Avoiding Predators 1

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Published on 16 Mar 2011
School
UTSC
Department
Neuroscience
Course
NROC34H3
Professor
Steering Responses of Flying Crickets to Sound and Ultrasound: Mate Attraction and Predator Avoidance
Dangerous Sounds: Avoiding Predators
Crickets can evade bats by acoustic detection through negative phonotaxis
Direction of response is dependent of carrier frequency of song females turned toward
calling song when it was play at carrier frequencies from 3-9kHz but turned away from the
same song pattern played at carrier frequencies from 30-70kHz
Purpose of Paper: To describe the role of carrier frequency (pitch) in the phonotactic behaviour of crickets
At frequencies similar to those produced by calling males, crickets performed steering movements
toward the sound source
At higher frequencies, such as those produced by hunting bats, they steered away from the sound
source
A.Steering Behaviour
In the absence of acoustic stimulation, most crickets assumed a straight and symmetrical
flight posture, with the abdomen and metathoracic legs extended directly backwards
When calling song (5kHz) was played on crickets left, its abdominal positioned to the left
(turns left)
When calling song (40Hz) was played on crickets left, its abdominal positioned to the right
(turns right)
B.Frequency Sensitivity
When the behavioural thresholds of 12 animals were measured over the range from 3kHz to
100kHz, each animal exhibited two sensitivity peaks:
oMost sensitive between 4.5 and 5.5kHz in the range between 3-20kHz
oMost sensitive between 35-80kHz when above 20kHz
oSensitivity was greatest in the lower of these two frequency ranges
Sensitivity of the crickets ear varies sharply as a function of sound frequency
C.Direction of Response
The direction of turning movements, whether toward (positive) or away (negative) from the
sound source, depends on carrier frequency of the sound
Ambiguous cases: cricket gives bimodal response where it first steered in one direction then
the other
From 3-9kHz: responses were predominantly positive (towards the source)
From 10-25kHz: response signs changed systematically from positive to negative
From 30-70kHz: responses were mostly negative (away from source)
Above 70kHz: positive responses were again evident (towards source)
D.Sensory Modality
Directional steering to sound stimulation is mediated by sense organs on front legs when
both front legs were removed (hence both ears), directional responses to sound disappeared
Inputs from both legs are involved in determining response direction
oWhen one front leg was removed, the animal steered toward the side with the intact
leg when low frequency sounds were played and steered away from the side with the
intact leg when high frequency sound was played
Each front leg bears two tympanic membranes: a large posterior one and a smaller anterior
one
oPosterior tympanum provides the major input for steering responses to both low and
high frequency sounds
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