Two records of xanthism in Corallus hortulana (Serpentes: Boidae) in Bolivia with comments on the yellow, patternless morphotype

ABSTRACT Snakes display a wide range of skin colors and patterns, acting in ecological, behavioral, and physiological roles. Xanthism has been reported in numerous snake species, including many neotropical taxa. Corallus hortulana is a polychromatic species widely distributed throughout South America. Yellow, patternless individuals, while rare, have been recognized as within the species’ polychromatic range. We report the first yellow, patternless specimens of Corallus hortulana collected in Bolivia and discuss whether these individuals fit the criteria of xanthism.

Common aberrant color patterns of hyperpigmentation and/or hypopigmentation in snake species include albinism, characterized by total (red eyes and completely pigmentless body) to partial absence of pigmentation; leucism, defined by normally pigmented eyes and partially or totally pigmentless body; xanthism and erythrism characterized by the overabundance of yellow or red pigment, respectively; and melanism, an overexpression of the black pigment melanin (Harris 1970;Bechtel 1978Bechtel , 1995;;Dyrkacz 1981).Due to ambiguity in the literature, Borteiro et al. (2021) recently redefined and clarified the criteria and terminology used to describe aberrant color patterns in wild snakes.
Amazonian populations of C. hortulana are highly polychromatic, displaying a range of colors and patterns (Stafford and Henderson 1996;Henderson 1993Henderson , 1997Henderson , 2002;;Duarte et al. 2015).Polychromatism in snakes has been suggested to be associated with several environmental, geographical, behavioral, and genetic variables (Henderson 1997;Farallo and Forstner 2012;Pizzatto and Dubey 2012;Duarte et al. 2015).In C. hortulana, the polychromatism has been described and categorized into character states or morphotypes [see Henderson (1997) and Duarte et al. (2015) for more details].Interestingly, there is only one record of an aberrant color pattern (leucism) in C. hortulana, documented from a specimen in French Guiana (Fernandes et al. 2022), which does not fit within the designated morphotypes of Henderson (1997) or Duarte et al. (2015).To the best of our knowledge, there are no other published reports on chromatic aberrancies in C. hortulana.
Here, we report and describe two cases of yellow, patternless (xanthic) specimens of Corallus hortulana collected in the Department of Beni, Bolivia.The individuals were identified following Henderson (1993Henderson ( , 1997Henderson ( , 2002) ) and Peters and Orejas-Miranda (1970) based on the following diagnostic characters: strongly laterally compressed body with smooth dorsal scales (midbody dorsal scale count 37-63); scales of the head: subocular scales present and in contact with supralabial scales; loreal scale fragmented and numerous infraloreal scales present; and nasal scales in contact and separating internasals from rostral.
The first specimen was collected in Yacuma Province, 100 m west of the bank of the Mamoré River, by a trail to the community of Exaltación (13°18'10.69"S,65°14'45.96"W),on June 15, 2015, at 00:32 h, by R.L. Powell, C.B. Eversole, and D. Lizarro, during a herpetofaunal survey.The snake was found 2.5 m high in a tree in primary forest.The specimen is a female measuring 102 cm snout to vent length, 21.7 cm tail length, with a live weight of 180 g.(Figure 1).The specimen was deposited in the Colección de Historia Natural de Herpetología, Centro de Investigación de Recursos Acuáticos, Universidad Autónoma del Beni José Ballivián .
The second individual was also found during a herpetofaunal survey in Yacuma Province, by the east bank of the Niquisi River (13°56'22.36"S,65°13'4.06"W),adjacent to an oxbow lake of the Mamoré River, in the vicinity of the Toboso community (Canichana Community Land of Origin) on September 26, 2017, at 22:31 h; L.R. Rivas, and R. Chungara.The snake was found 2.3 m high in tree.The individual was not collected and its sex was not determined.It was examined, measured (total length = 150 cm), photographed [vouchered photo record: CIRA(VP)-851] (Figure 2) and released on the site of capture.
Both individuals in life were yellow and patternless with a white ventral region, and had a few flecks of light tan scales and numerous scattered small areas (2-5 scales) without pigmentation on the dorsum.The eye pigmentation of both specimens was yellow.The records were within 70 km of each other (Figure 3).
Yellow, patternless individuals of C. hortulana have been recognized as within the species polychromatic range (referred to as character states or morphotypes) (Henderson et al. 1995;Stafford and Henderson 1996;Henderson 1993Henderson , 1997Henderson , 2002;;Duarte et al. 2015).Among 112 preserved specimens from the Amazon basin examined by Duarte et al. (2015), only two were light-colored, patternless individuals.Henderson (1997Henderson ( , 2002) ) examined more than 600 specimens from throughout the species' range, including over 170 specimens from mainland South America; less than 5.9% were flecked or patternless yellow individuals, none of them from Bolivia.

ACTA AMAZONICA
While Henderson (1997) and Duarte et al. (2015) made important contributions via their detailed analyses of morphotypes and color patterns of C. hortulana, we argue that the light-colored, designless Morphotype 6 of Duarte et al. (2015), as well as the yellow, flecked Character State 6 and yellow, patternless Character State 7 of Henderson (1997) all meet the criteria of xanthism (i.e., overexpression of yellow pigmentation associated with the lack of red, brown, or black pigmentation) (Harris 1970;Bechtel 1978Bechtel , 1995;;Dyrkacz 1981;Borteiro et al. 2021).
Interestingly, Borteiro et al. (2021) reported that xanthism in neotropical snakes was rarely observed and was only documented in nocturnal species (which would include C. hortulana).Our records are the first report of xanthism in C. hortulana in Bolivia, and contribute to the understanding of the occurrence and distribution of chromatic aberrancies in wild populations of this species.

ACKNOWLEDGMENTS
The General Directorate of Biodiversity and Protected Areas for collection permits (Bolivia) and the Centro de Investigación de Recursos Acuáticos (CIRA), Universidad Autónoma del Beni "José Ballivian" for logistical support.We wish to thank the people of the Canichana Community Lands of Origin.Special thanks to Dr. Diego Baldo, Laboratorio

Figure 2 .
Figure 2. Adult Corallus hortulana (CIRA(VP)-851) recorded in Yacuma Province, Department of Beni, Bolivia.A -overall view; B -detail of the head.Credit: L.R. Rivas.This figure is in color in the electronic version.