Nav: Home

Convergent con artists: How rove beetles keep evolving into army ant parasites

March 09, 2017

Marauding across the tropical forest floor, aggressive army ant colonies harbor hidden enemies within their ranks. The impostors look and smell like army ants, march with the ants, and even groom the ants. But far from being altruistic nest-mates, these creatures are parasitic beetles, engaged in a game of deception. Through dramatic changes in body shape, behavior, and pheromone chemistry, the beetles gain their hostile hosts' acceptance, duping the ants so they can feast on the colony brood.

This phenomenon did not evolve just once. Instead, these beetles arose at least a dozen separate times from non-ant-like ancestors. This discovery, published March 9 in Current Biology, provides evidence that evolution has the capacity to repeat itself in an astonishingly predictable way.

"These beetles represent a new and really stunning system of convergent evolution," says study co-author and evolutionary biologist Joseph Parker (@pselaphinae) of Columbia University and the American Museum of Natural History. "It's an elaborate symbiosis, which has evolved in a stereotyped way, multiple times from free-living ancestors."

The ant-mimicking beetles all belong to the Staphylinidae, or rove beetles, but don't mistake them for close relatives: the last common ancestor of the beetles in the study lived 105 million years ago, at about the time that humans split from mice. "What's exceptional is that this convergent system is evolutionarily ancient," says Parker. Although most other convergent systems, such as Darwin's finches, three-spined stickleback, and African lake cichlid fish, are a few million years old at most, this newly discovered example extends back into the Early Cretaceous.

Given this great age, Parker and his co-author Munetoshi Maruyama of the Kyushu University Museum argue that their finding challenges Stephen J. Gould's hypothesis that if time could be rewound and evolution allowed to replay again, very different forms of life would emerge. "The tape of life has been extremely predictable whenever rove beetles and army ants have come together," says Parker. "It begs the question: why has evolution followed this path so many times?"

Parker and Maruyama propose that although it's impossible that the beetles' most recent common ancestor was an army ant doppelganger, it probably possessed traits that would allow its descendants to readily evolve into army ant parasites. Free-living rove beetles are armed with glands that secrete defensive chemicals, so a beetle encountering an ant troop stands a much better chance of surviving than most insects do. And since rove beetles are predators, the brood of an army ant colony is an attractive food source. These traits, along with the rove beetle's body plan--flexible and able to readily evolve into an ant-like shape to deceive hosts--enabled the beetles to repeatedly infiltrate army ant societies.

"There's been this explosion of ants over the past 50-60 million years that must have radically changed terrestrial ecosystems," says Parker. "Army ants were part of that. They presented this huge niche for exploitation that these beetles were equipped to exploit, and they did so multiple times in parallel."

The paper itself focuses on DNA sequencing and reconstructing evolutionary history, but a decade of fieldwork went into collecting the beetle specimens for the study. Maruyama and Parker spent many hours in tropical forests, searching for beetles. "If you watch one of these army ant colonies for long enough, maybe one in every five thousand ants that wander past will be one of these beetles," says Parker. "You've got to have eagle eyes to pick them out."

The study opens up many questions about how this convergent system arose, some of which the researchers are starting to address by sequencing whole genomes of the rove beetles. "How predictable has molecular evolution been in each of these convergent beetle lineages? That's an obvious next step that could reveal genes involved in the ant-beetle symbiosis," says Parker.

Parker argues that discoveries like this compel us to study "underappreciated groups of organisms," he says. "If we want to understand life on Earth, we have to study groups like rove beetles. These tiny insects comprise the largest family of animals. We need to know how they live, how they evolved, and what role they play in the environment. Amazing things come from doing that."
-end-
This work was supported by Grant-in-Aid for Young Scientist B, a Sir Henry Wellcome Postdoctoral Fellowship, the NIH, and the Ellison Medical Foundation.

Current Biology, Maruyama and Parker: "Deep-time convergence in rove beetle symbionts of army ants" http://www.cell.com/current-biology/fulltext/S0960-9822(17)30198-7

Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit: http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.

Cell Press

Related Evolution Articles:

Prebiotic evolution: Hairpins help each other out
The evolution of cells and organisms is thought to have been preceded by a phase in which informational molecules like DNA could be replicated selectively.
How to be a winner in the game of evolution
A new study by University of Arizona biologists helps explain why different groups of animals differ dramatically in their number of species, and how this is related to differences in their body forms and ways of life.
The galloping evolution in seahorses
A genome project, comprising six evolutionary biologists from Professor Axel Meyer's research team from Konstanz and researchers from China and Singapore, sequenced and analyzed the genome of the tiger tail seahorse.
Fast evolution affects everyone, everywhere
Rapid evolution of other species happens all around us all the time -- and many of the most extreme examples are associated with human influences.
Landscape evolution and hazards
Landscapes are formed by a combination of uplift and erosion.
New insight into enzyme evolution
How enzymes -- the biological proteins that act as catalysts and help complex reactions occur -- are 'tuned' to work at a particular temperature is described in new research from groups in New Zealand and the UK, including the University of Bristol.
The evolution of Dark-fly
On Nov. 11, 1954, Syuiti Mori turned out the lights on a small group of fruit flies.
A look into the evolution of the eye
A team of researchers, among them a zoologist from the University of Cologne, has succeeded in reconstructing a 160 million year old compound eye of a fossil crustacean found in southeastern France visible.
Is evolution more intelligent than we thought?
Evolution may be more intelligent than we thought, according to a University of Southampton professor.
The evolution of antievolution policies
Organized opposition to the teaching of evolution in public schoolsin the United States began in the 1920s, leading to the famous Scopes Monkey trial.

Related Evolution Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#530 Why Aren't We Dead Yet?
We only notice our immune systems when they aren't working properly, or when they're under attack. How does our immune system understand what bits of us are us, and what bits are invading germs and viruses? How different are human immune systems from the immune systems of other creatures? And is the immune system so often the target of sketchy medical advice? Those questions and more, this week in our conversation with author Idan Ben-Barak about his book "Why Aren't We Dead Yet?: The Survivor’s Guide to the Immune System".