Lens and cornea limit UV vision of birds – a phylogenetic perspective

Abstract

Most vertebrates have UV-sensitive vision, but the UV-sensitivity of their eyes is limited by the transmittance of the ocular media, and the specific contribution of the different media (cornea, lens) has remained unclear. Here we describe the transmittance of all ocular media (OMT), as well as that of lenses and corneas of birds. For 66 species belonging to 18 orders, the wavelength at which 50% of light is transmitted through the ocular media to the retina (λT0.5) ranges from 310 to 398 nm. Low λT0.5 corresponds to more UV-light transmitted. Corneal λT0.5 varies only between 300 and 345 nm, whereas lens λT0.5 values are more variable (between 315 and 400 nm) and tend to be the limiting factor, determining OMT in the majority of species. OMT λT0.5 is positively correlated with eye size, but λT0.5 of corneas and lenses are not correlated with their thickness when controlled for phylogeny. Corneal and lens transmittances do not differ between birds with UV- and violet-sensitive SWS1 opsin when controlling for eye size and phylogeny. Phylogenetic relatedness is a strong predictor of OMT, and ancestral state reconstructions suggest that from ancestral intermediate OMT, highly UV-transparent ocular media (low λT0.5) evolved at least five times in our sample of birds. Some birds have evolved in the opposite direction towards a more UV-opaque lens, possibly due to pigmentation, likely to mitigate UV-damage or reduce chromatic aberration.

Ecology drives patterns of spectral transmission in the ocular lenses of frogs and salamanders

“…Shortwave‐absorbing ocular filters are found in the lenses of diverse species across all major vertebrate groups examined, including fishes (Douglas & McGuigan, 1989; Siebeck & Marshall, 2000, 2001, 2007; Thorpe et al., 1993), humans (Kessel et al., 2010) and other mammals (Douglas & Jeffery, 2014), reptiles (Gower et al., 2019; Simões et al., 2016), birds (Lind et al., 2014; Olsson et al., 2021) and frogs (Yovanovich et al., 2019, 2020). However, we currently have little understanding of the forces driving the evolution of lens pigmentation in any group, and only recently have studies started to use phylogenetic comparative methods to investigate the evolution of this trait (e.g.…”

“…However, we currently have little understanding of the forces driving the evolution of lens pigmentation in any group, and only recently have studies started to use phylogenetic comparative methods to investigate the evolution of this trait (e.g. Olsson et al., 2021; Yovanovich et al., 2020). To our knowledge, no study has found evidence for correlated evolution of lens transmission and any aspect of ecology.…”

Underwater visibility constrains the foraging behaviour of a diving pelagic seabird

“…This could occur through mixing at ocean front systems for instance [ 54 ], as sea-surface temperature gradients at frontal mixing zones can create dense cloud cover through accelerated atmospheric convection [ 55 ]. Manx shearwaters possess either violet sensitive (VS) or ultraviolet sensitive vision (UVS) [ 56 , 57 ]. Clouds don't attenuate these shorter wavelengths of light to the same degree as longer wavelengths in the visible spectrum [ 58 ], so complete cloud cover may not limit availability of Manx shearwater's visible spectra as much as we might expect.…”

Selecting auditory alerting stimuli for eagles on the basis of auditory evoked potentials

“…Using sensory physiological studies to determine candidate stimuli for target species is an approach that allows for selection of targeted sensory stimuli and at a minimum helps to avoid implementing stimuli that cannot be perceived by the target animals ( Lim et al , 2008 ; Blumstein and Fernández-Juricic, 2010 ). For example, visual physiology and genetic research has shown that falcon and accipiter raptor eyes, including golden eagle eyes, filter out ultraviolet light and/or do not have ultraviolet-sensitive photoreceptors ( Doyle et al , 2014 ; Lind et al , 2014 ; Olsson et al , 2021 ), therefore making it unlikely that raptors would respond to ultraviolet light stimuli or deterrents ( Hunt et al , 2015 ; May et al , 2017 ). Similarly, we found sensory differences between the bald and golden eagles and between different types of sounds in noisy backgrounds, which collectively suggest that sound selection is important for development of effective alerting stimuli.…”