Our need for science

[Innesfan]

I'm with anewbie, so many new names now than even many years ago. Better info or better IDs. DNA?

In many cases, DNA is challenging our understanding of what a species is. I am told that in Nannostomus, for example, there is more DNA variation among populations of N. beckfordi than there is between N. beckfordi and some other Nannostomus species. Some Apisto veterans have told me this is true in that genus as well. In Carnegiella, "Hatchetfish" there are 'crytpic species' of N. marthae and others. They are identical to each other to the naked eye, share the same waters in some instances, but do not share the same dna genotype and are reproductively isolated. Both are passed on to us as N. marthae but they are two distinct species, as we define what a species is.

Similarly in Symphysodon, "Discus," two recent, near simultaneous revisions both found there were three species in the genus but came up with different descriptions and names for what those species were. Two of the species will 'hybridize' both in nature and in captivity. The third, S. tarzoo, "the Green Discus," will not. The revision that I found the more sound included this observation: "A molecular study found five main groups, which generally matched previously recognized phenotyoes. They recognized them as evolutionarily significant units and species."

"Evolutionarily significant units" -- I find this interesting and perhaps a better way to understand and reflect that evolution is an active process and our past efforts to identify species may need to be rethought.

 

[GaryE]

"Evolutionarily significant units" -- I find this interesting and perhaps a better way to understand and reflect that evolution is an active process and our past efforts to identify species may need to be rethought.

I think we started out with religious world views of species - distinct created entities, unchanging. That's gone, but the old way of thinking isn't. It's affected what people were looking for, and creates a conflict in what we expect.
Defining species as a concept is hard. I like the vision of an evolutionarily significant unit. The things you're describing are well known in the killifish world, where species can be identical to the limited human eye, but different in their DNA, and unable to breed together. For hobbyists, this created our insistence (with killies) of keeping the capture location attached to the name. The fact that two fish from different places look the same may be a failing of our eyes and brains, and not a reflection of what they are. If the two streams they're in have been apart for a few thousand years, or more, or less, they may have diverged and we could create infertile mule hybrids. Many a line of killies has probably been lost to that.
We can redefine the word species, but such things exist. It's the borders that are hard to see.
For the hobby, most aquarists will ignore these debates, as the stuff of science nerds. They mainly affect breeders, and list making collectors.
Names can be science. A rummy nose tetra is a commodity, but in the scientific sense, it's several evolutionarily significant units (species) that can be hard for new fishkeepers to distinguish. Trigonostigma (rasboras) of the harlequin type, Rubicatochromis jewel cichlids, Aphyosemion australe killies - there are a lot of things we can spot even in this little hobby.
It gives us something to think about when we're on the bus.

 

[gwand]

There is even a qualitative aspect to the seemingly quantitative technique of whole genome sequencing. The investigator decides when two DNA sequences are similar enough between two fishes to declare them the same or separate species. This is a somewhat arbitrary decision. I opine for the good ole days when two animals were considered the same species if they produced fertile offspring.

 

[GaryE]

The taxonomists I've spoken with aren't deciding through the DNA, but seeing if the DNA supports the conclusions they've come up with using the older anatomical methods, as well as the cross breeding 'tests'. Or so it seems to me, in my non scientist's understanding.

 

[gwand]

We want a binary answer: yes, it is the same species; no, it is not the same species. However at end of the day, it is still an arbitrary process with agreement based on the necessity to reach a decision. Something we just have to live with. Maybe species is a man made artifact.

 

[Innesfan]

I opine for the good ole days when two animals were considered the same species if they produced fertile offspring.

Oh, I hear you. One of many reasons why I find the Discus revision so interesting. 'Blues,' 'Browns' and 'Heckels'--two species comprising three phenotypes and three 'evolutionarily signifcant units'--will all 'hybridize' and produce fertile offspring. "Greens," S. tarzoo, will not.

And as far as 'species' being a man-made artifact, IMO, it most certainly is. Interesting and fitting that you use the word 'binary.' Linnaeus created a perfectly user-friendly binary nomenclature system for us so that we are able to identify and communicate about what we are calling species. But over time we are learning that Nature has a far more intricate and nuanced story to tell.