Ready to rock.

My colleague Corrie S. Moreau, Assistant Curator at the Field Museum of Natural History in Chicago, got interviewed by ScienceWatch.com in occasion of her highly cited paper in Science published back in 2006.

It’s a nice interview, but I have a couple of reservations though. She states that:

This well-resolved phylogeny reinforced some previous hypotheses about the morphological evolution of the ants, but we also were able to demonstrate that the modification or reduction of the stinger happened twice independently within the ants.

By twice she refers to subfamilies Dolichoderinae and Formicinae which, true they are characterized by extensive reduction and disarticulation of the sting apparatus or complete disappearance of it respectively, so that the finding that they are not sister groups entails that loss of sting ocurred independently in the common ancestor of each clade. But there are various other parts of the ant tree where the sting is reduced and useless as a weapon, so this was known to happen more than twice even before molecular phylogenies were out. Think the army ant Dorylus and the myrmicine genus Cephalotes (turtle ants) just to name a couple of examples.

The other is Cories’ reply to the question:

Do you foresee any social or political implications for your research?

Because here I was really, really hoping that instead of her actual answer she would had said something like “Biological weapons of course! Just think of the Alien series of movies.”

Hypognathus condition in insects (left image from Wikimedia commons; right drawing modified after Snodgrass 1935)

In most insects, and certainly in all bees and most wasps, the mouthparts hang at the bottom of the head and, since each set of mouth pieces derives from a particular segment along the main axis of the body, they are positioned one after the other in a sequence from front to back: labrum¹; mandibles, maxillae, and labium. This head arrangement is known as the hypognathous condition, and can be considered the groundplan for insects.

In hypognathous insects the very first pair of appendages at the front of the head are the antennae, quite important since they are the primary tactile and smelling organs, so this makes sense (no pun intended).

Prognathus condition in insects (left image modified from ©Alex Wild; right drawing modified after Snodgrass 1935)

In ants, however, the very first thing at the front of the head are the mounthparts. Usually the large mandibles of these insects are at the forefront. But the term prognathy here (that is, “projecting jaws”) is really describing a functional condition that results from a significant structural rearrangement of the ant head: the entire head capsule is tilted almost 90 degrees forward, so what used to be the anterior region in a hypognathous insect is now the upper part of the head, and what used to be the bottom (the mouth) is now the front-most region.

In prognathous insects the antennae are no longer anterior in the head but are attached dorsally, and the different mouth pieces no longer run from front to back but are arranged from up to bottom (in a dorso-ventral axis). In fact, in relation to the rest of the elements in the head the mouthparts have not changed position. There is one important exception to this– the place where the head attaches to the neck and which has the hole by which the digestive tube, neural cord and the rest of the entrails go through has shifted from its ancestral place opposite to the antennal sockets to the upper back of the head, opposite to the mouth.

One way to envision this major structural rearrangement with more familiar examples is to compare the head of your cat or dog with your own head. Look at the head of your pet (even your goldfish will do). If you trace an imaginary line that passes right between the eyes (imaginary is the keyword here), that line will exit at the back of the head right through the hole that connects the head with the neck, the hole through which the neural cord coming from the brain passes (the foramen magnum in anatomical speech). Assuming your pet is standing straight in four legs, this imaginary line will continue parallel to the vertebral column all the way to the end and exit at the rear (the anatomical name of which I will spare for you). Now perform the same for your own head. In your case the imaginary line that went in-between your eyes will find a dead end at the back of your skull, right above the nape. In us, the “back” hole of the skull is located at the floor of the head. What happened is that as humans evolved up-rightness, the foramen magnum shifted position from back to bottom to balance our big heads and keep our faces looking to the front. This is also why if we lay chest down we look utterly ridiculous with our faces kissing the floor (or risk torticolis), as opposed to our cat or dog which will be graciously resting in front of the fireplace face-straight. Well, from wasps-like ancestors to ants the insect foramen magnum shifted exactly in the opposite way.

Now, in us jawed vertebrates (you and your pets) none of these conditions are called prognathous. This term has a very different meaning and refers to cases where either the upper jaw projects beyond the lower jaw or vice versa, something that can be appreciated in certain dog breeds like the Pug and in people that have subject themselves to large quantities of anabolic steroids, like certain current Governor of California.

Rhytidoponera metallica (April Nobile http://www.antweb.org/)

Back to insects, I have heard entomologists deny that prognathy is a diagnostic feature of ants, a synapomorphy. It is true that in some ants their mandibles seem to point downward, but this is just because having the neck attachment way in the upper back does provides the head articulation with a wider range of play. Again, the important point is not in which direction do the mouthparts project, but where is the location of the foramen magnum within the insect head.

Detach head of a Figitidae wasp (Via Mattias Forshage http://www.morphbank.net/)

Case in point. If you want to take a SEM of the base of the mouthparts in a regular wasps, the first thing you are forced to do is to detach the head from the body and place it face-down into the mounting stub. Your SEM will nicely show both the mouthparts and the foramen magnum.

Underside of head of a worker of Cerapachys nitidulus (Scanning Electron Micrograph, Roberto Keller/AMNH)

I have taken hundreds of SEMs of ant mouthparts and I never had to detach the head. The only thing you need to do is flip the ant, legs up, and you will have a unobstructed view of the base of the mouthparts. You won’t be able to see the foramen magnum in the same image though!

Notes and references

Yes, the discrete logo appeared at the front of each research article.

The articles may have been long, descriptive and rather dull (although important), but boy did they made up for it with crazy typography in the journal’s logo!

Finger puppet!

I agree with her, preparing animals that have the skeleton on the outside is way easier and much more cleaner.

In the past couple of days I have been doing some background literature research on the topic of insect walking. What I did not know is how big this field is compared to other topics in entomology. The reason behind this popularity is, unsurprisingly, the fact that the results of such research have a direct technological application: robotics. In particular six legged robots or hexabots (they should be called something like hexapodbots, but I guess the shorter name is cooler).

There are simple good reasons to go for six legs if you want to design a walking apparatus. Think on how many times when you go to sit down at the coffee shop you spend the first couple of minutes folding whatever piece of paper or cardboard you find around in order to place it underneath one of the legs to stop the four-legged table from wobbling. But you never had to do that for three-legged tables. That is because three legs are just the right number to stop whatever they support on top from moving in any dimension. Take one leg out and your table will fall following a straight arch path. Add one leg and your now four-legged table has usually more than one way to rest on three supporting points. Three legs is the most stable arrangement.

OK, but why six legs then? Because with that number you can always leave three legs firmly on the ground while you move the other three, which makes for a very stable walking. One in which the body can be kept at the same height plane while traveling forward, something insects do most of the time while walking.

Most of the research on insect walking uses stick insects and cockroaches as test subjects, and involves putting the animals to walk on treadmills to observe the pattern of leg movement under different conditions of speed, inclination, etc and, for example, immobilizing (our cutting) one or more legs to see how the movements are adjusted. A big part also involves figuring out the nervous circuitry responsible for coordinating all those legs.

I have to say, it is all fascinating and cool, but it is useless cool for what I am interested in that is, you guessed, leg anatomy and simple biomechanics (what muscle moves which skeletal piece). At the end I realized that going back to basic comparative anatomy is all I need for now. And for that Robert E. Snodgrass never fails me.

Don’t expect this blog to pick up in speed anytime soon though, but I’ll keep you entertained from time to time dear readers.

Now, the fact that the registration fee includes ethanol and ethyl acetate (for preserving the locally collected fauna) should tell you something about the level of geekiness of the crown that normally attends these meetings. But, it’s professional geekiness mind you.

You can find more information here (pdf).

Now Beccaloni provides further evidence to back his opinion in the form of a letter written by Wallace to Walter Bates in 1846. Read for yourself and decide.

Oh, and a happy new year to all the readers of this blog!

This is my reply to the nice image by myrmecos.

The meeting is organized by young researches, and this year will be specially interesting because there will be a discussion about creating a national society of evolutionary biologists.

I will be talking about the evolution of mouthparts within ants, covering some fascinating new discoveries that I haven’t share here yet but will blog about some time in the near future. In the mean time, here are a couple of my slides.

Media sources: antweb.org; Roberto Keller/AMNH.

Media sources: Wiki Commons; Alex Wild (http://www.alexanderwild.com/); R.E. Snodgrass 1935.

E. Haeckel

You may not fancy public humiliation of scientific papers (ah come on, who doesn’t?), but the Pewter Leprechaun Awards Ceremony is a fun read. If you want to know what is this all about look here.

You really need to know well your history on systematics and biogeography to fully enjoy the piece, but if you don’t you will do well in putting Google to a good use and run some searches on those names. On a side note, I do think Brazeau’s paper didn’t deserved the nomination, specially among the other contestants.

I hope they do send a pewter leprechaun to the winner (and blog about it).