10. The Social Behavior of Sweat Bees and Global Warming
Bryan Danforth
Bryan N. Danforth, Entomology, and colleagues linked the social evolution of many species of sweat bees (Halictid bees) with a period of global warming that occurred 20 to 22 million years ago. This is more recent than scientists had thought, particularly when compared to other insects that evolved 65 million years ago. Danforth believes that climate change was a critical factor in the evolution of behavior in these eusocial bees (bees that have permanently sterile worker castes). His study used both fossils and 2,300 base pairs of DNA sequences from three genes to infer the bees’ evolutionary history (phylogeny). The DNA sequencing showed how divergent the various species are from one another, while the fossils allowed the researchers to represent the phylogeny on a timeline of millions of years. The researchers next asked what was happening 20 to 22 million years ago that would cause the development of social behavior in so many species at the same time. They discovered that the Earth underwent a warming trend from 15 to 26 million years ago. Halictid bees—important native pollinators in the Northern Hemisphere, where there are about 1,000 species—are nicknamed sweat bees because they are attracted to the salts in human perspiration.