What is a species?

New cichlid species and taxonomy
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DRE
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What is a species?

Post by DRE » Mon May 02, 2016 11:19 pm

We had an interesting discussion in a facebook group about the question: What is a species?

There were some who rather strongly claimed that there is only one valid definition: "species are defined as populations that can interbreed and produce fertile offsprings".But since they also realised that many cichlid species easily interbreed they added this: " and will interbreed in a _free choice_ environment."

As far as I have understood, hardly no description of new species today validate if they can inbreed and if their offspring is fertile. Instead certain morphological traits are compared and if there are clusters of differences they are seen as different species. Or DNA analysis is used and then also here clusters of differences separated from each other can be used to separate species. Well in some level of layman terms this is the way I've understood it.

I guess there is some correlation between these two definitions since they look different because they and not inbreeding frequently.

So my question, what is really the definition of a species.I guess there are some rules ichthyologists need to comply to to define a new species for it to be valid.
Discovery consists of looking at the same thing as everyone else and thinking something different

Bas Pels
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Re: What is a species?

Post by Bas Pels » Tue May 03, 2016 1:34 am

As far as I know, the scientific community does not agree on any definition of what a species is. Some scolars can be using one definition, while others use another.

The problem is, in mammals hybrids are most often not fertile, and thus the fertility thing feels natural in a species definition. But in fish matters are different. We have in Central America Parachromis dovii, feeding on Hypsophrysis nematotus, while both species can interbreed through a number of species in between. Still that does not make the P dovii canibals.

I myself think the thing is, animals live in populations. That is groups which interbreed, and each population can be seen as a genetic pool. The problem is, obviously, storms can take fish from one population and bring them to another. Or change the coarse of rivers, connecting populations which have been seperated for ages.

Species is something we humans have invented, because the real world is basically too complex to really understand. But others feel differently.

However, as I am certain species do not exist, I reailize providing a devinition will not Always be easy

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DRE
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Re: What is a species?

Post by DRE » Tue May 03, 2016 11:42 pm

Yes I understand that there is a complex question. Still we have peer reviewed scientific papers defining species. These papers obviously are accepted and thus there are a set of methods that are approved. I don't think I have seen any paper using the inbred->infertility hypothesis in their paper. Instead it seems accepted to look at morphological differences as well as DNA differences.

If I would write a paper claiming I have found a new species just based on that it lives in another river than another I'm sure it would not be accepted.

Thus there are some accepted methods to differentiate a species from another. If these are unwritten rules it is fine, they still exist.
Discovery consists of looking at the same thing as everyone else and thinking something different

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SergeS
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Re: What is a species?

Post by SergeS » Wed May 04, 2016 7:41 am

I just ran across this as well recently after I read something about a sub-species in Lake Malawi. Don't remember which one it was, but that doesn't matter. As I had some doubt, I looked up the exact definition of a species and concluded that - based on the "dictionary definition" - Lake Malawi only has one endemic species, which could have about a 800 sub-species and even more geographical varieties. After all, they can (and will) all breed, ánd produce fertile offspring. Also: there are reports that large Malawi predatory cichlids and Mbuna breed as well, if the circumstances are right (wrong is the better word here I guess), so I can see where the "freely chosen environment" idea comes from. Regardless, the "dictionary definition" of a species does not look right to me.

I am not sure if we (mankind) will ever be able to come up with a solid definition or even a set of rules. It will always be too broad or too narrow, depending on what you want to describe. So even trying to define a set of rules, one that applies to all taxa, would be as good as impossible. And otherwise it would cause a massive earthslide in certain taxa :)

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DRE
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Re: What is a species?

Post by DRE » Wed May 04, 2016 8:09 am

That would mean that all currently peer reviewed and appeoved descriptions of Malawi cichlids are all wrong?
Discovery consists of looking at the same thing as everyone else and thinking something different

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SergeS
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Re: What is a species?

Post by SergeS » Fri May 06, 2016 2:45 am

Yes, if the definition of "a species" involves that two animals are only of a different species if they can not produce fertile offspring, that's exactly what it would mean, I guess. But I don't think that any scientist involved in (the determination of) cichlids agrees with that part of the definition of what a species is :)

Paulo José Alves
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Re: What is a species?

Post by Paulo José Alves » Wed May 11, 2016 7:28 am

Hi

I´m pretty sure that within 10 or 20 years the actual Linnean definition of species will be abandoned and the current taxonomic classifications will be abandoned as being invalid.
Nowadays each taxonomist has his own opinion and a new classification is just that, an opinion. Everybody follows it as it was the gospel but it really isn´t. Some years along the line someone will make a change, discover a fault, new data, etc and comes up with a new classification.It happens so often that it has becoming tiring to cope with all the constant changes in aquarium fish names. No to speak of the super-delirious splitist stance of today´s taxonomists, everything, the smalest difference, is enough to justify erecting a new species even if it is almost the same thing as the fish next door.
All this just leads in my opinion to the lack of credibility of taxonomy.
All The Best
Paulo José

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