Potential Spectral Tuning of the Tapetum Lucidum in a Broadly Distributed Ungulate.

The tapetum lucidum, a biological reflector system found in the eyes of many vertebrate species, enhances visual sensitivity in low light conditions by reflecting light back through the retina. The structure of the ungulate tapetum fibrosum is unique, and its reflectance varies temporally in reindeer (Rangifer tarandus). We used reflectance spectroscopy to characterize the white-tailed deer (Odocoileus virginianus) tapetum fibrosum and to determine if reflectance varies spatially across the species' range. Our results revealed spatial variation in tapetal coloration and reflectance across parts of the white-tailed deer's range, with populations displaying distinct spectral profiles. Deer in the northern populations of Missouri, Minnesota, and Indiana primarily possessed more short-wave-reflecting tapeta, whereas deer in the Georgia population exhibited more mid-wave-reflecting tapeta and the tapeta of Texas deer appeared intermediate in reflectance. Our findings suggest that tapetal reflectance in white-tailed deer may be influenced by ecological and environmental pressures that vary spatially. These results suggest that local variations in the spatial and temporal dynamics of the tapetum fibrosum in ungulates may be an adaptive trait.