Where Dung Beetles Perch Says a Lot About Community Evolution
By Andrew Porterfield
For animals, the ability to survive and thrive depends on how good they are at procuring food. For most animals, there are three foraging options: search actively for food, sit and wait for a signal indicating food, or a combination of the two. For many species of dung beetles, the “sit and wait” strategy is used to await the arrival of feces spread by other animals.
What’s not known is why they choose this strategy. What is the evolutionary driver of this behavior, and why is it rewarded over other strategies? Jorge Noriega, Ph.D., associate researcher at Universidad de los Andes in Bogotá, Colombia, and Kevina Vulinec, Ph.D., professor of agriculture and natural resources at Delaware State University, conducted a comprehensive literature search to discover what was known about feeding behavior in dung beetles. While they found that relatively few studies have been conducted in this area, nonetheless they concluded that the main driver of perching “sit and wait” behavior was spatial segregation, a type of resource partitioning that helps animals obtain food in the face of heavy competition. Noriega’s and Vulinec’s study was published in November 2020 in the Annals of the Entomological Society of America.
In their study, Noriega and Vulinec found 46 articles on dung beetle behavior that were relevant to their review. In the literature, six hypotheses were presented to explain the beetles’ perching tactics: resource partitioning, food detection, time spent foraging, avoiding predators, temperature regulation, and resting.
“It was interesting to find very few studies and especially very few experimental setups” in their literature search, Noriega says. “There are big biogeographic areas without any study. This paper is part of the field studies we are doing in the Neotropical region, especially in Colombia, for the last 20 years to understand the ecology and natural history of dung beetles.”
Perching in dung beetles was first recorded around 1900. The behavior consists of the beetle sitting on a leaf, facing the wind with its head raised, waiting for the scent or chemical signal of dung nearby. The forelegs are poised under the prothorax, while the hind legs are spread alongside the body. To aid in chemoreception, the antennae of dung beetles have evolved to perceive food from miles away.
Spatial segregation, Noriega and Vulinec propose, has resulted from the adoption of different perching heights as a function of the beetle’s size. Larger, heavier beetles prefer bigger leaves, and different groups will perch at different heights. Perching heights varied from 3 to 250 centimeters (about two inches to eight feet). Meanwhile, very large species (over 22 millimeters, or about 1 inch) were not found perching. Thus, the beetles could obtain dung by reducing the possibility of competition among beetle groups. “In general terms, there are more species doing perching than following animals,” Noriega says. “Only the big dung beetles could invest in this kind of behavior (following), because flying is costly in terms of energy. Small species could sit and wait and perch, but they must be sure to find great resources.”
Noriega and Vulinec warn, however, that even this hypothesis only has five studies addressing it. “There is a widespread lack of natural history information about this behavior and the ecological implications in tropical forests,” they write. More exploration in different geographic regions, and experimental studies on all six hypotheses about feeding behavior (and the possibility of others), needs to be done. They add that the effect of human disturbance in forested areas is another valuable area of study.
“It is important to understand the evolutionary mechanisms that regulate food partitioning in ecosystems with high diversity and potential high competition,” Noriega says. “If we understand how this behavioral strategy works, we could understand how communities are structured.”
Annals of the Entomological Society of America
Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.