23 July 2008
"Evolution never takes a vacation"
This week's column from Olivia Judson gives some examples of recent, rapid evolutionary change. She cites the evolutionary change seen in the beak size of Darwin's finches [$-a], the flowering time of Californian field mustard [$-a], and the head shape and diet of Croatian wall lizards [$-a], but misses one of my favorite recent cases: the weed Crespis sancta.
This little plant recently moved into urban Montpelier, France, wherever its seeds land on cracks in the sidewalk or end up in patches of landscaping. And that urban landscape poses a problem for C. sancta - its seeds normally disperse like a dandelion's, by floating on little feathery vanes. But if a plant is surrounded by pavement, most seeds that disperse this way will end up on pavement, unable to take root. So, as a recent study [$-a] shows, natural selection has favored a mutant C. sancta that doesn't have vanes on its seeds. Vane-less seeds land right next to their parent plant, where there's sure to be soil.
Of course, there are lots of instances of evolution in action that Judson hasn't cataloged - because, as she rightly says, it's going on everywhere, all the time: "Evolution never takes a vacation."
P. R. Grant (2006). Evolution of Character Displacement in Darwin's Finches Science, 313 (5784), 224-226 DOI: 10.1126/science.1128374
S. J. Franks, S. Sim, A. E. Weis (2007). Rapid evolution of flowering time by an annual plant in response to a climate fluctuation PNAS, 104 (4), 1278-1282 DOI: 10.1073/pnas.0608379104
A. Herrel, K. Huyghe, B. Vanhooydonck, T. Backeljau, K. Breugelmans, I. Grbac, R. Van Damme, D. J. Irschick (2008). Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource PNAS, 105 (12), 4792-4795 DOI: 10.1073/pnas.0711998105
P.-O. Cheptou, O. Carrue, S. Rouifed, A. Cantarel (2008). Rapid evolution of seed dispersal in an urban environment in the weed Crepis sancta PNAS, 105 (10), 3796-3799 DOI: 10.1073/pnas.0708446105