Observations on the ultrastructure and distribution of chromatophores in the skin of chelonians

Abstract

Alibardi, L. 2011. Observations on the ultrastructure and distribution of chromatophores in the skin of chelonians. —Acta Zoologica (Stockholm) 00:1–11. The cytology and distribution of chromatophores responsible for skin pigmentation in chelonians is analyzed. Epidermal melanocytes are involved in the formation of dark spots or stripes in growing shelled and non‐shelled skin. Melanocytes rest in the basal layer of the epidermis and transfer melanosomes into keratinocytes during epidermal growth. Dermal melanophores and other chromatophores instead remain in the dermis and form the gray background of the skin. When dermal melanophores condense, they give origin to the dense spots or stripes in areas where no epidermal melanocytes are present. In the latter case, the epidermis and the corneous layer are transparent and reveal the dermal distribution of melanophores and other chromatophores underneath. As a result of this basic process of distribution of pigment cells, the dark areas visible in scales can have a double origin (epidermal and dermal) or a single origin (epidermal or dermal). Xanthophores, lipophores, and a cell containing both pterinosomes and lipid droplets are sparse in the loose dermis while iridophores are rarely seen in the skin of chelonians analyzed in the present study. Xanthophores and lipophores contribute to form the pale, yellow or oranges hues present among the dark areas of the skin in turtles.

Spectral reflectance and substrate color-induced melanization in immature and adult Midland painted turtles (Chrysemys picta marginata)

“…However, throughout most of its range, aquatic predators that would be large enough to consume adult C. picta are likely to be rare and so the adaptive value of substrate color convergence may be rather low for adults. Substrate color-induced melanization in adults may be a simple hormonal reflex that involves MSH or epinephrine (Alibardi, 2013) that may not have survival consequences for adults.…”

“…Since epidermal melanocytes are scarce or absent in yellow or red stripe regions (Alibardi, 2013), color change in those areas would occur through changes in the content and distribution of melanin within the dermal melanophores (Woolley, 1957). It remains unclear, however, if darkening or lightening of yellow or red stripes or blotches would enhance the degree of background matching.…”

“…blotches of the marginal scutes) of turtles reared on black substrates would be expected to be dark as the result of melanocyte and melanophore activity (Alibardi, 2013;Rowe et al, 2013b). The red, orange, or yellow regions of the skin are determined by carotenoids or pterins in xanthophores and lipophores (Alibardi, 2013). Since red or yellow regions contain some dermal melanophores but few melanocytes (Alibardi, 2013), we did not expect that turtles reared on a black substrate would be substantially darker than in individuals reared on a white substrate.…”

“…Relative to turtles reared on a white substrate, ground colors of the soft skin, carapace, and relatively dark markings of the shell (e.g. blotches of the marginal scutes) of turtles reared on black substrates would be expected to be dark as the result of melanocyte and melanophore activity (Alibardi, 2013;Rowe et al, 2013b). The red, orange, or yellow regions of the skin are determined by carotenoids or pterins in xanthophores and lipophores (Alibardi, 2013).…”

“…The red, orange, or yellow regions of the skin are determined by carotenoids or pterins in xanthophores and lipophores (Alibardi, 2013). Since red or yellow regions contain some dermal melanophores but few melanocytes (Alibardi, 2013), we did not expect that turtles reared on a black substrate would be substantially darker than in individuals reared on a white substrate.…”