Flowers emit scented chemicals to attract pollinators, but this perfume - and how pollinators interact with the plant - can go through profound changes as a crop becomes domesticated.
In a new study published in the Journal of Chemical Ecology, a team led by researchers in Penn State's College of Agricultural Sciences found that domesticated flowers have different scent chemical profiles than wild plants in several species of squash. Additionally, the specialized pollinators of these plants - squash bees - detect different compounds, called floral volatile organic compounds (VOCs) in wild plants that they co-evolved with than in domesticated plants.
Margarita López-Uribe, Lorenzo L. Langstroth Early Career Professor and senior author on the study, said the findings provide new insights into plant-pollinator interactions in agroecosystems like farms and gardens.
"In addition to squash, there are several other crops that are visited by specialist pollinators, including blueberries, tomatoes and sunflowers," she said. "Broadening our understanding of the chemical signals used by pollinators while visiting these crops may lead to better breeding strategies to enhance crop yields by improving pollination."
About 40% of land on Earth is occupied by crop plants that have been domesticated throughout the past 10,000 years, the researchers said. And, as humans bred crops to be more desirable, the plants often look, smell and taste different from their wild counterparts. Flowers produce a complex blend of VOCs that allow pollinators and other foraging insects to smell and locate them over greater areas than through vision alone, suggesting that changes in VOCs during domestication may change how pollinators perceive and interact with the plants.
"Currently, several populations of the squash bees co-exist in habitats where they exclusively interact with crop flowers that have been domesticated for thousands of years," López-Uribe said. "In this paper, we wanted to characterize the different VOC profiles of these wild and domesticated flowers and how they affect pollinator interaction."
After characterizing and identifying the VOCs in multiple species of wild and domesticated squash, the researchers performed several experiments. First, they exposed the bees' antennae to VOCs from both wild and domesticated flowers so they could see which compounds generated antennal responses, which indicate that the bees can detect these compounds.
The researchers also tracked which squash flowers attracted the most visits from bees. Then, the team used traps baited with pure versions of the VOCs to see which compounds the bees would visit the most.
The researchers found that domestication is associated with lower levels of total VOCs, with the exception of one: 1,4-dimethoxybenzene, a compound that the researchers discovered was able to attract bees when isolated.
"Interestingly, we found that 1,4-dimethoxybenzene is the only compound that persists in the heavily domesticated species crooknecks and acorn squash," López-Uribe said. "This suggests that this VOC is likely important for domesticated plants."
They also identified two other compounds positively associated with increased bee approaches and nectar drinking, as well as two compounds that tended to deter bees from these behaviors.
The researchers said that taken together, their findings demonstrate that domestication alters signals used by specialist bees to locate flowers by producing other compounds that may attract more pollinators. Next steps could include replicating the experiment in other locations and populations of the specialist bee to test whether these responses are consistent.
"These locations could include the bees' ancestral range, where they interact with both domesticated and wild plants, as well as other areas in the extended range, like Pennsylvania, where the bees exclusively interact with domesticated plants," López-Uribe said.
Avehi Singh, consultant at the World Wildlife Fund; Andrew Myrick, assistant research professor at Penn State; Nathaniel McCartney, research technician at Penn State; Jared Ali, associate professor of entomology at Penn State; Swayamjit Ray, University of Arkansas at Little Rock; and Kristen Brochu-DeLuca, University of The Bahamas, co-authored the study.
The U.S. National Science Foundation, United States Department of Agriculture's National Institute of Food and Agriculture, and the Pennsylvania State University Lorenzo L. Langstroth Endowment funds helped support this research.
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