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PELLSTON, Michigan.—The unassuming mite, a minuscule invertebrate that commonly resides in tiny chambers underneath leaves, plays a crucial role in defending its host plants against adversaries.
A study from the University of Michigan revealed that plants with a higher quantity of domatia—small compartments formed by microscopic hairs on the leaf undersides—also supported a significantly greater number of mites compared to species without domatia. The research, spearheaded by U-M researcher Marjorie Weber, associate professor of ecology and evolutionary biology, involved numerous U-M undergraduate students at the U-M Biological Station in Pellston, Michigan.
“The mites residing in domatia consume plant pathogens and pests. They are fungivorous (feeding on fungi) and herbivorous (preying on small herbivores),” said Weber. “An increase in mites translates to enhanced protection for the plants. By targeting small pests, the mites help in maintaining clean leaves.”
Mite domatia have historically been neglected in scientific research; however, in regions such as the forests of Michigan, they contribute significantly to tree protection, Weber noted. This relationship operates as a mutual benefit, where mites devour smaller herbivores and pathogens on the leaves in exchange for shelter within the domatia.
Weber created the study as a component of a course she designed for U-M students, titled “Insights from Trees: Science, Art and Observation in a Noisy World.” This class made its debut in the summer of 2024 at the U-M Biological Station. As part of the curriculum in July 2024, students assessed mite abundance on foliage from various woody plant species.
Mites are central to Weber’s research on plant-protecting animals and other phenomena of evolution—an endeavor for which she was awarded a National Science Foundation CAREER grant exceeding $1 million. Her studies include pollinators, instances where animals defend trees (with ants and mites acting as bodyguards), and the methods by which trees shield themselves from pests and diseases. The grant also facilitated the design and support for the course at the Biological Station.
“Plants have developed remarkable attributes to promote mutualistic associations, creating adaptations to attract and maintain protective partners,” Weber explained. “In this instance, we systematically examined a forest at the Biological Station for one of the most prevalent and ancient defensive mutualism traits: mite domatia.”
Conducting Research
Weber’s assignment for her undergraduates built upon existing research linking domatia and mite populations in other forests outside of Michigan.
The class assessed the 16 most prevalent woody species for the presence and number of mite domatia, discovering that 80% of common woody species in the forest possessed mite domatia, marking the highest reported rate of mite domatia in any survey conducted to date.
As they traversed the forest, the students collected five leaves from up to 10 plants for each species, placing the leaves in plastic bags with a damp paper towel to prevent mites and leaves from drying out and wilting.
The class then transported the bagged leaves to the laboratory, utilizing microscopes to analyze the presence and abundance of domatia and mites under Weber’s oversight and the guidance of Ph.D. students from her lab.
To assess their findings, the team employed a series of phylogenetic models, testing whether the number of mites observed on a leaf correlates with the quantity of domatia on that leaf while considering the variation across the 16 species evaluated.
A Collaborative Partnership
Their investigation revealed that plants equipped with mite domatia harbored a notably larger number of mites on their leaves compared to species without mite domatia, and those with a higher number of domatia supported more mites.
The research additionally highlights northern temperate forests as a promising landscape for future studies on mite–plant mutualisms at high densities.
“The most thrilling finding for me is that Michigan forests are a hub for cooperation. Several common trees in Michigan benefit from this symbiotic relationship, including economically and ecologically significant species like maple, oak, and beech,” Weber asserted. “Another critical insight: Distantly related species of Michigan trees are converging on this strategy of collaboration with beneficial mites.”
This study represents a first co-authorship opportunity for undergraduate students 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, contributing to the project.
“It was a far-fetched aspiration of mine to engage in research and to be recognized as a published scientific author, but I never imagined I would accomplish this with such an incredible support system before completing my undergraduate studies,” remarked Lauren Jones, a senior in the U-M Program in the Environment who is concurrently a first-year graduate student in the U-M School for Environment and Sustainability through an accelerated master’s program.
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