Lead exposure and its relationship with fecal cortisol levels in black howler monkeys (Alouatta pigra)

Efficiently detecting early environmental threats to wildlife is vital for conservation. Beyond obvious dangers like habitat loss or deforestation, our study focuses on one of the most hazardous toxic metals for wildlife: lead (Pb). Pb is a widespread, cumulative, and insidious environmental pollutant that can trigger a wide range of physiological, biochemical, and behavioral disorders. In fact, Pb can cause permanent dysfunction of the major stress system, the hypothalamic pituitary adrenal (HPA) axis. We analyzed Pb and cortisol concentrations in fecal samples from Alouatta pigra in southern Mexico. Fecal samples were collected across six sites categorized as free-ranging (n = 65; conserved and disturbed) and from captive animals (n = 58). Additionally, we collected soil samples (n = 35). We found that Pb was present in 28% of fecal samples and 83% of soil samples. There was a positive relation between fecal and soil Pb levels, and fecal Pb concentration was negatively associated with cortisol levels. However, the claim of Pb being a direct interference with HPA axis requires further investigation. Given our findings, assessing wildlife exposure can be a valuable tool for understanding potential Pb exposure levels in the environment and its possible implications for human health. It can also serve as an early warning system of these consequences.

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.