FAYETTEVILLE — Studying the secrets of how the common red milkweed beetle can safely feed on a toxic plant helps illuminate the ecological, evolutionary and economic impact of insect-plant interactions from a genomic perspective.
Although the relationship between the red milkweed beetle and milkweed plants has been studied for nearly 150 years, an Arkansas Agricultural Experiment Station scientist joined colleagues at the University of Memphis and the University of Wisconsin Oshkosh to do what no one else has done — curate the beetle’s genome and its arsenal of genes related to plant-feeding and other biological traits.
With support from the National Science Foundation, they sequenced and assembled the entire genome of the host-specialist milkweed beetle (Tetraopes tetrophthalmus). They then compared aspects of genome biology to a relative, the host-generalist Asian longhorned beetle (Anoplophora glabripennis), which is an invasive exotic species that feeds on a variety of trees important to forestry.
Their study, “Functional and evolutionary insights into chemosensation and specialized herbivory from the genome of the red milkweed beetle,” was published in the Journal of Heredity by the American Genetic Association this summer.
“From a biological standpoint, there is a lot of correspondence that suggests that longstanding interactions between milkweed beetles and their toxic milkweed hosts should influence the biology of both interacting partners,” said Rich Adams, a lead author of the study. “But, to date, no one had assembled a milkweed beetle genome, which opens the door for targeting a lot of interesting questions at the interface between insect and plant.”
Adams is an assistant professor of agricultural statistics in the department of entomology and plant pathology for the University of Arkansas System Division of Agriculture. He is also a member of the Center for Agricultural Data Analytics, a new initiative of the experiment station, and he teaches statistics courses in the Dale Bumpers College of Agricultural, Food and Life Sciences.
Scientific development
Milkweeds and milkweed beetles (genus Tetraopes) have been studied as valuable models for over a century of research into ecology, evolution, developmental biology, biochemistry of toxins and more, Adams said. They are also providing an interesting and compelling case of co-divergence patterns between insect and plant — meaning the plants and insects share similarities in the timing of co-evolution across their histories of interaction, Adams explained.
The research team showed that the red milkweed beetle has an apparent expansion of genes from the ABC transport family, which may help them feed on milkweeds and sequester its toxins inside beetle tissues. Milkweeds are renowned for their toxic latex cocktails, which affect the balance of sodium, calcium and potassium that keeps heart cells pumping. Adams said this genome provides insights into the genes the beetle has evolved to safely interact with its toxic milkweed hosts.
“Milkweeds produce a particularly nasty type of toxin called cardiac glycosides alongside other types of toxins that come with it,” Adams said. “For many insects that eat it, the toxin will block their sodium-potassium pumps. But this beetle developed a way to not only resist the toxin, but also sequester it, hold on to it, to keep the beetles themselves safe from would-be predators.”
The study also pinpointed differences in genes responsible for smell, taste and metabolic enzymes that degrade the plant cell well. Adams said it provides a new vantage point for exploring the ecology and evolution of specialized plant-feeding in longhorned beetles, and other plant-eating beetles.