How temperature affects locust hearing
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1
Humboldt-Universität zu Berlin, Department of Biology, Germany
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2
University of Strathclyde, Department of Electronic and Electrical Engineering, United Kingdom
Poikilothermic (ectothermic) animals are affected by variations in environmental temperature, as their body temperature fluctuates with ambient conditions. Their sensory systems need to function effectively over a wide range of temperatures as sudden environmental changes of up to 10°C or more are not uncommon. For species and mate recognition, many acoustically communicating insects rely on decoding the temporal characteristics of conspecific calls. Temperature will affect both sender and receiver of acoustic signals by influencing basic properties such as spike rate, conduction velocity, and spike amplitude of neurons and muscle cells. Thus, the ability to cope with changes in temperature is crucial for mate finding in those species.
In the present study we investigate the performance of auditory receptor neurons and the tympanal membrane of Locusta migratoria in relation to temperature changes. In locusts, the tympanal membrane is located laterally on the first abdominal segment. Receptor neurons are attached to the tympanal membrane and, via their axons, deliver afferent signals to the metathoracic ganglion. There the first processing steps take place before further transmission to the brain. We recorded intracellularly from receptor neurons within the metathoracic ganglion; each receptor was recorded at 20°C and 30°C. From the recordings, spike rate vs. intensity curves were obtained and temperature coefficients (Q10) were determined. Additionally, the movement of the tympanal membrane was monitored at 6 representative locations, also at 20°C and 30°C, using a Laser-Doppler-vibrometer.
Remarkably, a 10°C change in temperature had little effect on the receptor’s spike rate. The spike frequency changes corresponded to a Q10 of only 1.24, which is much lower than the expected value of ~2, as typical for various metabolic and physiological rates. We then tested whether the movement of the tympanal membrane could account for the increase in spike rate with rising temperature. We found a significantly enhanced movement in the hotter condition. Amplitude of the tympanal membrane exhibited a similar variation with changing temperatures as receptor spike rate, with a mean Q10 of 1.22.
We conclude that temperature changes have only little effect on the spike rates of locust receptor neurons. As spike rate depends on the movement of the tympanum, its rise is at least to some extent caused by the increased movement of the tympanal membrane at higher temperature. The Q10 values of spike rate and tympanal membrane movement are similar, suggesting that locusts are affected by temperature changes already at the very periphery of the auditory pathway. Robust encoding of acoustic signals by almost temperature independent receptor neurons might enable the locusts to reliably identify sounds (e.g. approaching predators) in spite of changes of their body temperature.
Acknowledgements
Supported by DFG (SFB 618)
Keywords:
Locust,
receptor neurons,
temperature,
tympanal membrane
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:
Eberhard
MJ,
Gordon
SD,
Windmill
J and
Ronacher
B
(2012). How temperature affects locust hearing.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00111
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Received:
25 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Monika J Eberhard, Humboldt-Universität zu Berlin, Department of Biology, Berlin, 10115, Germany, monika.eberhard@biologie.hu-berlin.de