How a Common Beetle May Offer Deep Insights Into Evolution

When Joseph Parker was growing up in Swansea, in South Wales, he had an obsession with insects. His room was filled with tropical insects, but he discovered a common local one that really captured his attention. The rove beetle.

The tiny beetles are everywhere, but most interestingly, in ant and termite colonies, where they evolved to live as social parasites, mimicking the ants in body shape and producing chemicals that in some cases even convince the ants to feed them. In other cases they prey on ant young and steal food, all the while masquerading as colony members.

Most remarkably, many lineages have independently evolved the same changes in body shape and chemical gland functioning, making them rich turn for pursuing deep questions about physical and behavioral evolution.

Last fall, Dr. Parker, who recently set up a lab at CalTech devoted to using rove beetles, reported in Biorxiv how a flexible abdomen and chemical-producing gland could be pre-adaptations, in that they are easily modified by genetic change to make the beetles look more like ants and produce chemicals that identify them as ants.

It is rare that a new organism is introduced as a model for study in biology, but Dr. Parker thinks rove beetles have the potential to answer questions about evolution that other insects, like the ubiquitous fruit fly, Drosophila melanogaster, do not.

“As valuable as knowing everything about Drosophila is, it’s not the whole universe,” he said.

Excerpts of a telephone conversation with Dr. Parker are below, edited for clarity and length.

Q. How old were you when rove beetles became your passion?

A: Seven years old was when I started. All of the rest of the world fell away and it was just me and insects. Growing up in the U.K., we don’t really have big, flashy insects, so you end up collecting what you find around you and that’s often quite small beetles that live in dirt and a lot of those are rove beetles.

One of the first things you learn about rove beetles is that they have this amazing evolutionary tendency to become symbiotic inside ant colonies. And when they do this, their behavior and their anatomy change, and they become what we call social parasites. These are intruder organisms that are able to bypass or kind of hijack ant nest mate recognition systems and integrate socially into the organization of ant colonies and they do this to termites as well.

Q. So you stuck with the rove beetles?

A. They’re a fascinating group of organisms for studying how interactions between different species can evolve because they’ve been able to do it so many times during their evolutionary history. They’re able to socially interact with ants and they are able to produce chemicals that can manipulate ant behavior, so they can integrate into the fabric of ant society.

Q: This has happened independently in many lineages of rove beetles. How?

A: There’s clearly something special about these beetles compared to almost all other groups of arthropod and really all other forms of animal life that predisposes them evolutionarily to be able to do this.

This is a fascinating group of organisms and I’ve essentially dedicated my life to studying them. I actually trained as a fruit fly geneticist so I could gain molecular biology and developmental biology expertise, so that I could then apply that to rove beetles.

During the past few years, that’s what I’ve done, applying modern tools of molecular biology and genetics to rove beetles to understand the evolutionary basis for this form of symbiosis that they’ve evolved so, so many times.

Q. Why is this social parasitism such a good way to live?

A. The payoff for being able to become a symbiont inside an ant colony is very big. If you can get your foot in the door of an ant colony, there are no other predators, it’s climatically controlled, it’s full of resources. You can feed on the ant brood and the food that the ants have harvested to your heart’s content. And if you’re really clever, you can trick the ants into feeding you directly, mouth-to-mouth.

They’ve really broken the code of nest mate recognition, and their whole life history adapts to being able to coexist with ants and integrate socially into colonies of ants. The beetle larvae have their own chemical to ensure that they’re, in some cases, fed preferentially over the ants’ own larvae.

Q. Is this one common ancestor that becomes a parasite giving rise to all sorts of descendent species?

A. Imagine an evolutionary tree of these beetles and most of them do not live with ants. They’re free-living predators that live in soil and hunt like other micro-arthropods. Many independent lineages from that kind of free-living ancestral condition have undergone this transition to life inside ant societies.

Dozens to hundreds of independent origins of this form of symbiosis have evolved within this group. It’s this amazing system of convergent evolution, when the same or similar traits evolve in response to similar selection pressures.

So here you have this entire symbiotic life style arising independently multiple times from kind of similar evolutionary starting material.

What’s really amazing is that in many of the symbiotic lineages their anatomy and their behaviors have all evolved in the same direction, too. You get species which all evolved to look like ants. You get species which evolve to look like termites and undergo this body form that enables them to mimic termites. You’d think that it’s so dramatic, how could it evolve at all? But, in fact, it’s evolved multiple times independently. And their social behaviors that they evolved are also convergent.

Q. How are you using the beetles to study this kind of evolution?

A. One way is using a free-living species. What it represents is the kind of evolutionary starting conditions for this kind of symbiosis. And so, we’re looking at its brain and its glandular chemistry and then using that as a reference species to compare with related symbiotic species.

The rove beetles looks like this sort of quirky, obscure phenomenon that no one else works on, but when you scratch the surface of it, you see really it is getting at very deep questions in evolutionary biology.

Q. So the lack of exciting insects in South Wales, where you grew up led you to an extremely exciting insect scientifically?

A. I know, exactly. I used to keep all these different tropical insects in my room and I think I wanted to just live in a rain forest and collect insects when I was seven, eight years old. But there was never anything that came close to these beetles for me and the funny thing is, they’re so tiny, you know, they’re a few millimeters long. But as soon as you put them under the microscopic, they’re absolutely beautiful and intricate and they’ve become increasingly more so the more specialized they get to live in ant societies. And to me, these symbiotic species are just the most beautiful things, so, it’s just a pleasure to work with them.

(NTY)