For decades, the story of spider evolution went like this: As insects became more and more diverse, with some species taking to the skies, spiders evolved new hunting strategies, including the ability to weave orb-shaped webs to trap their prey.
From that single origin, the story goes, orb-weaver spiders diverged along different evolutionary paths, leading to today, where several species weave similar though not identical webs.
It's a good story, but there's just one problem Harvard scientists now know it's not true.
The largest-ever phylogenetic study of spiders, conducted by postdoctoral student Rosa Fernndez, Gonzalo Giribet, Alexander Agassiz Professor of Zoology, and Gustavo Hormiga, a professor at George Washington University, shows that, contrary to long-held popular opinion, the two groups of spiders that weave orb-shaped webs do not share a single origin. The study is described in a July 17 paper published in Current Biology.
"This study examines two different groups of orb-weaver spiders, as well as several other species," Giribet said. "Using thousands of genes, we did a comparative phylogenetic analysis, and what we now know is there is not a single origin for the orb-weaver spiders.
"There are two possible explanations for this," he continued. "One is that the orb web evolved far back in the lineage of the two groups, but has been lost in some groups. The other option is that the orb web evolved independently in these two groups. We still haven't resolved that question yet we need to sample many more of these intermediate groups before we can say which option is correct."
The belief that orb-weaver spiders shared a common origin, Giribet said, came largely from earlier morphological studies.
Even as new genetic tools became more commonplace in the last two decades, the single origin theory held sway, in part, because early phylogenetic studies relied on just a handfu
|Contact: Peter Reuell|