© Judy Gallagher
Tiny spiders may have a huge story to tell about evolution. UVM biologist Charles Goodnight helped University of Pittsburgh scientist Jonathan Pruitt unravel the tale. And from these spiders’ tangled webs, the researchers have uncovered the first-ever field-based evidence for a biological mechanism called “group selection.” Evolutionary theorists have been debating its existence and power for decades. Now Pruitt and Goodnight have observed it in the wild — as they report in the journal 'Nature.'
Along rivers in Tennessee and Georgia, scientists have been studying brownish-orange spiders, called Anelosimus studiosus
, that make cobwebby nests "anywhere from the size of a golf ball to the size of a Volkswagen Beetle," researcher Jonathan Pruitt says. The individual spiders are only the size of a pencil eraser, but they form organized groups that can catch prey ranging from fruit flies to small vertebrates
. "We have found carcasses of rats and birds inside their colonies," Pruitt says. Unlike most spiders, which are solitary, these social spiders work together in groups.
Now new research shows that they evolve together in groups
Say "group selection" among some groups of evolutionary biologists and you won't be invited back to the party. But JonathanPruitt, at the University of Pittsburgh, and Charles Goodnight, at the University of Vermont, have been studying generations of these Anelosimus
spiders - and have gathered the first-ever experimental evidence that group selection can fundamentally shape collective traits in wild populations.
Their results are presented in the Oct. 1 online edition of the journal Nature.
"Biologists have never shown an adaptation in nature which is clearly attributable to group selection," Goodnight said. "Our paper is that demonstration."