herpetology and mammalogy seem to have a tradition to lump diagnosable species for subjective reasons
It's odd how different fields approach essentially the same problem in different ways. In birds for example, there's a tendency to oversplit taxa based on really minor variation/gradation in plumage, which often does not effectively diagnose reproductively isolated groups. They also seem very keen on the rank of subspecies, which fortunately, ichthyologists avoid like the plague.

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