Conspicuousness of Dickerson's collared lizard (Crotaphytus dickersonae) through the eyes of conspecifics and predators

Abstract

Selection should favour coloration in organisms that is more conspicuous to their own visual system than to those of their predators or prey. We tested this prediction in Dickerson's collared lizard (Crotaphytus dickersonae), a sexually dichromatic desert reptile that preys on insects and smaller lizard species, and which in turn is prey for birds and snakes. We modelled the spectral sensitivities of the lizards and their avian and snake predators, and compared the conspicuousness of the lizards' entire colour patterns with each class of viewers. Almost all comparisons involving females strongly supported our prediction for greater chromatic and brightness conspicuousness against local terrestrial visual backgrounds to their own modelled visual system than to those of avian and snake predators. Males, in contrast, exhibited far fewer cases of greater conspicuousness to their own visual system than to those of their predators. Our own perception of spectral similarity between blue C. dickersonae males and a local nonterrestrial visual background (i.e. the Sea of Cortéz) prompted a further investigation. We compared sea (and sky) radiance with dorsum radiance of C. dickersonae males and with males from two distantly-related Crotaphytus collaris populations in which males possess blue bodies. In all three visual models, C. dickersonae males exhibited significantly lower chromatic contrast with the sea (and sky) than did their noncoastal, blue-bodied congeners. Among potential explanations, the blue body coloration that is unique to male C. dickersonae may offset, if only slightly, the cost of visibility to predators (and to prey) through reduced contrast against the extensive, local, nonterrestrial blue backgrounds of the sea and sky.

Ultraviolet vision in lacertid lizards: evidence from retinal structure, eye transmittance, SWS1 visual pigment genes, and behaviour

“…2E,F). Based on differences in cutoff wavelengths obtained by the use of microscopy filters (Table 3) and a comparison with previous work with other lizard species, we suggest that T, C, LY and Y oil droplet types are part of the UVS, SS, MS and LS photoreceptors, respectively (Fleishman et al, 1993;Loew et al, 2002;Bowmaker et al, 2005;Macedonia et al, 2009). …”

“…transparent small oil droplets) that allows the transmission of UV wavelengths and suggests the existence of a population of UVS photoreceptors. Loew et al, 2002) and snakes (Sillman et al, 1997;Sillman et al, 1999;Sillman et al, 2001;Macedonia et al, 2009)], the shortsensitive photoreceptor of lacertids is likely of the UVS type. Moreover, sequences of the SWS1 opsin gene strongly suggest that this gene expresses a UVS-type opsin instead of the VS type.…”

“…Goldsmith et al, 1984;Bailes et al, 2006). The evidence supporting this oil droplet-cone type specificity is especially strong in birds, but recent research supports a similar specificity for diurnal lizards (Loew et al, 2002;Bowmaker et al, 2005;Macedonia et al, 2009;Fleishman et al, 2011).…”

“…The retinas of diurnal lizards also contain double cones, but their role in colour vision has not been established (Loew et al, 2002;Fleishman et al, 2011). The peak sensitivity of the UVS photoreceptor ranges from 359 nm in Crotaphytus dickersonae to 383 nm in Chamaleo dilepis (Fleishman et al, 1993;Fleishman et al, 1997;Loew, 1994;Ellingson et al, 1995;Loew et al, 1996;Loew et al, 2002;Bowmaker et al, 2005;Macedonia et al, 2009;Fleishman et al, 2011). Unfortunately, efforts so far have been focused on a few species belonging to Iguania and the extremely variable Gekkota and Serpentes.…”

High sensitivity to short wavelengths in a lizard and implications for understanding the evolution of visual systems in lizards

“…All Iguania thus far studied show the same basic pattern of retinal photoreceptors. All appear to have tetrachromatic colour vision based on four classes of cone pigments with similar peak absorption wavelengths (l max ) [7,8,27,28]. Among the Gekotta, both nocturnal and diurnal forms have only three classes of photoreceptors (referred to as rods in the nocturnal forms, and cones in the diurnal).…”