Research on bird beaks delivers insights on variation

Evolutionary biologists have long held up songbirds, particularly the Galapagos finches first described by Charles Darwin, as an example of natural selection at work. In order to exploit different environments and food sources, the birds developed a startling variety of beak shapes — from short, blunt beaks ideal for cracking seeds and nuts to long, slender beaks designed to sip nectar from flowers. The assumption was that natural selection was the primary, if not the sole, cause for the variation.

But while that variation can be tied, in part, to the way the beaks develop, Harvard researchers say that a common developmental mechanism is also a powerful constraint on new beak shapes.

A team led by Arkhat Abzhanov, an associate professor of organismic and evolutionary biology and a Grass Fellow with the Radcliffe Institute, and Michael P. Brenner, the Glover Professor of Applied Mathematics and Applied Physics and a professor of physics, has demonstrated that a shared developmental mechanism in songbirds is responsible for generating tremendous variability in their beaks, and is also a check against certain types of novel shapes. The work was described in a recent paper published in Nature Communications.

“What this study suggests is that for songbirds which use a conical-shaped beak … even though they show amazing adaptive diversity, they all generate their beaks using the same developmental mechanism, and that puts constraints on the kind of variation they are able to produce,” said Abzhanov. “Ultimately, it shows how efficiently nature can work, because these birds have been able to squeeze as much as they can from the level of variation they can actually produce.”

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