The Scrub Jays of California’s Santa Cruz Island really love a good peanut. “It’s like crack to them,” says Katie Langin, a biologist at Colorado State University who probably knows these birds better than anyone else. Working with Scott Morrison of the Nature Conservancy, Langin started visiting the peaks and valleys of this wild island in 2007, baiting jays with nuts to trap and tag them for her dissertation. Before she came along, what researchers knew about the island scrub jay came from observations in just a handful of places. Much of this rock is inaccessible, but Langin had a helicopter.
As she gathered more and more data on different populations of the birds around the island, Langin had a revelation: The birds, members of one single species, had split into two varieties in different habitats. Island scrub jays living in oak forests have shorter bills, good for cracking acorns. Their counterparts in pine forests have longer bills, which seem better adapted to prying open pine cones. That may not appear to be something you’d consider a “revelation,” but it really is—if you believe in evolution. Ever since Darwin and his famous finches, biologists have thought that in order for a species to diverge into two new species, the two populations had to be physically isolated. Those finches, for instance, each live on a different Galapagos island, where their special circumstances have resulted in specialized bill shapes. Yet the two varieties of island scrub jay (they haven’t technically speciated—yet) live on the same tiny island. If they wanted to meet each other for a brunch of acorns and/or pine nuts and perhaps later some mating, they could just fly right over.
This is very, very weird. It’s an affront to a sacred tenet of evolution you probably learned in school: Isolation drives speciation. Well, speciation can also come about in a broadly distributed population, with individuals at one end evolving differently than individuals at the other, but nothing kicks evolution into overdrive quite like separation. Without it, two varieties should regularly breed and homogenize, canceling out something like different bill shapes (though rarely the two types of island scrub jay will in fact interbreed). And the island scrub jay isn’t alone in its evolutionary bizarreness. In the past decade, scientists have found more and more species that have diverged without isolation. Langin’s discovery with island scrub jays, published last week in the journal Evolution, is perhaps the most dramatic illustration of this yet. Via This Jay Is Evolving in a Very, Very Weird Way