Auditory neuroethology: What the frog’s lungs tell the frog’s ear

Animals that communicate by vocal means must make their own calls salient against a background of environmental noise. A new study green tree frogs demonstrates input from the lungs to middle ear reduces interfering noise and thus enhances call detection. Male are highly vocal. They produce high-intensity, distinct advertisement attract females for mating defend calling spots rival males. Frogs often inhabit ponds streams containing many other callers, both conspecific (own species) heterospecific (other species). In order be heard within these dense ‘frog cocktail parties’, they regulate modify so as not drowned out others. Female approach males mating, need determine, listening, species caller whether he might fit mate. These behaviors take place only din chorus frogs, but also sounds wind, water, traffic, machinery. So how do with unusual ears, minimize interference maximize chances reproduction? An exciting in this issue Current Biology Norman Lee, Jakob Christensen-Dalsgaard, Lauren White, Katrina Schrode, Mark Bee1Lee N. Christensen-Dalsgaard J. White L.A. Schrode K.M. Bee M.A. Lung mediated auditory contrast enhancement improves signal-to-noise ratio communication frogs.Curr. Biol. 2021; 31: 1488-1498Abstract Full Text PDF PubMed Scopus (12) Google Scholar suggests animals have evolved novel solution problem. For long time, predominant theory guiding research into mechanisms acoustic was matched filter model2Capranica R.R. Moffat A.J.M. Neurobehavioral correlates sound anurans.in: Ewert J.-P. Capranica Ingle D. Advances Vertebrate Neuroethology. Plenum Press, New York1983: 701-730Crossref Scholar. This model explained discrimination noisy environment selective responsiveness nerve fibers frog’s inner frequencies calls, followed operation combination-sensitive neurons somewhere central system. has been evaluated several different frog species3Simmons A.M. To is human, frogive divine: Bob Capranica’s legacy neuroethology.J. Comp. Physiol. A. 2013; 199: 169-182Crossref (24) Scholar,4Bee Treefrogs animal models on scene analysis party problem.Int. Psychophysiol. 2015; 95: 216-237Crossref (49) Scholar, including (Figure 1) studied Lee et al.1Lee Although there populations respond best tuned non-call frequencies. Moreover, exist, them selectively calls3Simmons The can account some, all, ability separate signal al.’s advance highlight mechanism which rejected. focus processing use peripheral system, effect, adding new, third level focuses rejection. appreciate findings, let’s look at anatomy. No external ears (pinna), all an two organs (rather than one cochlea mammals) detecting low-frequency high-frequency (the amphibian basilar papilla, respectively)5Simmons Ketten D.R. How hears.Acoust. Today. 2020; 16: 67-74Crossref Many frog, tympanic membrane (eardrum) lies flat side head. Sound-induced vibrations eardrum transmitted via ossicles three cavity ear. receives opposite through large, permanently open Eustachian tubes5Simmons Interestingly, lungs. pathway first discovered experiments using laser Doppler vibrometry measure body wall Puerto Rican coqui frog6Narins P.M. Ehret G. Tautz Accessory transfer neotropical frog.Proc. Natl. Acad. Sci. USA. 1988; 85: 1508-1512Crossref (77) When waves hit thin (frogs ribs) overlying air-filled lungs, vibrate. travel up mouth tubes cavity, then existence transmission confirmed species7Ehret Keilwerth E. Kamada T. lung-eardrum treefrog four dendrobatid species: Some properties transmission.J. Exp. 1994; 195: 329-343Crossref those ‘earless’ lack eardrums entirely8Hetherington T.E. Lindquist E.D. Lung-based hearing “earless” anuran amphibian.J. 1999; 184: 395-401Crossref (39) Narins al.6Narins proposed ‘accessory pathway’ functions improve localize sounds, evidence proposal lacking9Christensen-Dalsgaard Lung-to-ear does directional treefrogs (Hyla cinerea).J. 20: jeb232421Crossref (5) develop hypothesis role lung-transmission based engineering concept ‘spectral enhancement’. argue lung acts reduce responses (that is, represented species’ call), biologically important call) consequently boosted comparison. Using female response authors resonate (respond to) present male call. act frequencies, represent unwanted noise, rather sensitivity themselves, previously proposed7Ehret addition, de-emphasis reflected — spectral sharpens fiber presented realistic levels. But effective natural environment, choose appropriate mate party? address question clever manner, analyzing citizen science data soundscapes multi-species choruses. Indeed, find same time contain fall frequency range female’s resonance. job filtering made easier her As note, we don’t yet know exact details attenuates vibrations. Is spectral-contrast effect common (body) sizes calls? predict relationship between resonance will consistent across species, part because vary inversely size. where sizes, reject differently? Does work sources or human activities, more broadband results lines relevance studying understand problem communication. Signal-to-noise frogsLee al.Current BiologyMarch 4, 2021In BriefThe characteristic large social gatherings impairs humans animals. al. show lung-to-ear unique amphibians helps breeding Full-Text Open Access