Looking to the Future at AOU

By John W. Fitzpatrick, Cornell Lab Director
Rufous-collared Sparrow
Rufous-collared Sparrow. Photo by Dario Sanches via a Creative Commons license and the Field Guide: Birds of the World Flickr group.

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Most scientific meetings, like last week’s AOU, begin each morning with a plenary in which a prominent scientist offers the perspective of decades of experience. But on the last morning, age yielded the floor to four young scientists (“newly minted Ph.D.s” in local parlance). Three were in the running for this year’s Young Professional Award: Dan Barton, Andrea Townsend, and Zachary Cheviron. The fourth was last year’s winner, Renée Duckworth.

Cornell Lab director John Fitzpatrick found it “one of the most stimulating sessions I’ve ever attended at an AOU meeting.” –Hugh Powell

Leading off the session was Dan Barton, from the University of Montana, who has spent his Ph.D comparing clutch sizes and other life history traits across birds on three continents. He’s trying to crack a standing problem in evolutionary ecology: understanding why birds lay such different numbers of eggs in different parts of the world. Barton tested David Lack‘s classic hypothesis—that birds lay exactly as many eggs as they can expect to provision with the food available in their environment—against a popular alternative, that clutch size is molded not by food, but by mortality patterns in eggs, juveniles, or adults. Barton measured clutch sizes, nestling-provisioning rates, nest success, and adult mortality in a suite of species in North and South America, Europe, and Africa. He also removed eggs from some nests to see whether parents adjusted their schedule of feeding nestlings. In the end, he found strong evidence favoring both clutch-size hypotheses—depending on which species was involved. Long-lived species spent less effort on smaller broods, thus conserving their own energy for future opportunities to reproduce. Species with lower annual survival diligently fed their young regardless of brood size, reflecting a “go-for-it-all-now, for tomorrow I die” approach. For the latter species, food limitation appears to play the biggest role in determining clutch size.

Cornell’s Andrea Townsend followed with an elegant presentation of field data on the frequency of inbreeding in the American Crow. Incest is so consistently detrimental that it’s very rare in the natural world, requiring Andrea to devise a brand-new theoretical model to explain how it might happen with such regularity in crows. Andrea studies a large population of color-marked crows in Ithaca, N.Y., and has documented mothers breeding with sons or nephews as well as unexpectedly common cousin-cousin matings. And the crows don’t seem to be getting away with it—Andrea found that inbred offspring succumbed to diseases much more frequently than “normal” crows. Her model showed, however, that under certain conditions inbred groups could produce more total genetic representation in future generations than in outbred groups, despite the cost of losing many offspring to disease. Andrea suspects that inbreeding is maintained around Ithaca because the vast rural areas surrounding the town, where exposure to disease and environmental toxins is lower, offer a ready supply of crows. She is turning her attention to testing this idea with more studies of rural crows.

The third Young Professional finalist—and the eventual winner—was Zach Cheviron, now a postdoctoral fellow at the University of Nebraska. (Mike Webster blogged about Zach’s research on the high-altitude adaptations of the Rufous-collared Sparrow last week.) One great detail to add to Mike’s account: It turns out that at low elevations, where oxygen is plentiful, the type of hemoglobin common in high-altitude sparrows actually has trouble releasing its oxygen. Congratulations Dr. Cheviron!

Renée Duckworth, last year’s winner, batted clean-up with a superb presentation on a “bluebird cycle” of invasion and resilience going on across the West. She showed that Western Bluebirds are colonizing new areas and in some cases displacing Mountain Bluebirds. The Western Bluebirds that do this turn out to be significantly, and genetically, more aggressive than those in sedentary populations, giving them an advantage in taking over nest cavities from birds such as Tree Swallows and Mountain Bluebirds. In an amazing twist, however, the aggressive-type Western  Bluebirds are less successful at producing young than sedentary, “peaceful” individuals! Thus, after only two or three generations (about five years) non-aggressive individuals begin to prevail. Despite the spread of Western Bluebirds, Mountain Bluebirds will likely remain part of Western ecosystems, because they are are better at producing young in harsh conditions of high elevations. This “bluebird cycle” seems to be under way across the West–Mountain Bluebirds being replaced by aggressive Western Bluebirds, which in turn are replaced by nonaggressive Western Bluebirds, with Mountain Bluebirds retaining the upper hand at high elevations or after especially severe springs.

Four brilliant young investigators made for a vibrant last morning at the AOU. Without question, this is why we come to these meetings – to soak up the latest news in our unending quest to uncover the mysteries of how nature works. From the looks of it, future meetings are only going to get more interesting.

The Cornell Lab

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