Mercury Bioaccumulation in Two Species of Insectivorous Bats from Urban China: Influence of Species, Age, and Land Use Type

Inter- and intraspecific variability of total mercury concentrations in bats of Texas (USA)

Exposure to mercury (Hg) may cause deleterious health effects in wildlife, including bats. Texas produces more Hg pollution than any other state in the United States, yet only one study has examined Hg accumulation in bats. This study measured the concentration of total Hg (THg) in fur (n = 411) collected from ten bat species across 32 sites in eastern and central Texas, USA. Fur THg concentrations were compared among species, and when samples sizes were large enough, between sex and life stage within a species, and the proximity to coal-fired power plants. For all sites combined and species with a sample size ≥8, mean THg concentrations (μg/g dry weight) were greatest in tri-colored bats (Perimyotis subflavus; 6.04), followed by evening bats (Nycticeius humeralis; 5.89), cave myotis (Myotis velifer; 2.11), northern yellow bats (Lasiurus intermedius; 1.85), Brazilian free-tailed bats (Tadarida brasiliensis; 1.03), and red bats (Lasiurus borealis/blossevillii; 0.974), and lowest in hoary bats (Lasiurus cinereus; 0.809). Within a species, fur THg concentrations did not significantly vary between sex for the five examined species (red bat, northern yellow bat, cave myotis, evening bat, Brazilian free-tailed bat) and only between life stage in evening bats. Site variations in fur THg concentrations were observed for evening bats, tri-colored bats, and Brazilian free-tailed bats. Evening bats sampled closer to point sources of Hg pollution had greater fur THg concentrations than individuals sampled further away. Sixteen percent of evening bats and 8.7% of tri-colored bats had a fur THg concentration exceeding the 10 μg/g toxicity threshold level, suggesting that THg exposure may pose a risk to the health of bats in Texas, particularly those residing in east Texas and on the upper Gulf coast. The results of this study can be incorporated into future management and recovery plans for bats in Texas.

A systematic review of trace elements in the tissues of bats (Chiroptera)

Bats constitute about 22% of known mammal species; they have various ecological roles and provide many ecosystem services. Bats suffer from several threats caused by anthropization, including exposure to toxic metals and metalloids. We analyzed 75 papers in a systematic literature review to investigate how species, diet, and tissue type impact bioaccumulation. Most studies documented element accumulation in fur, liver, and kidney; at least 36 metals and metalloids have been measured in bat tissues, among the most studied were mercury and zinc. Comparisons with known toxicological thresholds for other mammals showed concerning values for mercury and zinc in bat hair, lead and some essential metals in liver, and iron and calcium in kidneys. Moreover, accumulation patterns in tissues differed depending on bat diet: insectivorous bats showed higher metal concentrations in fur than in liver and kidney while frugivorous species showed higher values in liver and kidney than in fur. Finally, among the bat species that have been studied in more than two papers, the big brown bat (Eptesicus fuscus) show values of mercury in hair and copper in liver that exceed the known thresholds; as does copper in the liver of the little brown bat (Myotis lucifugus). Most studies have been conducted in temperate North America and Eurasia, areas with the lowest bat species diversity; there is a paucity of data on tropical bat species. This review points out several information gaps in the understanding of metal contamination in bats, including a lack of measured toxicity thresholds specific for bat tissues. Data on trace element bioaccumulation and its associated health effects on bats is important for conservation of bat species, many of which are threatened.

Mercury entomotoxicology

Mercury is an industrial pollutant of global concern. Currently entomofauna is disappearing and chemical pollution is one cause, however, it is unknown whether mercury is an additional threat. Therefore, it is necessary to know the entomotoxicology of mercury. The aim of the present work was to perform a comprehensive literature review on the entomotoxicology of mercury. The toxicokinetics and toxicity of mercury in insects, the participation of insects in the mercury cycle and the fact that this element is a threat to entomofauna are characterized. Insects can be exposed to mercury through ingestion, tracheal respiration, and gill respiration. Organic forms of mercury are better absorbed, bioaccumulated and distributed than inorganic forms. In addition, insects can biotransform mercury, for example, by methylating it. Metal elimination occurs through feces, eggs and exuvia. Toxicity molecular mechanisms include oxidative stress, enzymatic disruptions, alterations in the metabolism of neurotransmitters and proteins, genotoxicity, cell death and unbalances in the energetic state. Moreover, mercury affects lipid, germ, and gut cells, causes deformations, disturbs development, reproduction, behavior, and locomotion, besides to alters insect populations and communities. In terrestrial ecosystems, entomofauna participate in the mercury cycle by bioaccumulating mercury from soil and air, predating, being predated and decomposing organic matter. In aquatic ecosystems insects participate by accumulating mercury from water and sediment, predating, being predated and transporting it to terrestrial ecosystems when they emerge as winged adults. There are still information gaps that need to be addressed.

Land use, season, and parasitism predict metal concentrations in Australian flying fox fur

Urban-living wildlife can be exposed to metal contaminants dispersed into the environment through industrial, residential, and agricultural applications. Metal exposure carries lethal and sublethal consequences for animals; in particular, heavy metals (e.g. arsenic, lead, mercury) can damage organs and act as carcinogens. Many bat species reside and forage in human-modified habitats and could be exposed to contaminants in air, water, and food. We quantified metal concentrations in fur samples from three flying fox species (Pteropus fruit bats) captured at eight sites in eastern Australia. For subsets of bats, we assessed ectoparasite burden, haemoparasite infection, and viral infection, and performed white blood cell differential counts. We examined relationships among metal concentrations, environmental predictors (season, land use surrounding capture site), and individual predictors (species, sex, age, body condition, parasitism, neutrophil:lymphocyte ratio). As expected, bats captured at sites with greater human impact had higher metal loads. At one site with seasonal sampling, bats had higher metal concentrations in winter than in summer, possibly owing to changes in food availability and foraging. Relationships between ectoparasites and metal concentrations were mixed, suggesting multiple causal mechanisms. There was no association between overall metal load and neutrophil:lymphocyte ratio, but mercury concentrations were positively correlated with this ratio, which is associated with stress in other vertebrate taxa. Comparison of our findings to those of previous flying fox studies revealed potentially harmful levels of several metals; in particular, endangered spectacled flying foxes (P. conspicillatus) exhibited high concentrations of cadmium and lead. Because some bats harbor pathogens transmissible to humans and animals, future research should explore interactions between metal exposure, immunity, and infection to assess consequences for bat and human health.

Do We Need to Use Bats as Bioindicators?

Simple Summary

Bioindicators are organisms that react to the quality or characteristics of the environment and their changes. They are vitally important to track environmental alterations and take action to mitigate them. As choosing the right bioindicators has important policy implications, it is crucial to select them to tackle clear goals rather than selling specific organisms as bioindicators for other reasons, such as for improving their public profile and encourage species conservation. Bats are a species-rich mammal group that provide key services such as pest suppression, pollination of plants of economic importance or seed dispersal. Bats show clear reactions to environmental alterations and as such have been proposed as potentially useful bioindicators. Based on the relatively limited number of studies available, bats are likely excellent indicators in habitats such as rivers, forests, and urban sites. However, more testing across broad geographic areas is needed, and establishing research networks is fundamental to reach this goal. Some limitations to using bats as bioindicators exist, such as difficulties in separating cryptic species and identifying bats in flight from their calls. It is often also problematic to establish the environmental factors that influence the distribution and behaviour of bats.

Abstract

Bats show responses to anthropogenic stressors linked to changes in other ecosystem components such as insects, and as K-selected mammals, exhibit fast population declines. This speciose, widespread mammal group shows an impressive trophic diversity and provides key ecosystem services. For these and other reasons, bats might act as suitable bioindicators in many environmental contexts. However, few studies have explicitly tested this potential, and in some cases, stating that bats are useful bioindicators more closely resembles a slogan to support conservation than a well-grounded piece of scientific evidence. Here, we review the available information and highlight the limitations that arise in using bats as bioindicators. Based on the limited number of studies available, the use of bats as bioindicators is highly promising and warrants further investigation in specific contexts such as river quality, urbanisation, farming practices, forestry, bioaccumulation, and climate change. Whether bats may also serve as surrogate taxa remains a controversial yet highly interesting matter. Some limitations to using bats as bioindicators include taxonomical issues, sampling problems, difficulties in associating responses with specific stressors, and geographically biased or delayed responses. Overall, we urge the scientific community to test bat responses to specific stressors in selected ecosystem types and develop research networks to explore the geographic consistency of such responses. The high cost of sampling equipment (ultrasound detectors) is being greatly reduced by technological advances, and the legal obligation to monitor bat populations already existing in many countries such as those in the EU offers an important opportunity to accomplish two objectives (conservation and bioindication) with one action.

Wing membrane and Fur as indicators of metal exposure and contamination of internal tissues in bats

All European bats are protected by the EU and Associated Members legal regulations. Being insectivorous and top predators, they can be particularly exposed to persistent organic and inorganic pollutants. It is surprising how little is known about the impact of environmental pollutants on bats from physiological to populational levels. In this study we focused on contamination with trace metals of first-year bats from Kharkiv city, NE Ukraine. Tissues from the carcasses of two species, Nyctalus noctula (n = 20) and Eptesicus serotinus (n = 20), were used for metal analysis. The samples of external (wing membrane, fur) and internal (liver, lung, kidney, bones) tissues were analysed for contents of Pb, Cu, Zn, and Cd to see whether fur or wing membrane can be used as proxies for metal contamination of the vital internal tissues. In E. serotinus, significant positive correlations in Pb concentrations were found between all external and internal tissues. For Cd only, correlation between the fur and lung was found, for Cu between the fur and liver, and for Zn between the fur and kidney. In contrast, for N. noctula, only one such correlation was found - between Zn concentrations in the fur and kidney. The tissues differed significantly in concentrations of all studied metals, with no difference between the species. The results showed that the fur and wing membrane can be used as good proxies for Pb concentrations in internal organs of E. serotinus, but not necessarily for other metals or for N. noctula. The results for Pb are, however, encouraging enough to conclude that the topic is worth further studies, covering more species, a wider age range and more diverse environments.

Mercury bioaccumulation in tropical bats from a region of active artisanal and small-scale gold mining

Mercury negatively affects human and animal health. Artisanal and small-scale gold mining can be a major local source of mercury contamination, especially into aquatic systems in tropical areas. Animals associated with mercury-contaminated aquatic systems are at high risk of experiencing effects of this heavy metal, but it is not clear how far the effects may extend into nearby terrestrial systems. We report mercury contamination levels in bats in agricultural areas at increasing distances from gold mining (~3-89 km of distance). We hypothesized that bat mercury concentrations would differ between feeding guilds, land use types, and be higher at sites closer to gold mining areas. We collected 112 fur samples from 30 bat species and eight guilds, and provide the first reports of concentrations in 12 species. All mercury concentrations were below the level at which health is likely to be affected (10 ppm). We found guild-influenced differences among mercury concentration levels, with the highest concentrations in aerial insectivores and carnivores, and the lowest in canopy frugivores. Our results suggest insectivorous and carnivorous bats may still be at some risk even at sites distant from aquatic mercury contamination. We did not find an effect of agricultural land-use type on mercury concentrations within species or guilds, suggesting mercury contamination did not extend to agricultural sites from areas of gold mining activities, and that these agricultural activities themselves were not an important source of mercury. We conclude bats did not demonstrate a signature of mercury risk either as a result of proximity of gold mining, or as a result of agricultural activities.

Research trends on bats in China: A twenty-first century review

In this century, China has sustained unparalleled economic development, leading to exponentially growing investments in scientific research. Yet, the demand for research-funding is large and tracing the current knowledge is a key step to define priority research topics. In this same span, studies on bats in China have uncovered an overlooked diversity and revealed novelties in bats’ evolutionary history and life-history aspects. All this 21st-century knowledge, however, is scattered and a large part is concealed from most of the international scientific community in Mandarin-language articles. Here, we summarize the post-millennium (2000–2017) research on bats in China and point out trends and future directions based on neglected topics, groups, and regions. In addition, we provide an up-to-date list of bat species in China. We retrieved 594 publications related to bats in China, nearly half were written in Mandarin. At least 147 bat species are present in China, which places it among the most bat-rich countries in the world. There was a significant positive trend on the number of publications, from 12.5 annual average in 2000–2005 to 46.5 in recent years, reflecting the Chinese economic-scientific development in this century. We found marked taxonomic and spatial biases. Half of the studies in this century focused on Rhinolophus, Myotis, and Hipposideros, and the southern and eastern provinces were the most studied. Systematic/taxonomy and Ecology were the predominant topics post-millennium, whereas only 10 articles have clear conservation-driven goals. Our review shows that the majority of studies were focused on the least concern, cave-dweller species, and on bat-rich provinces. Future projects should address the effects of human-modified landscapes on bat community to define proper conservation actions. We discuss some priority actions and projects that will help to enhance bat protection in China.