Visual pigments, cone oil droplets, ocular media and predicted spectral sensitivity in the domestic turkey (Meleagris gallopavo)

A microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey (Meleagris is gallopavo) revealed the presence of five different types of vitamin A(1)-based visual pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive visual pigment (wavelength of maximum absorbance, lamb da(max), 504 nm). Four different types of single cone contained visual pigm ent maximally sensitive to wavelengths in either the long (LWS, lambda(max) 564 nm), medium (MWS, lambda(max) 505 nm), short (SWS, lambda(max) 460 nm) or violet (VS, lambda(max) 420 nm) spectral ranges. The LWS, MWS and SWS s ingle cones contained pigmented oil droplets with cut-off wavelengths (lamb da(cut)) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the princip al and accessory members of which contained the LWS cone visual pigment. Th e principal member contained an oil droplet with a lambda(cut) at 436 nm. N o oil droplet was observed in the accessory member. The use of a glycerol-b ased cell mountant, which reduced wavelength dependent measurement artefact s in the microspectrophotometric measurements, is described. Predictions of cone effective spectral sensitivity, incorporating measurements of the spe ctral transmission of the ocular media, suggest that turkeys have considera ble sensitivity to wavelengths in the ultraviolet-A (UV-A, 315-400 nm) spec tral range. This has implications for both the visual ecology of wild birds and the welfare of intensively farmed individuals. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.