Celsus

Hi all,

So I just came across this article which says that insects may have had polyphyletic origins. Helpfully, all the links below the article have nothing to do with the topic, and it's from the ever-reliable Pravda. A Google and PNAS search turned up nothing useful. Does anyone have any information confirming or refuting this?

Cheers,
Joel

theyeti

Here's a better article:

http://www.lbl.gov/Science-Articles/...e-of-life.html

It's not that insects have polyphyletic origins, but that one group previously thought to be nested within the insects -- the collembolans -- is actually an outgroup whose branching predates the common ancestor of insects and crustaceans. (edited to add: whoops, it appears instead that they were thought to be a sister group to the insects, and not nested within them. This study indicates that they are not a sister taxon, and instead share a common ancestor which predates the insect/crustacean split.) Hence, their six legs and other similar characters are an example of convergent evolution.

As far as I can tell, there is no reason to doubt the monophyly of the rest of the insects.

theyeti

Wounded King

The reference is

Nardi F, Spinsanti G, Boore JL, Carapelli A, Dallai R, Frati F.
Hexapod origins: monophyletic or paraphyletic?
Science. 2003 Mar 21;299(5614):1887-9.

The paper looks quite good, it certainly isnt saying anything vastly iconoclastic. I dont feel my world view would be particularly shaken by a polyphyletic origin of hexapoda, but then Im not an enotmologist.

theyeti

One other thing I should add: The fact that the branchings here are going back a good 500 million years give or take makes me skeptical that mtDNA is a good phylogenetic tool in this case. Of course I assume that their methodology was carefully reviewed since this is being published in Science.

theyeti

Celsus

Ok, thanks for the articles! As you might have guessed, I wanted to add that whatchamacallit to the "What Kind is It?" thread, since it's not a member of the Hexapoda. I just needed some proper confirmation since all I could find was that Pravda article.

Non-praying Mantis

Interesting!

Collembola were one of my favorite orders of "insects," but maybe now I shouldn't call them that.

Collembola were/are classified as hexapoda, because they have six legs, but they don't just have six walking legs. In addition, they have a pair of "springing legs" that give them the name springtails. These "springing legs" are attached to the rear of the abdomen, and they fold underneath it. There is also a small clasper that grabs the springing legs and holds them in place.

Collembola are quite common in leaf litter and you can easily find them using a collection technique called a Burlese funnel: a large funnel is used to collect organisms that fall from leaf litter placed under a light bulb (which heats the litter), and on top of a screen. The funnel ends with a jar of alcohol to preserve what falls down.

I was aware of the "controversy" between a mono- and paraphyletic origin of arthropods, but not insects. Certainly, crustaceans and insects share a common arthropod ancestor, but perhaps arachnids and horseshoe crabs do not. Current thinking also gives the centipedes and millepedes (and other myriapods) a common ancestor, which they perhaps share with insects and crustaceans.

NPM