Chapter 1, The Reptilian Spectacle - UWSpace - University of ...

Chapter 5, Summary and Concluding Remarks
Though minuscule in area compared with the whole of the integument, the reptilian spectacle presents
numerous specializations of the skin to permit acute vision while still maintaining the integument’s
protective role. The research presented in this thesis covered two such specializations: (1) the vascular
dynamics that act to minimize the effect of the spectacle vasculature in the visual field, and (2) the
transparent scale that has a different composition than scales elsewhere on the integument and in some
cases exhibits potentially adaptive transmittance spectra.
The spectacle vasculature presents a unique visual problem in that no other known vertebrate
(manatees excepted; Harper et al. 2005) has blood vessels in the optically transmissive portions of the
eye other than the retina. What’s more, the eyes of spectacled reptiles rotate freely beneath their
spectacles, causing shifts in the location of the vessels within the visual field, which would interfere
with adaptation (Troxler 1804; Lettvin et al. 1968). Lüdicke’s (1969) finding of the asymmetry of
Ahaetulla nasuta’s spectacle vasculature and Mead’s (1976) finding of the vessel walls being
transparent, just as are retinal blood vessel walls (Martin 2009), further reinforce the supposition that
the spectacle vessels can be detrimental to vision (from an unspectacled species’ perspective) and hint
at the evolutionary tweaking that’s taken place to maximize spectacled animals’ visual clarity.
Cutaneous vasculature is especially apt at regulating flow via vasomotor mechanisms (Fredericq 1882;
Hertzman 1959; Fox and Edholm 1963; Kellogg Jr. 2006), leading one to wonder if the spectacle blood
vessels may react to endogenous or exogenous stimuli and if such stimuli were to induce constriction
of the vessels, all visual problems might be solved (for a time). The results presented in Chapter 2
demonstrated that a neural mechanism does exist to enable spectacle vessels to constrict when a
sympathetic response is incurred. The potential for future research is certainly not lacking, as the
results raise several interesting questions on the mechanism involved and its prevalence among
spectacled species. Is the mechanism observed in snakes comparable across species, whether highly
visual (eg. A. nasuta) or not (eg. blind snakes)? Is the mechanism present in species with windowed
eyelids? Is the mechanism engaged only when faced by a perceived threat to facilitate defensive and
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