Predictors and immunological correlates of sublethal mercury exposure in vampire bats

Mercury (Hg) is a pervasive heavy metal that often enters the environment from anthropogenic sources such as gold mining and agriculture. Chronic exposure to Hg can impair immune function, reducing the ability of animals to resist or recover from infections. How Hg influences immunity and susceptibility remains unknown for bats, which appear immunologically distinct from other mammals and are reservoir hosts of many pathogens of importance to human and animal health. We here quantify total Hg (THg) in hair collected from common vampire bats ( Desmodus rotundus ), which feed on blood and are the main reservoir hosts of rabies virus in Latin America. We examine how diet, sampling site and year, and bat demography influence THg and test the consequences of this variation for eight immune measures. In two populations from Belize, THg concentrations in bats were best explained by an interaction between long-term diet inferred from stable isotopes and year. Bats that foraged more consistently on domestic animals exhibited higher THg. However, relationships between diet and THg were evident only in 2015 but not in 2014, which could reflect recent environmental perturbations associated with agriculture. THg concentrations were low relative to values previously observed in other bat species but still correlated with bat immunity. Bats with higher THg had more neutrophils, weaker bacterial killing ability and impaired innate immunity. These patterns suggest that temporal variation in Hg exposure may impair bat innate immunity and increase susceptibility to pathogens such as bacteria. Unexpected associations between low-level Hg exposure and immune function underscore the need to better understand the environmental sources of Hg exposure in bats and the consequences for bat immunity and susceptibility.

Diet of the western pygmy possum, Cercartetus concinnus Gould (Marsupialia: Burramyidae), at Innes National Park, South Australia, and evaluation of diet sampling methods

The diet of a population of western pygmy possums, Cercartetus concinnus Gould (Marsupialia: Burramyidae), at Innes National Park, South Australia, was examined using faecal and fur pollen swab samples in relation to monthly plant phenological data. Eucalyptus pollen was the most abundant in both faeces and in fur swab samples, followed by Melaleuca pollen; plant exudates could not be examined by this study. Moth scales were found in 26% of the scat samples. Faecal samples comprised most plant species identified (15 of 17), but up to 25% of plant species recorded from fur pollen swabs were not recorded from faeces. The relatively high frequencies of plant species represented in fur pollen swabs indicates that this method is valuable for supplementing faecal analysis used to determine plant visitation by nectarivorous animals.

Daily dietary intake of chromium in southern Spain measured with duplicate diet sampling

We measured daily dietary Cr intake in southern Spain by sampling duplicate diets for seven consecutive days in different population groups. Cr was determined by electrothermal atomization–atomic absorption spectrometry. The samples were mineralized in a digestion block with HNO3, HClO4and V2O5. A total of 161 duplicate diets from twenty-three subjects were analysed, and mean levels of Cr intake ranged from 9·39 to 205·16 μg/d. Mean Cr intake (100 μg/d) was similar to levels found for most other countries, and was within the range recommended by the National Research Council for a safe and adequate daily intake (50–200 μg/d). Chromium intake correlated significantly with energy, protein and carbohydrate intake, and with the daily intake of Zn, Fe, Mg, K, Na, Ca and nicotinic acid in the diets analysed.