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Lecture 2

Lecture 2 Includes structure of the cricket


Department
Biology
Course Code
BIO325H5
Professor
Glenn Morris
Lecture
2

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Lecture 2:
Katydids are insects in the order orthoptera, close relatives of crickets
males broadcast an acoustic signal to attract females for mating
high species diversity, >7000 spp described
calling songs made by males rubbing their forewings together: usually left over right, so not
bilaterally symmetrical
ears located on proximal end of fore tibiae
structures relating to stridulation produced by sexual not natural selection
reproductive success is because of the choice of the female (sexual selection)
What does the whit spot on its face?
Light sensitive organ cell
Scudderia curvicauda species offer a good example of forewings (and hind wings) functional in both
flight and stridulation
macropterous: full wings exceed body length
Ultrasonic starts at 20 kHz
no relation between tooth rate and carrier between tooth rate and sound radiator’s resonant
frequency
sound that is produced is a broad space of energy
Crickets:
calling songs are made by males rubbing their forewings together: usually right over left with
bilateral wing symmetry: resonant stridulation
they also listen with ears located on their fore tibiae
most species of cricket produce songs with a pure-tone carrier frequency (high Q) near 4.5 kHz
wavelength produced is 7 cm which is larger than a typical cricket
Oecanthus is a genus of tree crickets; this species produces a steady trill by successive to-fro movements
of the tegmina: sound produced only on closure: high Q carrier: one dominant frequency
Higher frequency travels and loses its energy therefore going a shorter distance
for most katydid males the farther their calling signal reaches the better: long range is good
the adaptiveness of these very high frequency carriers may lie in selection for reduced range:
ultrasonics lose their energy more rapidly so the range of a 108 or 130 kHz signal is severely reduced
(by sound attenuation). The male may be benefitting from the restricted range by avoiding giving his
location away to eavesdropping predators such as bats
dogs have their pinnae modified by artificial selection. Wolf on the other hand has their pinnae
functional.
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