May 26, 2010

Swarming Locusts Have Bigger Brains

Scientists reported that swarming locusts not only look different and act differently to solitary locusts; they also have much larger brains.

Scientists at the University of Cambridge captured images of the results of dramatic changes inside the insects' heads.

The team said the same locust could switch between a "solitary" and swarming phase.

They reported their findings in Proceedings of the Royal Society B.

"Normally locusts would avoid close contact with each other," Dr Swidbert Ott of the UK's University of Cambridge, told BBC News. "It's only when they are forced to be in close contact that they change dramatically."

This survival mechanism occurs when the insects run out of food and are forced together onto any remaining patches of vegetation.

"So they have to travel in this massive swarm to find the new patches," Ott told BBC.

Ott and his Cambridge colleague Dr Stephen Rogers converted some of them into the solitary phase by keeping them in isolation for three generations.

"Solitarious locusts are a real pain to keep," he told BBC. "You can't keep them together or they will change, so every one is kept like a race horse in its little stable - we have about 100 individual boxes with all the supplies they need."

At the conclusion of this three-generation breeding program, the scientists imaged and measured the insects' brains.

The researchers discovered that the brains of gregarious locusts were 30 percent larger.

"You find that brain regions specifically to do with things like learning and memory are massively enlarged in the gregarious ones," Ott explained to BBC.

This difference makes evolutionary sense.

"Inside the swarm, they're swamped with information," he said.

"The higher bits of the brain that deal with complexity allow them to make sense of the mayhem going on around them."

Ott and his team previously found that a signally chemical in the brain, known as serotonin, was crucial in this sudden change in the insects' behavior.

When this change occurs, the locusts also change in color and even body shape.

"People used to think that the two phases were actually two different species," Ott told BBC.

He concluded: "Being inside these swarms is really a messy business - it's driven by hunger and the need to figure out where to find new food.

"These insects even turn to cannibalism - if you're not quick enough you turn into lunch, so the [big] brain gives them the edge in a cut throat situation."


Image 1: Portrait of a Desert locust in the swarming gregarious phase, with a schematic view of the brain within the head (the brain image was obtained by computer-assisted microscopy). Image credits: Swidbert R. Ott (brain image and composition) and Tom Fayle (locust portrait), both University of Cambridge.

Image 2: A solitarious male Desert locust (left) facing a gregarious male (right) of the same species. Shown above them are their brains as revealed by computer-assisted microscopy. The solitarious locust is slightly larger and has disproportionately large eyes, yet the swarming gregarious locust has the bigger brain. The brains also have very different proportions: in gregarious locusts, the central part of the brain (shown in solid yellow) is disproportionally larger than the optic lobes (shown in translucent yellow), which process the visual information provided by the eyes. Image credits: Swidbert R. Ott (brain images and composition) and Tom Fayle (locust portraits), both University of Cambridge.

Image 3: A solitarious male Desert locust (left) facing a gregarious male (right) of the same species. In the swarming gregarious phase, locusts are smaller on average, and have disproportionately smaller eyes and shorter antennae. The postural differences shown by the two animals are characteristic, with solitarious locusts typically walking with a creeping gait close to the substrate, and gregarious locusts having a more upright carriage. Image credits: Tom Fayle, University of Cambridge.


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