Wednesday September 13, 2017

How woodpeckers and aye-aye lemurs can teach us about evolution

Harvard professor Jonathan Losos says woodpeckers have evolved to get grubs from wood by pecking a hole. In Madagascar, there are no woodpeckers so the aye-aye evolved to fill the grub-eating niche there.

Harvard professor Jonathan Losos says woodpeckers have evolved to get grubs from wood by pecking a hole. In Madagascar, there are no woodpeckers so the aye-aye evolved to fill the grub-eating niche there. (Vasily Fedosenko/Reuters)

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"It's tough … [The] logistical difficulties of getting, you know, 30,000 lbs of steel into the middle of the desert. And you know, catching mice under very hot conditions. Dodging rattlesnakes."

It's not how you would expect an evolutionary biologist to describe his daily life at work.

Rather than looking at fossils, McGill University's Rowan Barrett studies evolution in the field — with deer mice in gigantic steel cages in the fields and sandhills in Nebraska.  

Deer Mice

Deer mice living on the pale soils of the Nebraska Sandhills are lighter than deer mice from darker surrounding areas. (Rowan Barrett)

Scientists used to think evolution happened over many millennia, but it turns out that with enough environmental pressure, natural selection can be studied over the course of only a few years.

The creatures under study — whether bacteria, fruit flies or Barrett's deer mice — are often small and unremarkable.  

But the experimental results can provide answers to a longstanding debate in biology over whether evolution is predictable — or based on historical coincidences.

Evolutionary biologist Dolph Schluter studies stickleback fish and says they can shed light on human evolution. The fish are about five to seven cm long and are "not very large in reality but very large in the imagination."

"The techniques that were developed in an effort to find the gene underlying variation in spininess, bony armour, in stickleback are now being used to identify differences between humans and chimpanzees," says Schluter.

Mouse Enclosure Barrett

Rowan Barrett studies evolution in the field with deer mice and created gigantic steel enclosures in the fields and sandhills in Nebraska. (Submitted by Rowan Barrett)

Harvard professor Jonathan Losos studies lizards. He's been known to lasso anole lizards with dental floss — for the purposes of his research, and with no harm to the lizards.

He says the lizards he studies have evolved convergently — "when species independently evolve to be very similar in appearance."

Though the four Caribbean islands Losos studied, all have nearly identical species of anole lizards adapted to different environments.

Whether it's living on the ground or higher in the trees, these species evolved separately, according to Losos. They may look very similar, but they're not close relatives.

"Some people have argued that convergent evolution shows that evolution is repeatable — that it is predictable," Losos tells The Current's Anna Maria Tremonti.

Then there's the example of woodpeckers and Madagascar's aye-aye lemurs, which Losos describes as looking like "something from a nightmare."  

Jonathan B. Losos

Jonathan Losos studies lizards and says they have evolved convergently, pointing to the argument that convergent evolution shows evolution is predictable. (Riverhead)

Woodpeckers exist widely around the world, and are very well adapted to eating grubs from trees — drilling a hole in the wood with their beaks, and pulling out the grubs with their very long tongues.

But woodpeckers don't live on Madagascar, and so the aye-aye evolved to fill the grub-eating niche there.

With its big ears, giant front teeth, and incredibly long middle finger, the aye-aye can listen for the grubs, chew a hole in the wood, and scoop out the grub.

In this case, the adaptations to the same environment are very different indeed.

Humans, on the other hand, are what Losos calls an "evolutionary singleton."

"Here we are a species that's obviously extremely well adapted to the environment in which we evolved," says Losos.

"And yet nothing like us has ever evolved anywhere else in the world."

This segment is part of our season-long series Adaptation looking at the surprising, innovative, and sometimes ill-advised ways we accommodate a rapidly shifting world. 

Listen to the full segment near the top of this web post.

This segment was produced by The Current's Karin Marley.