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

3.4 Discussion
The purpose of this study was to determine if variation exists in the transmittance spectra of spectacle
scales and, if so, whether evolutionary relationships or ecological factors could account for any
differences. Significant differences were indeed found between families and unique spectra were
observed in a few species, attesting to the diversity of which the spectacle is capable and its
significance in tuning the spectrum of incident light.
3.4.1 Differences Between Families in Spectacle Scale Transmittance Spectra
Most spectra exhibit high transmittance in the visible and near UV-A ranges but begin to differ in the
middle UV-A as evidenced by the variation in cutoff wavelengths. The Colubridae differ markedly in
spectacle scale transmittance from Pythonidae and Viperidae, as well as most Boidae other than the
green anaconda (Eunectes murinus) and rubber boa (Charina bottae). The high λ50% of Elapidae seems
to parallel that of colubrids.
A point should be made that most of the samples within any given family were not only of a
specific subfamily, but also from a restricted number of genera, somewhat skewing the representation.
Single species were available from other subfamilies, and in some cases, the spectacle scales of these
presented rather different transmittance spectra. The xenodontine hognose snake, Heterodon
platirhinos, showed the highest λ50% (mean λ50% = 382 nm, Max = 406 nm) among all colubrids,
blocking much of the UV-A spectrum. Among the Boidae, the erycine rubber boa (Charina bottae) has
a spectacle scale with a high λ50% (351 nm), second only to that of the green anaconda (λ50% = 361 nm)
within the Boidae. The spectacle scale transmittance of the viperine Gaboon viper, Bitis gabonica (λ50%
= 331 nm), also is higher than that of crotaline vipers (mean λ50% = 316 nm). That such differences
were found in these samples warrants further investigation to determine if they are representative of
their respective subfamilies.
The λ50% of spectacle scales is correlated with their thickness, particularly in colubrids,
although it’s unclear if thickness is the cause of and λ50% the effect. The association may be indirect by
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