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

escape behaviours or also during predation? Is it specific to the spectacle or a manifestation of a
generalized sympathetic response of the whole integument? How to reconcile this mechanism with
thermoregulatory mechanisms? As with all scientific findings, the questions raised in the aftermath are
numerous.
Turning then to the transparency of the scale, another trait unique to the reptilian spectacle, it
was asked how this optical keratinized structure might tune the spectrum of incident light to suit the
animal’s visual needs and possibly its need for protection again damaging radiation. After all, the
spectacle scale is the outermost layer and the first encountered by incoming radiation. Only in the
snouted cobra, Naja annulifera, does the yellow spectacle scale block sufficient short-wavelength
radiation to convincingly be considered a UV filter, but the yellow filter may have evolved instead (or
in addition) to increase contrast by blocking shorter wavelengths most prone to scattering or dispersion
(Sivak 1982; Sivak & Mandelman 1982). In other species, the role of the spectacle scale in UV
protection or contrast enhancement remains ambiguous (eg. the coachwhip’s sharp cutoff at 350 nm) or
is completely absent (eg. pythonids, viperids, Lampropeltis). The diversity of transmission profiles and
cutoff wavelengths and the correlation of these with taxonomic family suggest that cutoff wavelengths
may not be adaptive for many species, but may instead reflect some other characteristic of the
spectacle which may be adaptive. Scanning electron microscopy of the surface of the spectacle scale to
compare ultrastructural features between species with differing transmission profiles may be helpful in
clarifying the contribution of oberhautchen to spectral transmittance.
One such characteristic is the thickness of the spectacle scale. That thickness and λ50% were
correlated only in Colubridae and that thickness varied between families points to the potentially
multiple roles played by the spectacle and especially to the wide degree of mechanical protection that
it affords. The question remains of why colubrid spectacle scales are so much thicker on average than
those of pythonids, boids and viperids. As discussed in Chapter 3, this may reflect the vulnerability of
the colubrid eye during rapid locomotion or to predators and retaliating prey. The material properties of
snake scales have recently come under scrutiny (Klein et al. 2010; Klein and Gorb 2012) with
105