Galapagos finches yield new evolutionary insights
Scientists from McGill and UMass Amherst see the seeds of speciation in progress
Researchers from the Ď㽶ĘÓƵ, University of Massachusetts Amherst and Randolph Macon College have discovered an interesting pattern of natural selection among finches of the Galapagos Islands. The rarely seen pattern known as “disruptive natural selection” offers a glimpse into the inner workings of speciation, or how new species arise from common ancestors, and the central role that environmental conditions play in the process, the researchers said.
The study was co-authored by Dr. Andrew Hendry and Luis De Leon of McGill, Dr. Jeff Podos of UMass Amherst and Dr. Sarah Huber of Randolph Macon College in Ashland, VA. Their results were published in the current issue of the Proceedings of the Royal Society B. Biological Sciences.
The co-authors studied the role of environmental factors in evolution among the island finches of the Galapagos Islands made famous by Charles Darwin.
“Strong selection of this type is expected during speciation but is rarely studied. It was particularly inspiring to find evidence for this process in Darwin’s original muse, finches of the Galapagos. These birds are still informing Darwin’s ’mystery of mysteries’ 150 years after he published his groundbreaking book, On the Origin of Species” said Hendry, of McGill’s Redpath Museum and Department of Biology.
“Up to now,” said Podos, “scientists have speculated and made predictions about how we might explain the rise of different species in the same geographic area from a common ancestor, but it’s rare to actually be able to watch a population as it pulls apart. In our study on Santa Cruz, we’re seeing some situations that fit the predictions. Witnessing this dynamic tug of war among environmental factors is very exciting.”
The three-year study was conducted at a dry forest site known as El Garrapatero. Capturing a situation thought to prevail during the onset of speciation, the researchers discovered a strong pattern within one finch species where most individuals had either large or small beaks, a very rare phenomenon called bimodality. These finches mate with their own type (large with large and small with small) and individuals with intermediate beak sizes show low survival. These are exactly the conditions expected when adaptation to new environments, here different seed types, drives the origin of new species. These findings provide rare direct evidence of the process that Darwin predicted 150 years ago.
The researchers have not actually witnessed the birth of a new finch species; in different conditions, selection may be less intense and medium-beaked populations may rebound. But understanding the relative strength of disruptive selection in different environmental directions could provide key insights into the speciation process.
Prof. Andrew Hendry is on sabbatical and
available for print/radio interviews until Nov. 16;
He will be available for television interviews as well after Nov.
16: