Up Close With Nature
January 14, 2013
Under the scorching sun and a very big hat, Assistant Curator of Botany Tatyana Livshultz sits eye to eye with nature. She has slowed down to the pace of the plants that surround her to watch flowers open, observe insects as they remove and deposit pollen, and look on as the flowers change color subtly before they close.
Livshultz isn’t alone, and she isn’t exactly in the middle of nowhere. Just meters from where she sits, tourists visiting the Sheding Park area of Taiwan’s Kenting National Park bustle along a path, look quizzically at Livshultz and her team, and sometimes stop to ask why the researchers are sitting in a sunny field on this hot July morning.
Livshultz’s collaborator, Research Assistant and Entomologist Ching-Wen (Karen) Tan of National Chung Hsing University, explains why she and her colleague have risen at 6 a.m. to study the park’s plants. They are working to understand the complex relationships between a member of the milkweed family, Parsonsia alboflavescens, and the animals that pollinate it, she explains.
The partnership began when Livshultz, who studies the evolution of the milkweed family, traveled to Taiwan to finalize an agreement that would allow National Taiwan University scientists to include images of Taiwanese plants housed in the Academy’s Philadelphia Herbarium in a national digital herbarium.
Since Taiwan is home to a wide variety of species in the mostly tropical milkweed family, Livshultz decided the country was the perfect place to investigate the evolution of milkweed pollination. This process of pollen transfer among a species’ flowers allows the species to reproduce and endure.
“Most flowering plants are pollinated by animals, yet the animals are inefficient at getting pollen from one plant to another, with less than 1 percent of the pollen removed being delivered to flowers of the same species,” Livshultz explains. “In one lineage of the milkweed family, which includes the common milkweed, about 25 percent of the pollen removed is ultimately delivered to flowers of the same species.”
What makes pollination so efficient in this lineage of the milkweed family? Livshultz hypothesizes that floral structures unique to this lineage securely attach pollen to insect visitors so that they can’t lose it before they reach another flower of the same species. She is testing her hypothesis by studying pollen transfer in Parsonsia, which shares many floral characteristics with the common milkweed but lacks these unique floral structures. Tan identifies insect visitors that enable pollen transfer.
“For 10 minutes every hour, we observe, count, and identify the animal visitors,” Livshultz says. “I also observe how the flowers are behaving, when they are opening, closing, and when the insects are taking nectar.”
Livshultz trained Tan to check the plants morning and evening and trace the development of buds into blossoms.
“In Taiwan, we don’t have many people studying pollination biology,” Tan says. “I wanted to learn to do the experiments and gain the knowledge and background for pollination studies.”
Livshultz and Tan caught insects for identification, checked them for pollen, and preserved them as specimens. They also conducted experiments to see which visitors removed and deposited pollen.
In the lab, Tan dissected flowers and counted pollen grains to determine the amount deposited and removed. She examined insects caught on the flowers to find out which visitors carried Parsonsia pollen. She received an Academy McHenry Fellowship, awarded to researchers conducting advanced botanical studies, to conduct this work.
Livshultz and Tan will return to Taiwan for more information, but their early observations about one of Parsonsia’s most common visitors, the butterfly Idea leuconoe, have led them to propose a hypothesis about Parsonsia’s pollen transfer strategy.
While most caterpillars avoided Parsonsia, Idea leuconoe fed on its leaves. Other butterfly species avoided Parsonsia flowers as adults too, but Idea leuconoe frequently took nectar from the flowers and carried Parsonsia pollen.
Livshultz and Tan posit that the chemical in Parsonsia’s leaves that deters other caterpillars may also be in Parsonsia’s nectar, preventing other butterflies from visiting. Tan will test Parsonsia’s nectar for the chemical.
“Plants have different ways of increasing their pollination,” Livshultz says. “One way is by limiting the spectrum of potential visitors to the most efficient pollinators.”
Idea leuconoe adults seek out Parsonsia plants as egg-laying sites. This behavior might make them better pollinators than butterfly species that target other plant species for egg-laying.
What kinds of ecological conditions might have allowed Parsonsia to develop this possible pollination strategy? How efficient is this strategy compared to that of the common milkweed, which has floral structures that make many insect species into efficient pollinators?
Natural scientists like Livshultz and Tan immerse themselves in nature to answer these kinds of questions about the relationships between plants and animals.
“About 90 percent of plant species rely on animals for pollination, and for the vast majority of those plant species, we don’t know who their visitors are, how they pollinate, and what their ecological relationship to the flowers is,” Livshultz says. “Discovering the interactions of plant and animal species as we document their diversity and distribution is part of our mission as a natural history museum.”
The Academy’s Botany Department will be the star of Botany Discovery Weekend (Saturday through Monday, January 19–21). Participate in hands-on activities and demonstrations, and mount your very own plant specimen to take home. Assist in pollinating some super-fast-growing flowers to ensure a new generation, and say hello to some of the Academy’s live animals that eat nothing but plants. Children and adults alike can hear Academy botanists discuss everything from slime molds and algae to Philadelphia’s fascinating botanical history and the scientific side of the Lewis and Clark Expedition. Visit our events page for more information.
This article was adapted from the summer 2012 issue of Academy Frontiers.