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Navadni obad (Tabanus bromius, Linnaeus 1758) uporablja vid za pomembne vedenjske naloge. Oba spola iščeta vodo, ki je ključna za razmnoževanje vrste in rastline, s katerih pijeta sokove. Poleg tega samci uporabljajo vid za zaznavo samic na nebu, samice pa zaznavajo plen na kompleksnem zelenem ozadju. Sestavljene oči odlikuje izrazit spolni dimorfizem. Raziskali smo anatomske in funkcionalne lastnosti fotoreceptorjev v mrežnici obeh spolov. Uporabili smo svetlobno in elektronsko mikroskopijo ter elektrofiziološke meritve. Akutni coni pri obeh spolih sta visoko specializirani za detekcijo potencialnega partnerja oz. plena. Pri samcih je akutna cona (t.i. zalezovalnik, angl. love spot) nameščena dorzofrontalno, pri samicah pa frontalno. Premer faset v akutni coni je pri samcih ≤ 50 µm, pri samicah pa ≤ 40 µm. Interomatidijski kot v akutni coni obeh spolov znaša ~1,1°. Rabdom je pri samcih dolg 350 µm, pri samicah 250 µm. Pri samicah in v ventralni mrežnici samcev sta centralni celici R7 in R8 optično sklopljeni v centralno rabdomero. Pri samcih je v zalezovalniku distalna celica (R7) pretvorjena v periferno, proksimalna celica (R8) pa je reducirana. R1-7 samcev imajo izboljšano razmerje signal/šum, razširjeno dinamično delovno območje receptorskega potenciala in vrh spektralne občutljivosti v UV in modrem (max=350,450 nm). Drugje imajo R1-6 vrh občutljivosti v zelenem (max=520 nm). Stopitvene frekvence v akutnih conah nad 30 °C dosegajo 300 Hz (samci) oz. 450 Hz (samice). Informacijska kapaciteta samčjih perifernih receptorjev je dvakrat višja kot pri samičjih (400 proti 200 bitov/s). Samci imajo v akutni coni razvit akromatski vid, optimiziran na zaznavo minimalnih zatemnitev. Njihovi fotoreceptorji dosegajo visoko informacijsko kapaciteto tako na račun izboljšanega razmerja signal/šum, kot tudi pasovne širine odziva. 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. |
