Albinism in the Thick-headed Groundsnake, Atractus crassicaudatus (Squamata: Dipsadidae)

S ome species of snakes exhibit substantial variability in coloration that can be influenced by environmental conditions and/or genetics (Solórzano 2011;Montandon et al. 2025).Such color variation can play a crucial role in individual fitness, mediating interactions with both the environment and other organisms (Bechtel 1994).Polychromatism in snakes frequently is associated with ecological strategies such as camouflage and aposematism, with coloration ranging from cryptic hues such as black, brown, gray, tan, or green for concealment, to vivid patterns incorporating red, blue, or yellow that often are used as warning signals (Cox and Davis-Rabosky 2023).Although chromatophores are directly responsible for color patterns, mechanisms underlying coloration vary by species.In Eastern Cornsnakes (Pantherophis guttatus), coloration is strongly linked to the CLCN2 gene, producing orange, red, and brown blotches or stripes (Montandon et al. 2025).In contrast, coloration of Yellow-bellied Sea Snakes (Hydrophis platurus) might be ecologically modulated by water temperatures and oxygen availability, resulting in color patterns ranging from bright yellow to black (Solórzano 2011).Among the most striking color variants is albinism, a condition characterized by a complete absence of melanin, with albino snakes typically displaying pale coloration, including white, pale yellow, or even bright orange scales, while retaining iridophores and xanthophores, which are not affected by the mutation (Bechtel 1994;Fertl and Rosel 2018).Although the ecological role of albinism in snakes remains unclear, it does impair camouflage, increase sensitivity to sunlight, reduce reproductive success, and affect thermoregulation (Sazima and Di Bernardo 1991;Bechtel 1994).Albinism has been reported in several dipsadid snakes, including Conopsis nasus, Dipsas neuwiedi, Liophis miliaris, and Phalotris lemniscatus, all of which are fossorial or nocturnal (Sazima and Di Bernardo 1991; Silva et al. 2010; Diesel-Abegg et al. 2015; Berriozabal-Islas et al. 2022).Among cryptic, fossorial, and predominantly nocturnal snakes, the genus Atractus stands out not only for being among the most species-rich snake genera but also for its remarkable ecological and biogeographic breadth.Several species inhabiting the tropical Andes occur at elevations exceeding 2,000 m asl, an unusual trait among fossorial colubroids (Arteaga et al. 2022).Species of Atractus are typically fossorial or semi-fossorial, occupying leaf litter and superficial soil layers, and exhibit extensive morphological diversity, with bodies ranging from small, slender species to comparatively robust taxa exceed-Albinism in the Thick-headed Groundsnake, Atractus crassicaudatus (Squamata: Dipsadidae)