Parallel lasers and digital photography to estimate limb size of chimpanzees (Pan troglodytes) at Ngogo, Kibale National Park, Uganda.

How animals grow and when they stop growing are key variables for understanding life history evolution. Although theoretically straightforward, it is logistically difficult to take body size measurements of wild animals, especially endangered and arboreal primates. Here we employ a method that has gained popularity over the past decade: digital photography combined with parallel lasers. Two laser pointers are set at a known distance apart and then projected on the animal to act as a scale in the photograph. We used this method to estimate limb length and width in a large, cross-sectional sample of mid- to late-adolescent and young adult male chimpanzees at Ngogo in Kibale National Park, Uganda. After several years of modifying our methods, we present a protocol for estimating limb length and width in wild chimpanzees. We found that by mid- to late-adolescence, male chimpanzees have reached adult height, as chimpanzees between 12 and 20 years of age did not differ in their forearm or lower leg lengths. However, mid- to late-adolescent male chimpanzees appear to continue gaining mass, as we found a weak but positive correlation between age and limb width for both forearms and lower legs. Although our method proved relatively precise, we encountered several sources of error throughout this study, such as ensuring that the lasers were indeed parallel and in identifying anatomical landmarks in the photographs. We discuss these challenges with the hope of increasing transparency and collaboration in future studies of primate body size.

Blood lead levels in Peruvian adults are associated with proximity to mining and DNA methylation.

BACKGROUND: Inorganic lead (Pb) is common in the environment, and is toxic to neurological, renal, and cardiovascular systems. Pb exposure influences the epigenome with documented effects on DNA methylation (DNAm). We assessed the impact of low levels of Pb exposure on DNAm among non-miner individuals from two locations in Peru: Lima, the capital, and Cerro de Pasco, a highland mining town, to study the effects of Pb exposure on physiological outcomes and DNAm. METHODS: Pb levels were measured in whole blood (n = 305). Blood leukocyte DNAm was determined for 90 DNA samples using the Illumina MethylationEPIC chip. An epigenome-wide association study was performed to assess the relationship between Pb and DNAm. RESULTS: Individuals from Cerro de Pasco had higher Pb than individuals from Lima (p-value = 2.00E-16). Males had higher Pb than females (p-value = 2.36E-04). Pb was positively associated with hemoglobin (p-value = 8.60E-04). In Cerro de Pasco, blood Pb decreased with the distance from the mine (p-value = 0.04), and association with soil Pb was approaching significance (p-value = 0.08). We identified differentially methylated positions (DMPs) associated with genes SOX18, ZMIZ1, and KDM1A linked to neurological function. We also found 45 differentially methylated regions (DMRs), seven of which were associated with genes involved in metal ion binding and nine to neurological function and development. CONCLUSIONS: Our results demonstrate that even low levels of Pb can have a significant impact on the body including changes to DNAm. We report associations between Pb and hemoglobin, Pb and distance from mining, and between blood and soil Pb. We also report associations between loci- and region-specific DNAm and Pb.