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Caterpillar Warning Signals Originated From Walking

April 14, 2010

The hair-like structures used by birch caterpillars to communicate warnings may have evolved from walking, researchers from Carleton University in Ottawa, Canada have discovered.

The research team, led by Dr. Jayne Yack from the university, published their findings in the Nature Communications journal. Their report was entitled “The evolutionary origins of ritualized acoustic signals in caterpillars” and was published in the April 12 issue.

In the abstract accompanying their report, the scientists write, “Animal communication signals can be highly elaborate, and researchers have long sought explanations for their evolutionary origins. For example, how did signals such as the tail-fan display of a peacock, a firefly flash or a wolf howl evolve? Animal communication theory holds that many signals evolved from non-signaling behaviors through the process of ritualization.”

“We examine the origins of vibratory territorial signals in caterpillars using comparative and molecular phylogenetic methods,” they continue. “We show that a highly ritualized vibratory signal–anal scraping–originated from a locomotory behavior–walking. Furthermore, comparative behavioral analysis supports the hypothesis that ritualized vibratory signals derive from physical fighting behaviors. Thus, contestants signal their opponents to avoid the cost of fighting.”

Birch caterpillars drag a series of hair-like structures on their hindquarters across a leaf whenever an intruder enters their territory, creating a scraping sound that acts as a warning. Ultimately, the signal scares off the other creature, thus helping both to avoid a conflict.

Joining Yack on the research team were colleagues Jaclyn L. Scott, Abeer Sami, and Myron L. Smith from the Carleton University Department of Biology; Akito Y. Kawahara or the University of Maryland’s Department of Entomology; Jeffrey H. Skevington of the Canadian National Collection of Insects, Arachnids and Nematodes; and Shen-Horn Yen of Taiwan’s National Sun Yat-Sen University.

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