Feeding on an exotic weed rather than their usual diet of native plants appears to help white peacock butterflies fight off viral infections. The finding points to the ability of certain species to take advantage of new flora introduced into their environment to boost their chances of survival.
at the University of Nevada, Reno, and her colleagues wanted to examine the effect of diet on white peacock butterflies (Anartia jatrophae) 鈥� a large black and whitish butterfly species typically found in the south-eastern US and occasionally seen as far away as New Jersey and Wisconsin. While conducting a field survey in Florida, Muchoney discovered that white peacock butterflies frequently suffered from an infection caused by a virus called Junonia coenia densovirus (JcDV). This virus can interfere with the butterflies鈥� metamorphosis from caterpillar to butterfly, as well as its ability to shed its skin.
Other scientists had previously observed white peacock butterflies feeding on buckhorn plantain (Plantago lanceolata), an exotic weed that European settlers supposedly introduced to the US a few hundred years ago. They also noted that the caterpillars raised on this weed experienced delayed development and larger pupae size.
Advertisement
鈥淪o we got the idea to investigate how consuming this exotic plant could impact other aspects of this butterfly 鈥� like the ability to defend against the viral infection,鈥� Muchoney says.
The team reared two sets of white peacock caterpillars on separate diets. One group was fed the leaves of water hyssop (Bacopa monnieri), a native herb, while the other was raised on the leaves of the exotic buckhorn plantain. When the caterpillars matured, the researchers introduced densovirus into their diet. 鈥淯sing a tool like a hole puncher, we punched out a little portion of the leaf, then pipetted a quantity of virus onto the surface of the leaf and fed it to the caterpillars,鈥� says Muchoney.
The team found that the virus-infected caterpillars reared on the exotic plant were 11 times as likely to survive compared with those that fed on native plants. Additionally, even among dying caterpillars, the viral load was nearly 200 times higher in those that ate native herbs compared with those that ate the exotic weed.
But the researchers are not entirely sure what led to this outcome. In butterflies, cells called haemocytes serve as the primary defenders against invading pathogens such as bacteria and viruses. However, when comparing the two groups of caterpillars, Muchoney and her team observed no significant differences in haemocyte production. They plan to investigate further and also explore how these laboratory results relate to the butterfly population in their natural habitat.
Exotic species are increasingly common in natural habitats. So it is important to understand how native herbivores are adapting to this changing environment. And it isn鈥檛 just butterflies, says Muchoney. 鈥淪uch adaptation could become increasingly common in other species as well,鈥� she says.
While the study is intriguing, exotic plants have wider ecological impacts and long-term effects on native plants and herbivores than simply helping a species survive, says at the Florida Museum of Natural History. The advantages for one species may not necessarily extend to other species. 鈥淛ust because an exotic plant benefits a native species, that doesn鈥檛 necessarily mean we should begin planting them,鈥� he says.
Ecology Letters
