Superposition optics and the time of flight in onitine dung beetles |
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| Authors: | P McIntyre S Caveney |
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| Institution: | (1) School of Mathematics and Statistics, University College, The University of New South Wales, Australian Defence Force Academy, Canberra, ACT 2600, Australia Fax: +61-2-6268 8886, e-mail: p-mcintyre@adfa.edu.au, AU;(2) Department of Zoology, University of Western Ontario, London, Ontario, Canada N6A 5B7, CA |
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| Abstract: | Dung beetles fly to fresh dung, with vision essential for flight navigation. The daily period of flight varies among different
species: some beetles fly only in sunlight, others only when ambient light levels change rapidly during dusk or dawn and others
in the constant dark of night. Measurements of the optical properties of the lenses, eye geometry and photoreceptor dimensions
were used in a computer ray-tracing model to determine the optical performance of the superposition eyes of nine species of
onitine dung beetles. Eye sensitivity to light is determined mainly by body size, by the refractive-index parameters and size
of the crystalline cones, and by the photoreceptor dimensions. Based on the optics of the ommatidial lenses and absorption
of light in the retina, the most sensitive eyes, found in the crepuscular-nocturnal beetles, are 85 times or nearly two log
units more sensitive than the eyes of the diurnal beetles. Three possible criteria are considered to determine the best position
for the retina: maximum amount of light absorbed in the target rhabdom; maximum amount of light falling on the target rhabdom
(best focus); and maximum resolution. The structure and physiological optics of the superposition compound eyes of an onitine
dung beetle are matched to the range of light intensities at which it flies.
Accepted: 4 February 1998 |
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| Keywords: | Superposition eye Sensitivity Flight Optics Beetle |
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