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Mechanoreception |
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Ultrasonic Hearing of
Night Flying Butterflies
Department of Biology, Erindale College, University
of Toronto Summary Bats impose an impressive, if underestimated, selective force on the defensive sensory systems and behaviors of insects (Fullard 1998). Whereas most nocturnal moths have evolved simple ears with which to detect the echolocation signals of hunting bats (Roeder 1967), other non-auditory defenses exist such as flying close to the ground and, for most butterflies, flying exclusively during the day (Morrill and Fullard 1992). Certain insects have evolved dramatic changes to their day/night flight preferences and corresponding sensory alterations have appeared as a result (e.g. the "bat-deafness" of certain day-flying Venezuelan moths (Fullard et al. 1997)). The converse condition occurs for a group of neotropical butterflies, the Hedyloidea, which were described as night-flying by Annette Aiello (1992) of the Smithsonian Tropical Research Institute in Panamá, a region with intense selection pressures by bats. Malcolm Scoble's (1986) description of a tympanal organ resembling an ear on the underside of the forewing in an hedylid suggested that these butterflies have ultrasonic hearing similar to that of moths. In collaboration with Annette Aiello and Annemarie Surlykke of Odense University, Jayne Yack investigated whether night-flying Panamánian hedylids would respond to ultrasonic signals that contained the frequencies and intensities of echolocating bats. She exposed free-flying individuals of Macrosoma heliconiaria on Isla Barro Colorado, Panamá to ultrasound while videotaping their flight responses. The butterflies reacted to the sounds with the erratic twists and spins that resembled flying moths when they hear an approaching bat. With the assistance of Elisabeth Kalko of Tubingen University, Dr. Yack further determined that M. heliconiaria are palatable to the bats they fly with and we conclude that this unusual group of night-flying butterflies have evolved ears with which to detect and escape the attacks of insectivorous bats. References Aiello, A. (1992) In: Insects of Panamá and Mesoamerica. (ed. D. Quintero & A. Aiello) Fullard, J.H. (1998) In: Comparative Hearing: Insects (ed. R.R Hoy, A.N. Popper & R.R Fay) Fullard, J.H., Dawson, J.W., Otero, L.D., & Surlykke, A. (1997) J. Comp. Physiol. A 181: 477-483 Morrill S.B. & Fullard, J.H. (1992) Can. J. Zool. 70: 1097-1101 Roeder, K.D. (1967) Nerve cells and insect behavior Scoble, M. J. (1986) Bull. Br. Mus. Nat.Hist. (Entomol.) 53: 251-286. Copyright: This document is composed of unpublished material by James Fullard.
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