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carpet python and western diamondback rattlesnake or predominantly acidic as in the spectacles of coachwhip snakes. The spectacle scale of hatchling reticulated pythons, representing the embryonic stratum corneum, contains a larger ß keratin not found in the adult and also have a much lower proportion of α keratin. It has been shown that the stratum corneum of hatchling snakes have a particularly thin mesos layer which nearly doubles in thickness after the first shed (Tu et al. 2002). This is thought to increase the efficacy of the water permeability barrier, which is not altogether necessary in the fluidic environment of the egg, but is absolutely essential upon hatching, especially in arid and semi-arid environments inhabited by the subject snakes of Tu et al.’s study (the California kingsnake, Lampropeltis getula). This increase in the the ratio of α:ß keratin would explain the low α keratin signal in the hatchling reticulated python. The difference in ß keratin complement is unclear. While the hatchling spectacle scale’s spectral transmission varies slightly after the first shed (see Chapter 3), it is not likely enough to affect vision. The biochemical difference may not be exclusive to the spectacle scale and may be again for permeability or for necessary mechanical properties of scales in ovo. 4.4.3 Keratins of Gecko Scales Gecko spectacle scales appear to be composed exclusively of α keratin. Being generally softer than ß keratin, this explains the relative ease with which the spectacles are damaged. And although this study does not conclusively relate biochemical composition with transparency, the absence of any ß keratin may conceivably be cause for the gecko spectacle’s exceptionally high spectral transmission. This absence also speaks to the modest need for mechanical protection of the eye in these arboreal animals. Unlike snakes that may use their heads to persistently penetrate substrates or that need to withstand potential retribution from large prey items, the eyes of arboreal geckos rarely encounter anything more harmful than a speck of dust or the occasional collision during their rapid and seemingly reckless locomotion. Nevertheless, any damage to the delicate surface risks damaging the underlying mesos layer. This layer is normally well shielded by the hard beta layer, but in the gecko 101
spectacle, this layer may be particularly vulnerable to damage that could impair its function as a permeability barrier (Landmann 1981). This of course presupposes that the gecko spectacle has a mesos layer, since no high resolution microscopic studies of the gecko spectacle have yet been published. Not all geckos are arboreal however. The burrowing gecko Ptenopus inhabits arid and sandy environments and is possibly the only spectacled species to have evolved mobile lids to cover the spectacle (Bellairs 1948). This condition has been difficult to explain as the spectacle has generally been considered the epitome of ocular shielding. If Ptenopus were to lack ß keratin in the spectacle like the geckos in this study, this may explain the need to evolve protection for the soft spectacle, particularly given its burrowing habits and the preponderance of abrasive sand in its environment. The integrity of the mesos layer will be especially important in this genus to minimize cutaneous water loss in the arid climate. An analysis of the keratin composition of Ptenopus’ spectacle would be especially valuable to better understand why it evolved novel eyelid analogues. The absence of ß keratin also implies the absence of oberhautchen or surface micro- ornamentation. These ultrastructural features are thought to be found on all reptilian scales (Hoge & Souza Santos 1953; Ruibal 1968; Chiasson & Lowe 1989; Chiasson et al. 1989), but given the absence of ß keratin in the gecko spectacle, the spectacle scale may have a completely different surface ultrastructure from any known scale. For example, mutant scaleless snakes that do not express ß keratin lack the more elaborate micro-ornamentation of scaled snakes, instead having an undulating surface of α keratin less than 200 nm thick, directly beneath which lies the mesos layer (Toni & Alibardi 2007b). Because of the potential relationship between scale surface ultrastructure and transparency (Campbell et al. 1999), an electron microscopic study of the gecko spectacle surface may be helpful to determine if the gecko spectacle’s high transmission can be accounted for by its lack of ß keratin oberhautchen. 102
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Investigations on the Reptilian Spe
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Abstract The eyes of snakes and mos
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Heritage Library, Smithsonian Libra
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2.2.1 Animals 36 2.2.2 Experimental
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List of Figures 1-1. The earliest a
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List of Tables 2-1. Durations of sp
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UV-A Ultraviolet A (315-400 nm) UV-
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“Il est de connaissance presque v
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1.1 Anatomy of the spectacle The si
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corneum, 2- an inner stratum corneu
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The two layers he described in the
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Figure 1-5. Illustration of the spe
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injected spectacles clearly shows t
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Figure 1-8. In vivo confocal micros
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1.1.3 The Spectacles of Geckos Most
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1.1.4 The Spectacles of Amphisbaeni
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Gymnophthalmus (spectacled tegus) a
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appreciates on observing the sadly
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hydration state (van Doorn, unpubl.
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1.5 Adaptive Significance of the Sp
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diurnally active in hot and dry hab
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of his argument hinges on the prese
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• In Chapter 3, findings on the v
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2.1 Introduction This introduction
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2.2 Methods & Materials The experim
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To allow for extended high-magnific
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At 30 minutes into the experiment,
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packages. All statistical analyses
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2.3 Results 2.3.1 Spectacle blood f
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Figure 2-7. Graph of two representa
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2.4 Discussion The purpose of this
Page 63 and 64: vascular changes were occurring onl
Page 65 and 66: Chapter 3, Spectral Transmission of
Page 67 and 68: like the cornea, may exhibit simila
Page 69 and 70: The scales of both the right and le
Page 71 and 72: Figure 3-1. Spectral transmittance
Page 73 and 74: % Transmittance % Transmission % Tr
Page 75 and 76: % % Transmittance Transmission % %
Page 77 and 78: λ 50% (nm) 420 400 380 360 340 320
Page 79 and 80: Thickness (!m) Figure 3-7. Plot of
Page 81 and 82: Family Spearmanʼs rho p Colubridae
Page 83 and 84: virtue of both being characteristic
Page 85 and 86: nocturnal (Brattstrom 1952; Klauber
Page 87 and 88: Another potential factor that may g
Page 89 and 90: Colubridae Colubrinae Elaphe taeniu
Page 91 and 92: Pythonidae Python sebae Rock Python
Page 93 and 94: 4.1 Introduction The reptilian spec
Page 95 and 96: thus be optimized to meet not only
Page 97 and 98: 4.2 Methods & Materials 4.2.1 Sampl
Page 99 and 100: for 15 minutes to remove all residu
Page 101 and 102: 4.3 Results 4.3.1 Keratins of Coach
Page 103 and 104: 24 kDa > 17 kDa > 12 kDa > S1 P1 V1
Page 105 and 106: 76 kDa > 52 kDa > 24 kDa > 17 kDa >
Page 107 and 108: 31 kDa > 24 kDa > 17 kDa > 12 kDa >
Page 109 and 110: 4.3.4 2D Electrophoretic Comparison
Page 111 and 112: kDa 76 - 52 - 38 - 31 - 24 - 17 - 1
Page 113: (2007a) have theorized that basic
Page 117 and 118: Chapter 5, Summary and Concluding R
Page 119 and 120: evaluations of the elastic modulus
Page 121 and 122: References Addison WHF, How HW. 192
Page 123 and 124: Berkley MA, Wakins DW. 1973. Gratin
Page 125 and 126: Chou BR, Hawryshyn CW. 1987. Spectr
Page 127 and 128: Fox RH, Edholm OG. 1963. Nervous co
Page 129 and 130: Hinkley JA, Savitsky AH, River G, G
Page 131 and 132: Lee P, Wang CC, Adamis AP. 1998. Oc
Page 133 and 134: Mautz WJ. 1982. Patterns of evapora
Page 135 and 136: Rice GE, Bradshaw SD. 1980. Changes
Page 137 and 138: Sillman AJ, Govardovskiĭ WI, Röhl
Page 139 and 140: Valentin G. 1879a. Ein Beitrag zur
Page 141 and 142: Appendix A One cycle of spectacle b
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