Using genetic markers, researchers have for the first time shown how cultivating a specific crop led to the expansion of a pollinator species. In this case, the researchers found that the spread of a bee species in pre-Columbian Central and North America was tied to the spread of squash agriculture.
"We wanted to understand what happens when the range of a bee expands," says Margarita López-Uribe, a postdoctoral researcher at North Carolina State University and lead author of a paper describing the work. "What does that mean for its genetic variability? And if the genetic variability declines, does that harm the viability of the species?"
To explore these questions, researchers looked at the squash bee (Peponapis pruinosa), which is indigenous to what is now central Mexico and the southwestern United States. Squash bees are specialists, collecting pollen solely from the flowers of plants in the genus Cucurbita, such as squash, zucchini and pumpkins.
Before contact with Europeans, native American peoples had begun cultivating Cucurbita crops. Over time, these agricultural practices spread to the north and east.
"We wanted to know whether P. pruinosa spread along with those crops," López-Uribe says.
To find out, researchers looked at DNA from squash bee individuals, collected from throughout the species' range. P. pruinosa can now be found from southern Mexico to California and Idaho in the west, and from Georgia in the southeast to Quebec in the north.
By assessing genetic markers in each bee's DNA, the researchers could identify genetic signatures associated with when and where the species expanded.