Superorganisms = organism

People like to talk about ants as ‘superorganisms’. Of course, we’re all kind of superorganisms, built out of a structure of captured cells and using home-grown bacteria to function. But when we talk about ants, wasps, and termites, we mean something else. Each insect on its own seems to be an independent organism – though they can’t all survive away from the colony – but in reality, the colony is the organism.

In PNAS, Hou et al. apply the metabolic scaling law to eusocial insect colonies. Individual organisms have a metabolic rate that scales as the 3/4 power of body mass. Along with this are laws scaling reproductive organ mass, total biomass, and organism (colony) growth with metabolism. Individual ants do not follow this law: worker ants have almost no reproductive organs while the queen has tons of ’em.

The figure above shows the body mass vs. metabolic rate for some (non-ant/wasp/termite) insects and for various colonies as a whole. And the curves are the same! If you look at the other predictions, they all turn up exactly on the curve, too. So it is only when you consider the colony as a whole that eusocial insect act as a proper organism. Iain Couzin once mentioned to me that ants in a colony act analogously to neurons in a brain, though I can’t for the life of me remember how that was. But see, the individual ant is just like a lonely neuron: meaningless.

Ants ants ants

Man I’m behind on my ant blogging. OK, here’s what I’ve learned recently, thanks to Science. Why does Science have so many more ant articles than Nature? It’s quite an unfortunate oversight.

To start things off, we have a fascinating bit of research about dancing lizards. See, fire ants like to ants1eat some nice hearty meals, like lizards. They surround the lizard, pry up the scales, and inject venom. To combat them, some lizards have discovered that they can give some hearty shakes and wiggles, and throw the ants off. Lizards who live longer around fire ants are more likely to do this (and also have sturdier hind legs!). So then – is this a genetic influence? Or a lizard cultural one?

Now let’s turn to the ant queens. In order to cement their social status, ant queens give off a squeal that elicits increased benevolence from their workers. This is in addition to the normal communication signals of “semiochemicals” (ie, pheremones). Some insects have been known to infiltrate ants society by mimicking their semiochemicals. After all, if your only identification method is chemicals, it’s easy to get tricked. But even worse, these other insects have learned to mimic the sounds made by queens so they are instantly treated as royalty – even their pupae are given the royal treatment. Apparently, vocal signals are only used to signify caste status, so if you’ve got a good voice, you can be anyone in society that you want to be.

Next up is an article questioning how ant eusociality (ie, being a superorganism) evolved. How exactly does an insect become caste-like? The consensus in the field has long been that it is because of altruism to kin – ants will be sterile in order for the queen ant to pass on some portion of their genes. Intergroup competition leads to this being a successful strategy. But recent findings contradict that theory. Among other evidence, some bees that are social come in pairs: one bullies the other to become a worker while the first becomes the queen. As time goes on, it is the kin least related to the queen that stay and the more related kin that leave. The most important bit here is an evolved behavior to stay near a nest. Of course, the vast majority of the field still disagrees but there ya go, that’s E.O. Wilson’s opinion.

ants2The final bit is less about ants and more about general evolution. A paper in science is attempting to show that evolution is less random than it might appear at first glance, and that its direction can be almost predictable. Their first bit of evidence is convergent evolution – how vastly different species can evolve behaviors or appearances that are nearly identical (homologous) – or even parallel evolution – when different species evolve the same gene in parallel. But these parallel evolutions often act on the same gene, even when there may be eighty or more genes that could mutate to do the same thing. Why? The authors suggest the kinetics and chemistry of the transcription factors and signaling molecules – the “genetic network” – constrain evolution in such a way that only a few genes are at all likely to be targeted for evolution. They give plenty of examples of how evolution is constrained and explore their hypothesis that evolution is predictable – it’s interesting and definitely worth a quick read.

Finally, a series of videos of trap jaw ants. Their mandibles are so powerful that they hurl themselves in the air when they close. Sweet.