Hearing in a diurnal, mute butterfly,Morpho peleides(Papilionoidea, Nymphalidae)

Abstract

Butterflies use visual and chemical cues when interacting with their environment, but the role of hearing is poorly understood in these insects. Nymphalidae (brush-footed) butterflies occur worldwide in almost all habitats and continents, and comprise more than 6,000 species. In many species a unique forewing structure--Vogel's organ--is thought to function as an ear. At present, however, there is little experimental evidence to support this hypothesis. We studied the functional organization of Vogel's organ in the common blue morpho butterfly, Morpho peleides, which represents the majority of Nymphalidae in that it is diurnal and does not produce sounds. Our results confirm that Vogel's organ possesses the morphological and physiological characteristics of a typical insect tympanal ear. The tympanum has an oval-shaped outer membrane and a convex inner membrane. Associated with the inner surface of the tympanum are three chordotonal organs, each containing 10-20 scolopidia. Extracellular recordings from the auditory nerve show that Vogel's organ is most sensitive to sounds between 2-4 kHz at median thresholds of 58 dB SPL. Most butterfly species that possess Vogel's organ are diurnal, and mute, so bat detection and conspecific communication can be ruled out as roles for hearing. We hypothesize that Vogel's organs in butterflies such as M. peleides have evolved to detect flight sounds of predatory birds. The evolution and taxonomic distribution of butterfly hearing organs are discussed.

Useless Hearing in Male Emblemasoma auditrix (Diptera, Sarcophagidae) – A Case of Intralocus Sexual Conflict during Evolution of a Complex Sense Organ?

“…Selective pressure for auditory detection of diurnal predators has not been clearly demonstrated, although some butterflies might be able to detect bird sounds [36]. In general, birds, reptiles, or predatory insects might catch E. auditrix , but no specific predator (and related sounds) has been detected.…”

“…In general, birds, reptiles, or predatory insects might catch E. auditrix , but no specific predator (and related sounds) has been detected. For example, wing beat noises have lower frequencies [36] than sensitive hearing in E. auditrix (peak at 5 kHz). Additionally, sympatric blow fly species do not possess an ear.…”

Tympanal Ears in Nyphalidae Butterflies: Morphological Diversity and Tests on the Function of Hearing

“…The neotropical Morpho peleides (Satyrinae) is a mute diurnal butterfly that possesses a well-developed Vogel's organ (Lane et al, 2008). Extracellular recordings of the N.II and N.III nerve branches of IIN1c show that M. peleides responds to low frequency sounds ranging from 500 Hz to 20 kHz with best frequencies ranging from 1 kHz -6 kHz (Lane et al, 2008;Lucas et al, 2009).…”

“…At present, the function of hearing in most nymphalid butterflies -which includes those that are diurnal and mute-is unknown. One hypothesis is that butterflies use their ears to detect bird flight sounds and/or calls (Ribaric and Gogala 1996;Mahony 2006;Lane et al 2008). From this hypothesis, certain predictions arise which can be tested.…”

“…The ears of several butterflies are tuned to low-frequency broadband sounds, usually between 2-5 kHz (Mahony 2006;Lane et al 2008;Lucas 2008). It has been shown that birds produce flight sounds that are also low-frequency and broadband (Mahony 2006;Lane et al 2008).…”