The band-eyed brown horsefly (Tabanus bromius, Linnaeus 1758) uses vision for important behavioral tasks. Both sexes use it to locate bodies of water, which are crucial for the reproduction and plants with which they feed. The males use vision to locate females, the females use it to locate their prey. The eyes are sexually dimorphic. We have investigated the anatomical and functional aspects of the retina of both sexes. We used light and electron microscopy and electrophysiological measurements. The acute zones of both sexes are highly specialised for their specific tasks – location of a potential mate or prey. In males, the acute zone or the so called love spot is located in the dorsofrontal region of the eye, in females in the frontal region. In the male acute zone, the diameter of the facets is ≤50 µm, in females ≤40 µm. The interommatidial angles in the acute zones of both sexes are ~1,1°. The length of the open rhabdom is 350 µm in males and 250 µm in females. In females, the central photoreceptors are optically coupled into central rhabdomere. In males, the situation is similar in the ventral region. In the love spot, the R7 receptor is functionally transformed into a peripheral receptor. In this case, the proximal cell R8 is greatly reduced. R1-7 in the acute zone of males have a superior SNR, a wider dynamic range of the receptor potential and a peak in the spectral sensitivity in blue and UV (max=350,450 nm). In R1-6 of the ventral region, the peak in the spectral sensitivity remains in the green part of the spectrum, similar to females (max=520 nm). The flicker fusion frequencies are ≤300 Hz in male and ≤450 Hz in female acute zones, at T>30 °C. The information capacity of the male peripheral photoreceptors is twice as high, as in females (400 vs. 200 bits/s). Male vision in the love spot is achromatic, insensitive to polarised light and adapted fort the detection of minimal intensity contrasts. Their photoreceptors reach a high information capacity on the account of a higher SNR, and also due to a broader frequency coding bandwidth.
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