Can chilis bring the heat in self-defense?
A researcher explores whether pepper plants that lost avian seed dispersers boost heat to avoid being eaten by mammals.
Do chili peppers miss birds when they’re gone?
For people who enjoy spice in their diet, the heat is a chili pepper's most notable characteristic. Birds, which disperse the seeds, are attracted to the color but do not feel the heat. Do the levels of heat and color change as a result of a change in its local fauna? That’s what one Virginia Tech researcher is working to answer.
Seanne Clemente, a postdoctoral researcher in the College of Natural Resources and Environment working in Haldre Rogers’ lab in the Department of Fish and Wildlife Conservation, is studying how the disappearance of native birds on Guam may be influencing the traits of a wild chili plant known as donne’ såli.
“Our hypothesis is that without the pressure to attract birds, the plants can invest more into defense,” Clemente said. “So peppers on Guam, where there’s no pressure to attract dispersers, might be spicier.”
While the pepper is now a staple in the Mariana Islands, Spanish settlers introduced the plant centuries ago from southeastern Asia. Local communities observed that island birds quickly began visiting the shrubs and feeding on its peppers. In the Chamorro language, “donne’” means pepper and “såli” refers to the Mariana starling that has historically fed on the ripe fruit. Community knowledge and early ecological observations both describe this species as effective seed dispersers for the plant.
On Guam, however, seed dispersal was interrupted when the invasive brown tree snake eradicated the bird population over the past 80 years.
“The central question is whether plants can adapt to the loss of their natural dispersers,” Clemente said. “Around the world, many bird species are declining or going locally extinct, and plants that rely on them often suffer population declines.”
Donne’ såli turn red when they ripen, a color that attracts the starlings.
“What’s unknown is whether the plants themselves change. For example, do fruits become less [colorful] if there are no birds to attract, or do they become more attractive to maximize the few dispersal opportunities?” Clemente said.
The natural level of capsaicin in the donne’ såli is high by American standards – slightly less than habaneros but much higher than jalapenos or other commonly used peppers.
“One theory is that capsaicin evolved to select for birds as the best seed dispersers because mammals have teeth that destroy seeds,” Clemente said. “Mammals have receptors that capsaicin binds to, and our brains perceive it as heat or pain. Birds don’t have these receptors.”
She will be comparing the color and capsaicin levels within the donne’ såli on Guam to those on the islands where birds still eat the chilis and spread the seeds.
Historical and genetic evidence also link the chili’s distribution in the Marianas to bird movement. Genetic studies indicate a single introduction of the plant to the region, likely from Vietnam, with birds dispersing seeds northward across islands. More recent surveys, from Rogers’ lab, however, show a decline in chili abundance on Guam, consistent with the reduction in native birds.
Rogers, an affiliate faculty member with the Global Change Center and Invasive Species Collaborative, has long studied how changes in birds and animal populations affect plant dispersal in Guam, and how those patterns project globally as climate shifts affect plant species. Clemente’s study builds on previous work from Rogers’ lab studying which plant species in Guam depend most on animal seed dispersers, and should be targeted for conservation efforts. If the donne’ såli don’t develop a strategy for persisting without birds, a targeted plant conservation effort will be necessary to maintain this culturally important species of chili.
