Geckos: The Animal Answer Guide

3. Gecko Colors

41 What colors are geckos? Geckos come in almost all possible colors. The most common colors are shades of brown, often light and dark in some combination of spots, blotches, stripes, reticulations, or bands. Gray, olive green, and black are also found. These drab colors serve geckos well, as they blend in well with the tree trunks, stones, and soil on which they are active. Many desert geckos have pastel earth tones to match the local sands. Especially beautiful reddish-browns or pinks are seen in some Knob-tailed Geckos, Nephrurus , and patterns including pale yellows are seen in Coleonyx variegatus, the Banded Gecko of the American southwest. Bright colors are mostly limited to diurnal geckos. Green coloration appears in the patterns of several species, such as the New Zealand Harlequin Gecko (Tukutuku rakiurae), but it is truly characteristic of two genera , the Green Geckos of New Zealand (Naultinus) and the Day Geckos of the Indian Ocean (Phelsuma). Bright green geckos are always diurnal, and they are usually active on vegetation. Geckos are capable of seeing blue and green, so these colors allow them to use visual signals to communicate with one another. At the same time, green coloration serves as excellent camou- flage against a background of vegetation, protecting geckos from birds and other visuallyoriented predators. Among the most striking colors seen on any gecko must be the electric blue of the Tanzanian Dwarf Day Gecko, Lygodactylus williamsi. Bright yellow or red heads are characteristic of males of species that use visual displays, like many Gonatodes. Colorful patches on the throat are typical of some highly vocal species like the Bell or Barking Gecko, Ptenopus garrulus. Chapter 3 Gecko Colors 42 Geckos: The Animal Answer Guide Gonatodes daudini, a small gecko from the Grenadines in the Lesser Antilles , has a striking combination of green and red in its color pattern and perhaps most spectacular of all is the aptly named Cnemaspis psychadelica, which has a yellow head, lavender body, and orange limbs, flanks, and tail. How geckos themselves perceive these colors is not entirely known. Although their eyes have retinal cones to detect blue and green wavelengths of light, the receptors most sensitive to reds are lacking. However, markings that we perceive as red may still be seen by geckos, but perhaps in the ultraviolet, for which geckos do have receptors. In addition to the rainbow of naturally occurring colors in geckos, there is a diversity of “abnormal” conditions of coloration that can occur and may even be favored in captive animals. An example of such a condition is albinism , or the absence of pigment. This condition yields white or pinkish animals , the latter due to the visibility of blood vessels through the pigmentless skin. In geckos amelanistic albinism, in which melanin is not produced but other pigments may be present, is most common. Other conditions include melanism—the overexpression of melanin (giving brown or black skin), hypomelanism —a reduction in the normal amount of melanin, and xanthism— yellowish skin due to high concentrations of xanthophores (see “What causes the different skin colors of geckos?” below). These exceptional colorations also occur in nature, but many are likely to be deleterious. Geckos exhibiting them probably rarely survive to maturity, as they may be more conspicuous to predators. In some geckos, especially the frequently kept Leopard Gecko, Eublepharis macularius, breeders have developed “designer morphs” that exhibit colors or color patterns not normally occurring in the wild. What causes the different skin colors of geckos? The skin of geckos and other lizards contains several types of pigmentcontaining cells called “chromatophores.” Deepest in the skin are “melanophores ,” which contain a brown pigment that yields a dark brown or black color. This is overlain by a layer of “iridophores” (also called “guanophores ”). These do not contain true pigments, but rather are filled with plates made of guanine that are reflective and produce iridescence when they are illuminated. Most superficial are yellow-pigment-containing xanthophores and cells containing red or orange carotenoids called erythrophores . The interplay between the different layers of chromatophores ultimately gives the gecko its final color. In drab-colored geckos, the melanophores are responsible for the browns or blacks one sees. In yellow species , the xanthophores dominate. Green coloration is an interesting case, because there are no green pigment cells in geckos. Instead, the combination of bluish reflected light from the iridophores and yellow from the 43...