Anomalous pigmentation in American primates: Review and first record of a Leucistic Black Howler Monkey in Southeast Mexico

Leucism is an aberration of color that occurs in individuals as a consequence of genetic mutations. Along with albinism and piebaldism, leucism is one of the most commonly reported types of chromatic anomalies in mammals, however, detailed descriptions of such conditions are rare. We report the first record of a leucistic black howler monkey (Alouatta pigra) in southern Mexico, an apparently healthy individual who was the male of a typical black howler group. Additionally, we compiled records of anomalous pigmentation in American primates published in peer-reviewed journals between 1960 and 2021, as well as social media posts regarding casual observations of individuals with such conditions. We found 11 scientific articles which described 13 records of anomalous pigmentation in a total of 44 individuals, from five species, three subspecies and one hybrid. Leucism was the most widely reported condition with six records. We discovered 19 online posts of 20 individuals with anomalous pigmentation, which included two species not reported in scientific literature. Our results suggest that anomalous coloration is not a significant threat to survival, but its occurrence raises interesting, and possibly alarming, questions about the causes of such conditions. We encourage researchers and civil society to formally report such observations of animals with color aberrations, to expand upon the understanding of this phenomenon and to get involved in the conservation of tropical forests.