a post came up the other day in the id forum for a catfish.
it looked like other genus Icatalurus punctatus but is tagged as a Ameriurus catus white catfish and this fish looks nothing like other Ameriurus at all. how does this happen?

you might enjoy the link below -- excellent synopsis. More recent DNA work has generally supported Lundberg's hypotheses.

http://books.google....talurus&f=false

That's an excellent question, Tony. I'm not a taxonomist, but I'll do my best to answer it.

In tthe old days, species were grouped into genera based on overall similarity and shared characters. Which characters were important was determined by the scientists studying that group, largely by intuition since there was not theory behind the groupings. That all changed when Darwin, Wallace, and their followers showed that similarities between different species are due to those species having a common ancestor. The new, evolutionary taxonomy places species into genera if those species all share a common ancestor, and no other species is descended from that ancestor; a group like this (all the descendants of a single ancestor) is called a monophyletic group. Taxonomists look for shared-derived characters, or synapomorphies, to determine if a group is monophyletic. For example, fur and mammary glands are synapomorphies of the Mammalia.

The catfish species now placed in the genera Ameiurus and Ictalurus are very similar. For many years they were treated as belonging to a single genus; the name Ictalurus was used because it is older than Ameiurus and therefore has precedence. However, a closer look at these catfishes and their relatives revealed that the characters that made the fork-tailed cats and bullheads similar were not shared-derived characters, but primitive characters! The bullhead/white cat group share a more recent common ancestor with the madtoms, flatheads, and some oddbal cave catfish than with the fork-tailed cats. The taxonomists were now faced with a decision: in order to render the catfish genera monophyletic they could either: 1), drop the fork-tails, bullheads, white cats, madtoms, flatheads, and cave-dwelling cats into a single genus, or 2) split up Ictalurus. Either would be an acceptable decision by the "rules" of nomenclature, but the second option was thought to be be more informative.

So why is the white catfish an Ameiurus and not an Ictalurus? Its moderately forked tail does resemble that of an Ictalurus, but this is not a shared-derived character. Other aspects of its morphology and genetics show it to be a perfectly good bullhead that just happens to have a forked tail.

*EDIT* Ha, I'm too slow!

*EDIT* Ha, I'm too slow!

So you put more time into a well thought-out reply... that's certainly not a bad thing! I'm a bit tired from hauling a ponar dredge all day, and took the lazy way out!

So you put more time into a well thought-out reply... that's certainly not a bad thing! I'm a bit tired from hauling a ponar dredge all day, and took the lazy way out!

I agree. A great summation. Well-done!

That's an excellent question, Tony. I'm not a taxonomist, but I'll do my best to answer it.

In tthe old days, species were grouped into genera based on overall similarity and shared characters. Which characters were important was determined by the scientists studying that group, largely by intuition since there was not theory behind the groupings. That all changed when Darwin, Wallace, and their followers showed that similarities between different species are due to those species having a common ancestor. The new, evolutionary taxonomy places species into genera if those species all share a common ancestor, and no other species is descended from that ancestor; a group like this (all the descendants of a single ancestor) is called a monophyletic group. Taxonomists look for shared-derived characters, or synapomorphies, to determine if a group is monophyletic. For example, fur and mammary glands are synapomorphies of the Mammalia.

The catfish species now placed in the genera Ameiurus and Ictalurus are very similar. For many years they were treated as belonging to a single genus; the name Ictalurus was used because it is older than Ameiurus and therefore has precedence. However, a closer look at these catfishes and their relatives revealed that the characters that made the fork-tailed cats and bullheads similar were not shared-derived characters, but primitive characters! The bullhead/white cat group share a more recent common ancestor with the madtoms, flatheads, and some oddbal cave catfish than with the fork-tailed cats. The taxonomists were now faced with a decision: in order to render the catfish genera monophyletic they could either: 1), drop the fork-tails, bullheads, white cats, madtoms, flatheads, and cave-dwelling cats into a single genus, or 2) split up Ictalurus. Either would be an acceptable decision by the "rules" of nomenclature, but the second option was thought to be be more informative.

So why is the white catfish an Ameiurus and not an Ictalurus? Its moderately forked tail does resemble that of an Ictalurus, but this is not a shared-derived character. Other aspects of its morphology and genetics show it to be a perfectly good bullhead that just happens to have a forked tail.

*EDIT* Ha, I'm too slow!

Nathan,
thank you! for taking the time to respond in your own words.
you and Todd C,Brian Z, have away of saying/wording the same things i have read but somehow it just makes more sense.

Edited by CATfishTONY, 12 August 2010 - 05:02 PM.

Glad I could help, Tony. By the way, Dave and Tom are taxonomists- so if you have tough taxonomy questions, they're the ones to ask!

I see that Lundberg's family tree of Ictaluridae puts the Flathead catfish (Pylodictis) as the closest living relative to Satan. I heartly agree. Now there's some poetic justice.

Gerald (in eastern NC where the flathead is a very nasty invasive exotic)

you might enjoy the link below -- excellent synopsis. More recent DNA work has generally supported Lundberg's hypotheses.

http://books.google....talurus&f=false

you might enjoy the link below -- excellent synopsis. More recent DNA work has generally supported Lundberg's hypotheses.

http://books.google....talurus&f=false

Thank you for the link Dave,
it took some time to read and will take longer to understand for sure.