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

The spectral transmittance curves of individual families are plotted in Figure 3-2 (next page).
The spectacle scales of boas (Fig 3-2A) of the subfamily Boinae generally have high transmittance
throughout the visible and UV-A spectra, with mean λ50% of 319 nm. An exception is the green
anaconda with a significant reduction in transmittance beginning around 400 nm resulting in a λ50% of
361 nm. The one sample of an erycine boa, the rubber boa, exhibits a spectacle transmittance curve
with a gradual tapering beginning at greater wavelengths and a λ50% of 351 nm. A peak at 254 nm in
the UV-C is apparent.
Spectacle transmittance of the Pythonidae (Fig 3-2B) is similar to that of Boinae in that
transmittance remains high through the visible and UV-A spectra until cutting off abruptly in the far
UV-A (mean λ50% = 318 nm) and exhibit the same peak in the UV-C. The burmese python spectacle
does exhibit a gradual decrease in transmittance from 400 nm, but not to the same degree as in the
green anaconda.
The spectacle scale transmittance of Viperidae (Fig 3-2C) is similar in most respects to
Pythonidae and Boinae.
Elapids (Fig 3-2D), in contrast, exhibit cutoffs at higher wavelengths (mean λ50% = 367 nm).
Among the elapids, the snouted cobra has a particularly unusual spectacle transmittance profile with a
gradual reduction in transmittance apparent even above 500 nm. Its spectacle scale is in fact yellowish
in appearance. No appreciable transmittance occurs in the UV-C range.
The greatest intrafamilial diversity (perhaps on account of the greater number of samples) is
found within the colubrids (Fig 3-2E), in which λ50% varies from 312 to 406 nm, some species with a
transmittance peak in the UV-C, others without. While the spectacle scales of most species transmit
highly through the visual and UV-A spectra with relatively sharp cutoffs, those of Heterodon
platirhinos, the only sample of subfamily Xenodontinae (all others being of Colubrinae), attenuates
UV and even the shorter wavelengths of the visible spectrum. Among the Colubrinae, the spectacles of
most species present similar profiles but with shifted cutoff wavelengths. For example, those of
Lampropeltis cutoff further in the UV-A near 310 nm, whereas Masticophis flagellum, the various
species of Pituophis and several other genera have λ50% closer to 350 nm.
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