Study: Mite Domatia and Associated Mite Density in a North American Eastern Deciduous Forest in Michigan
PELLSTON, Michigan.-The humble mite, a tiny invertebrate that typically lives in small chambers on the underside of leaves, plays a mighty role in defending their host plant from invaders.
A University of Michigan study found that plants that had more domatia-those chambers made by tiny hairs on the underbellies of leaves-also had significantly more mites on their leaves than species that lacked domatia. The study, led by U-M researcher Marjorie Weber, associate professor of ecology and evolutionary biology, was carried out by a host of U-M undergraduate students at the U-M Biological Station in Pellston, Michigan.
"The mites that occupy domatia eat plant pathogens and pests. They are fungivorous (eat fungi) and herbivorous (eat small herbivores)," Weber said. "More mites means more protection for the plants. By eating small pests, the mites clean the leaves."
Mite domatia have been historically overlooked in research, but in places like the forests of Michigan, they play a large role in protecting trees, Weber said. It's a two-way street where mites might eat smaller herbivores and pathogens on the leaf and then protect the plant in exchange for shelter in the domatia.
Weber developed the study to be part of a course she designed for U-M students, titled "Insights from Trees: Science, Art and Observation in a Noisy World." The class debuted during summer 2024 at the U-M Biological Station. As part of the curriculum in July 2024, the students evaluated the abundance of mites on foliage from woody plant species.
Mites are a focus of Weber's research studying plant-protecting animals and other wonders of evolution-work for which Weber was awarded a more than $1 million National Science Foundation CAREER grant. She studies pollinators, cases where animals protect trees (ants and mites serving as bodyguards to plants) and the way trees defend themselves from pests and plant disease. Weber also used the grant to design and support the course at the Biological Station.
"Plants have evolved remarkable traits to facilitate mutualistic relationships, developing adaptations to attract and sustain protective partners," Weber said. "Here, we systematically surveyed a forest at the Biological Station for one of the most common and ancient defense mutualism phenotypes: mite domatia."
Performing research
Weber's assignment for her undergraduates built on previous work linking domatia and mite abundance in other forests outside of Michigan.
The class scored the 16 most common woody species for the presence and number of mite domatia and found that 80% of common woody species in the forest had mite domatia, the highest reported percentage of mite domatia in any survey ever conducted.
Walking their way through the forest, the students sampled five leaves per plant for up to 10 plants for each species. They put the leaves in plastic bags with a damp paper towel and stored them in a cooler to keep mites and leaves from dehydrating and withering.
The students took the bagged-up leaves to the lab where the class used microscopes to quantify domatia and mite presence and abundance under the guidance of Weber and Ph.D. students in her lab.
To evaluate their samples, the team conducted a series of what are called phylogenetic models, which test whether the number of mites found on a leaf are related to the number of domatia on that leaf, taking into account the variation in leaves found across 16 species they examined.
A cooperative agreement
Their research showed that plants with mite domatia had significantly more mites on their leaves than species that lacked mite domatia, and that plants with more domatia had more mites.
The study also points to northern temperate forests as a promising system for studying mite-plant mutualisms in high densities in the future.
"The most exciting result for me is that Michigan forests are a hotspot for cooperation. Many of the common trees in Michigan are protected by this mutually beneficial relationship, including economically and ecologically important species of maple, oak and beech," Weber said. "Another important takeaway: Distantly related species of Michigan trees are converging on this strategy of cooperating with beneficial mites."
The study is a first co-authorship for undergraduate students who were enrolled in the Insights From Trees course during the four-week summer 2024 term, including Lillian Bailey, Ashley Cole, Bailee Duke, Liam Estill, Lauren Jones, Gabrielle Leon and Nia Paton. Samantha Molino and Addison Yerks were also undergraduate student researchers at the Biological Station last year who helped on the project.
"It was a far-fetched dream of mine to be able to conduct research and to be a published scientific author, but I never dreamed that I would be able to achieve that with such a wonderful support system before I received my undergraduate degree," said Lauren Jones, a senior in the U-M Program in the Environment who is simultaneously a first-year graduate student in the U-M School for Environment and Sustainability through an accelerated master's program.
