This social evolution occurred much more recently than scientists ever thought -- only 20 million to 22 million years ago, compared with the social evolution of other insects, which evolved more than 65 million years ago.

"We believe that climatic change was a critical factor in the evolution of social behavior in these bees," said Bryan Danforth, associate professor of entomology at Cornell. Sweat bees are eusocial, he explained, which is a type of social behavior in which the animals have permanently sterile worker castes (among other traits). Eusocial animals include honey, bumble, carpenter and sweat (halictid) bees, ants, termites, many wasps as well as certain kinds of shrimp and the naked mole rat.

Danforth's study, to be published in a forthcoming issue of the Proceedings of the Royal Society of London, Series B, Biological Sciences, used both fossils as well as more than 2,300 base pairs of DNA sequences from three genes to infer the evolutionary history, or phylogeny, of the family's eusocial lineages and their relatives. The DNA sequencing sheds light on how divergent the various species are from each other, and the fossils allow the researchers to represent the phylogeny in terms of a timeline in millions of years.

In 2002 and 2004, Danforth showed that the social evolution of the various species of halictid bees arose multiple times independently. The study on the timing of that social evolution, however, began as an honors thesis for former Cornell undergraduate Adam Pearson '03, now a graduate student at the University of Connecticut, in collaboration with Danforth and two former Cornell postdoctoral researchers, Sean Brady and Sedonia Sipes.

"What's so interesting is that the social behavior that's characteristic
'"/>

Contact: Press Relations Office
pressoffice@cornell.edu
607-255-6074
Cornell University News Service
13-Mar-2006