Abstract
We measured the auditory responses of the noctuid moth Noctua pronuba to bat echolocation calls which were manipulated independently in time and frequency. Such manipulations are important in understanding how insect hearing influences the evolution of echolocation call characteristics. We manipulated the calls of three bat species (Rhinolophus hipposideros, Myotis nattereri and Pipistrellus pipistrellus) that use different echolocation call features by doubling their duration or reducing their frequency, and measured the auditory thresholds from the A1 cells of the moths. Knowing the auditory responses of the moth we tested three predictions. (i) The ranking of the audibility of unmanipulated calls to the moths should be predictable from their temporal and/or frequency structure. This was supported. (ii) Doubling the duration of the calls should increase their audibility by ca. 3 dB for all species. Their audibility did indeed increase by 2.1-3.5 dB. (iii) Reducing the frequency of the calls would increase their audibility for all species. Reducing the frequency had small effects for the two bat species which used short duration (2.7-3.6 ms) calls. However, the relatively long-duration (50 ms), largely constant-frequency calls of R. hipposideros increased in audibility by 21.6 dB when their frequency was halved. Time and frequency changes influence the audibility of calls to tympanate moths in different ways according to call design. Large changes in frequency and time had relatively small changes on the audibility of calls for short, largely broadband calls. Channelling energy into the second harmonic of the call substantially decreased the audibility of calls for bats which use long-duration, constant-frequency components in echolocation calls. We discuss our findings in the contexts of the evolution of both bat echolocation call design and the potential responses of insects which hear ultrasound.
Full Text
The Full Text of this article is available as a PDF (185.7 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Faure P. A., Fullard J. H., Dawson J. W. The gleaning attacks of the northern long-eared bat, Myotis septentrionalis, are relatively inaudible to moths. J Exp Biol. 1993 May;178:173–189. doi: 10.1242/jeb.178.1.173. [DOI] [PubMed] [Google Scholar]
- Fullard J, Dawson J. The echolocation calls of the spotted bat Euderma maculatum are relatively inaudible to moths. J Exp Biol. 1997;200(Pt 1):129–137. doi: 10.1242/jeb.200.1.129. [DOI] [PubMed] [Google Scholar]
- Hoy R. R., Robert D. Tympanal hearing in insects. Annu Rev Entomol. 1996;41:433–450. doi: 10.1146/annurev.en.41.010196.002245. [DOI] [PubMed] [Google Scholar]
- Jones G. Scaling of echolocation call parameters in bats. J Exp Biol. 1999 Dec;202(Pt 23):3359–3367. doi: 10.1242/jeb.202.23.3359. [DOI] [PubMed] [Google Scholar]
- Jones G., van Parijs S. M. Bimodal echolocation in pipistrelle bats: are cryptic species present? Proc Biol Sci. 1993 Feb 22;251(1331):119–125. doi: 10.1098/rspb.1993.0017. [DOI] [PubMed] [Google Scholar]
- Rydell J., Arlettaz R. Low-frequency echolocation enables the bat Tadarida teniotis to feed on tympanate insects. Proc Biol Sci. 1994 Aug 22;257(1349):175–178. doi: 10.1098/rspb.1994.0112. [DOI] [PubMed] [Google Scholar]
- Stapells D. R., Picton T. W., Smith A. D. Normal hearing thresholds for clicks. J Acoust Soc Am. 1982 Jul;72(1):74–79. doi: 10.1121/1.388026. [DOI] [PubMed] [Google Scholar]
- Waters D. A., Jones G. Echolocation call structure and intensity in five species of insectivorous bats. J Exp Biol. 1995 Feb;198(Pt 2):475–489. doi: 10.1242/jeb.198.2.475. [DOI] [PubMed] [Google Scholar]
- Waters D, Jones G. The peripheral auditory characteristics of noctuid moths: responses to the search-phase echolocation calls of bats. J Exp Biol. 1996;199(Pt 4):847–856. doi: 10.1242/jeb.199.4.847. [DOI] [PubMed] [Google Scholar]
- Waters D. The peripheral auditory characteristics of noctuid moths: information encoding and endogenous noise. J Exp Biol. 1996;199(Pt 4):857–868. doi: 10.1242/jeb.199.4.857. [DOI] [PubMed] [Google Scholar]