Sound source localization in the tree cricket Oecanthus henryi
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1
Indian Institute of Science, Centre for Ecological Sciences, India
Localization of a sound source in three dimensions has been found to involve the presence of external auditory structures around the ear and computation in the central nervous system. Mammals have external pinnae and some birds such as owls have facial ruffs to aid in assessment of the vertical component of the sound source, essential for three-dimensional sound localization. The computation of sound source locations also involves a large number of neurons. In insect systems, the lack of a highly developed central nervous system and in most cases the absence of external auditory structures makes the problem even more interesting to study. Sound localization studies in insects have however mostly focused on localization in two dimensions, which has been shown to be achieved in crickets using a pressure difference ear. Oecanthus henryi, a tree cricket, which resides in bushes, provides us with an opportunity to study sound localization in three dimensions. This tree cricket lacks external auditory structures. Field observations showed that females were able to localize singing males who were at elevated or depressed positions with respect to them on the same or neighbouring bush. The accuracy of approach, given the constraints of the architecture of the plant, was also studied. Accuracy of approach was further investigated with lab experiments. Here, under more controlled conditions, the localization ability of the animals was explored separately in the horizontal and vertical planes. A closed loop paradigm was followed, with a spokes-on-a- wheel setup. The animals performed phonotaxis and were able to localize the speakers, though with some inaccuracy. Interestingly the carrier frequency of the male call changes with temperature in this system. To maintain the sender-receiver match females are broadly tuned to the entire range of natural calling frequencies at all temperatures. In two-choice frequency discrimination experiments, however, females showed a tendency to approach the higher frequency. This trend was most pronounced when females were given a choice between frequencies at the extreme ends of the male call carrier frequency distribution. In field crickets, it is known that changing the carrier frequency affects the localization capability of the animal. The tendency of tree cricket females to approach higher frequency calls may thus be due to their greater localizability. To test this, the accuracy of female phonotaxis at different frequencies is being studied.
Acknowledgements
We are grateful to the Ministry of Environment and Forests, Government of India for funding this project. M.B. is supported by a fellowship from Council of Scientific and Industrial Research, Government of India. We would also like to thank Manjunath K. for help with the setup and experiments, Ashoka N., Narsimhamurthy U.A. for animal collection and Diptarup Nandi and Rittik Deb for valuable discussions.
Keywords:
carrier frequency,
phonotaxis,
sound source localization in three dimension,
tree cicket
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Sensory: Audition
Citation:
Bhattacharya
M and
Balakrishnan
R
(2012). Sound source localization in the tree cricket Oecanthus henryi.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00138
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Received:
27 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Rohini Balakrishnan, Indian Institute of Science, Centre for Ecological Sciences, Bangalore, Karnataka, 560012, India, rohini@ces.iisc.ernet.in