Signs of adaptation to trace metal contamination in a common urban bird

Blood lead increases and haemoglobin decreases in urban birds along a soil contamination gradient in a mining city

Lead contaminated soil is a persistent global threat to the health of animal populations. Nevertheless, links between soil lead and its adverse effects on exposed wildlife remain poorly understood. Here, we explore local geographic patterns of exposure in urban birds along a gradient of lead contamination in Broken Hill, an Australian mining city. Soil lead concentrations are linked to co-located blood lead measurements in rock pigeons (Columba livia), house sparrows (Passer domesticus), crested pigeons (Ocyphaps lophotes) and white-plumed honeyeaters (Lichenostomus ornatus). Median blood lead levels were highest in crested pigeons (59.6 μg/dL), followed by house sparrows (35.2 μg/dL), rock pigeons (35.1 μg/dL), and white-plumed honeyeaters (27.4 μg/dL). Blood lead levels in all species declined away from mining areas, the primary source of lead contamination in Broken Hill. Blood lead increased significantly and at the greatest rate relative to soil lead in the three ground foraging species (crested pigeons, house sparrows, rock pigeons). For these species, soil lead concentrations below 200 mg/kg and 900 mg/kg were needed to maintain a median blood lead concentration under the lower threshold of the subtoxic (20-50 μg/dL) and toxic (≥ 50 μg/dL) effect ranges previously identified for some bird species. We also investigated the effects of lead exposure on blood haemoglobin levels as a general measure of physiological condition in birds exposed to different levels of soil lead contamination. Overall, for every 1 μg/dL increase in blood lead, haemoglobin decreased by 0.11 g/L. The rate of this decrease was not significantly different between species, which supports the measurement of haemoglobin as a robust though insensitive measure of physiological condition in chronically lead exposed birds. Our findings reflect the importance of lead contaminated soil as a widespread source of elevated blood lead and supressed haemoglobin levels in birds inhabiting urbanised and mining impacted environments.

Exposure to Sublethal Concentrations of Lead (Pb) Affects Ecologically Relevant Behaviors in House Sparrows (Passer domesticus)

Global contamination of environments with lead (Pb) poses threats to many ecosystems and populations. While exposure to Pb is toxic at high concentrations, recent literature has shown that lower concentrations can also cause sublethal, deleterious effects. However, there remains relatively little causal investigation of how exposure to lower concentrations of environmental Pb affects ecologically important behaviors. Behaviors often represent first-line responses of an organism and its internal physiological, molecular, and genetic responses to a changing environment. Hence, better understanding how behaviors are influenced by pollutants such as Pb generates crucial information on how species are coping with the effects of pollution more broadly. To better understand the effects of sublethal Pb on behavior, we chronically exposed adult wild-caught, captive house sparrows (Passer domesticus) to Pb-exposed drinking water and quantified a suite of behavioral outcomes: takeoff flight performance, activity in a novel environment, and in-hand struggling and breathing rate while being handled by an experimenter. Compared to controls (un-exposed drinking water), sparrows exposed to environmentally relevant concentrations of Pb exhibited decreases in takeoff flight performance and reduced movements in a novel environment following 9-10 weeks of exposure. We interpret this suite of results to be consistent with Pb influencing fundamental neuro-muscular abilities, making it more difficult for exposed birds to mount faster movements and activities. It is likely that suppression of takeoff flight and reduced movements would increase the predation risk of similar birds in the wild; hence, we also conclude that the effects we observed could influence fitness outcomes for individuals and populations altering ecological interactions within more naturalistic settings.

Past and future: Urbanization and the avian endocrine system

Urban environments are evolutionarily novel and differ from natural environments in many respects including food and/or water availability, predation, noise, light, air quality, pathogens, biodiversity, and temperature. The success of organisms in urban environments requires physiological plasticity and adjustments that have been described extensively, including in birds residing in geographically and climatically diverse regions. These studies have revealed a few relatively consistent differences between urban and non-urban conspecifics. For example, seasonally breeding urban birds often develop their reproductive system earlier than non-urban birds, perhaps in response to more abundant trophic resources. In most instances, however, analyses of existing data indicate no general pattern distinguishing urban and non-urban birds. It is, for instance, often hypothesized that urban environments are stressful, yet the activity of the hypothalamus-pituitary-adrenal axis does not differ consistently between urban and non-urban birds. A similar conclusion is reached by comparing blood indices of metabolism. The origin of these disparities remains poorly understood, partly because many studies are correlative rather than aiming at establishing causality, which effectively limits our ability to formulate specific hypotheses regarding the impacts of urbanization on wildlife. We suggest that future research will benefit from prioritizing mechanistic approaches to identify environmental factors that shape the phenotypic responses of organisms to urbanization and the neuroendocrine and metabolic bases of these responses. Further, it will be critical to elucidate whether factors affect these responses (a) cumulatively or synergistically; and (b) differentially as a function of age, sex, reproductive status, season, and mobility within the urban environment. Research to date has used various taxa that differ greatly not only phylogenetically, but also with regard to ecological requirements, social systems, propensity to consume anthropogenic food, and behavioral responses to human presence. Researchers may instead benefit from standardizing approaches to examine a small number of representative models with wide geographic distribution and that occupy diverse urban ecosystems.

Increased lead and glucocorticoid concentrations reduce reproductive success in house sparrows along an urban gradient

Urbanization is increasing at a rapid pace globally. Understanding the links among environmental characteristics, phenotypes, and fitness enables researchers to predict the impact of changing landscapes on individuals and populations. Although avian reproductive output is typically lower in urban compared with natural areas, the underlying reasons for this discrepancy may lie at the intersection of abiotic and biotic environmental and individual differences. Recent advances in urban ecology highlight the effect of heavy metal contamination on stress physiology. As high levels of glucocorticoid hormones decrease parental investment, these hormones might be the link to decreased reproductive success in areas of high environmental pollution. In this study, we aimed to identify which abiotic stressors are linked to avian reproductive output in urban areas and whether this link is mediated by individual hormone levels. We used fine-scaled estimates (2 m2 spatial resolution) of nighttime light, noise, and urban density to assess their impacts on the physiological condition of adult house sparrows (Passer domesticus). We measured circulating levels of lead and glucocorticoid concentrations in 40 breeding pairs of free-living house sparrows and related these physiological traits to reproductive success. Using structural equation modeling, we found that increased urban density levels linked directly to increased plasma corticosterone and lead concentrations that subsequently led to decreased fledgling mass. Sparrows with increased lead concentrations in plasma also had higher corticosterone levels. Although urban areas may be attractive due to decreased natural predators and available nesting sites, they may act as ecological traps that increase physiological damage and decrease fitness. To illustrate, avian development is strongly explained by parental corticosterone levels, which vary significantly in response to urban density and lead pollution. With fine-scale ecological mapping for a species with small home ranges, we demonstrated the presence and impacts of urban stressors in a small city with high human densities.

A Theory of City Biogeography and the Origin of Urban Species

Many of the choices humans make with regard to infrastructure, urban planning and other phenomena have impacts that will last thousands of years. This can readily be seen in modern cities in which contemporary streets run along street grids that were laid out thousands of years prior or even in which ancient viaducts still play a role. However, rarely do evolutionary biologists explicitly consider the future of life likely to be associated with the decisions we are making today. Here, we consider the evolutionary future of species in cities with a focus on the origin of lineages and species. We do so by adjusting evolutionary predictions from the theory of island biogeography so as to correspond to the unique features of cities as islands. Specifically, the species endemic to cities tend to be associated with the gray habitats in cities. Those habitats tend to be dominated by human bodies, pet bodies and stored food. It is among such species where the origin of new lineages is most likely, although most research on evolution in cities has focused on green habitats. We conclude by considering a range of scenarios for the far future and their implications for the origin of lineages and species.

Spring colonies of the ant Temnothorax nylanderi tolerate cadmium better than winter colonies, in both a city and a forest habitat

A recent study showed that, in the ant Temnothorax nylanderi, city colonies are more tolerant to cadmium than forest colonies. However, because of annual variation in biological factors (e.g. body size, anti-stress protein production or trace metal accumulation rate), trace metal tolerance may vary over the year. We aimed at testing whether tolerance to cadmium of colonies of T. nylanderi differs between two different seasons within the same year (winter and spring). We also assessed whether the better cadmium tolerance of city colonies was constant over these two different time points. We collected colonies at the end of their hibernation period (winter colonies) and several weeks after (spring colonies) from two different habitats (forest and city) to assess whether response to cadmium was consistent regardless of the environment. We exposed colonies to a cadmium or a control treatment for 61 days. We compared tolerance to cadmium between spring/winter and city/forest colonies by measuring several life history traits. We found that spring colonies tolerates cadmium better than winter colonies, and that city colonies have a higher tolerance to cadmium but only in spring. Although further studies with replicated pairs of city/forest habitats and different years will be necessary to confirm those results, our study suggests that tolerance to trace metals can fluctuate along the yearly cycle.

Evolution in Cities

Although research performed in cities will not uncover new evolutionary mechanisms, it could provide unprecedented opportunities to examine the interplay of evolutionary forces in new ways and new avenues to address classic questions. However, while the variation within and among cities affords many opportunities to advance evolutionary biology research, careful alignment between how cities are used and the research questions being asked is necessary to maximize the insights that can be gained. In this review, we develop a framework to help guide alignment between urban evolution research approaches and questions. Using this framework, we highlight what has been accomplished to date in the field of urban evolution and identify several up-and-coming research directions for further expansion. We conclude that urban environments can be used as evolutionary test beds to tackle both new and long-standing questions in evolutionary biology.

Hibernation Conditions Contribute to the Differential Resistance to Cadmium between Urban and Forest Ant Colonies

Simple Summary

The resistance of organisms to trace metals can have a genetic or a plastic origin. Indeed, differential environmental conditions experienced before the exposure to trace metals could physiologically condition organisms and plastically enhance their subsequent resistance to trace metals. In this study on the ant Temnothorax nylanderi, we investigated whether the better cadmium resistance of urban colonies relative to forest colonies could originate from the distinct hibernation conditions that they experienced prior to cadmium exposure. We compared the ability of urban and forest colonies to resist cadmium depending on whether they had hibernated in their respective urban or forest habitats or under a laboratory common garden setup. We found that urban colonies resisted cadmium better than forest colonies when they had hibernated under a common garden. Surprisingly, this difference was not observed between urban and forest colonies that had hibernated in the field, in contrast with a previous study. One reason may be that winter was particularly mild on the year of our experiment. Our results therefore support the idea that urban colonies are genetically adapted to resist trace metals, but that this adaptation is only revealed under specific environmental conditions.

Abstract

Trace metals such as cadmium are found in high concentrations in urban environments. Animal and plant populations living in heavily contaminated environments could adapt to trace metals exposure. A recent study shows that urban populations of the acorn ant Temnothorax nylanderi are more resistant to cadmium than their forest counterparts. However, this study was performed using field colonies that had just come out of hibernation. Because urban and forest hibernation environments differ, the differential resistance to trace metals may originate either from differential hibernation conditions or from a different resistance baseline to cadmium. In this study, we tested these two hypotheses using laboratory common garden hibernation conditions. We let urban and forest colonies of the ant T. nylanderi hibernate under the same laboratory conditions for four months. After this hibernation period, we also collected field-hibernating colonies and we compared cadmium resistance between urban and forest colonies depending on the hibernation condition. We found a differential response to cadmium under common garden, with urban colonies displaying less larval mortality and lower size reduction of the produced individuals. This suggests a different resistance baseline of urban colonies to cadmium. However, unexpectedly, we did not detect the differential response between urban and forest colonies in the field, suggesting a more complex scenario involving both genetic and environmental influences.

The urban lead (Pb) burden in humans, animals and the natural environment

Centuries of human activities, particularly housing and transportation practices from the late 19th century through the 1980's, dispersed hundreds of millions of tons of lead into our urban areas. The urban lead burden is evident among humans, wild and domesticated animals, and plants. Animal lead exposures closely mirror and often exceed the lead exposure patterns of their human partners. Some examples: Pigeons in New York City neighborhoods mimicked the lead exposures of neighborhood children, with more contaminated areas associated with higher exposures in both species. Also, immediately following the lead in drinking water crisis in Flint MI in 2015, blood lead levels in pet dogs in Flint were 4 times higher than in surrounding towns. And combining lead's neurotoxicity with urban stress results in well-characterized aggressive behaviors across multiple species. Lead pollution is not distributed evenly across urban areas. Although average US pediatric lead exposures have declined by 90% since the 1970s, there remain well defined neighborhoods where children continue to have toxic lead exposures; animals are poisoned there, too. Those neighborhoods tend to have disproportionate commercial and industrial lead activity; a history of dense traffic; older and deteriorating housing; past and operating landfills, dumps and hazardous waste sites; and often lead contaminated drinking water. The population there tends to be low income and minority. Urban wild and domesticated animals bear that same lead burden. Soil, buildings, dust and even trees constitute huge lead repositories throughout urban areas. Until and unless we begin to address the lead repositories in our cities, the urban lead burden will continue to impose enormous costs distributed disproportionately across the domains of the natural environment. Evidence-based research has shown the efficacy and cost-effectiveness of some US public policies to prevent or reduce these exposures. We end with a series of recommendations to manage lead-safe urban environments.

Metalliferous Mining Pollution and Its Impact on Terrestrial and Semi-terrestrial Vertebrates: A Review

Metalliferous mining, a major source of metals and metalloids, has severe potential environmental impacts. However, the number of papers published in international peer-reviewed journals seems to be low regarding its effects in terrestrial wildlife. To the best of our knowledge, our review is the first on this topic. We used 186 studies published in scientific journals concerning metalliferous mining or mining spill pollution and their effects on terrestrial and semi-terrestrial vertebrates. We identified the working status of the mine complexes studied, the different biomarkers of exposure and effect used, and the studied taxa. Most studies (128) were developed in former mine sites and 46 in active mining areas. Additionally, although several mining accidents have occurred throughout the world, all papers about effects on terrestrial vertebrates from mining spillages were from Aznalcóllar (Spain). We also observed a lack of studies in some countries with a prominent mining industry. Despite >50% of the studies used some biomarker of effect, 42% of them only assessed exposure by measuring metal content in internal tissues or by non-invasive sampling, without considering the effect in their populations. Most studied species were birds and small mammals, with a negligible representation of reptiles and amphibians. The information gathered in this review could be helpful for future studies and protocols on the topic and it facilitates a database with valuable information on risk assessment of metalliferous mining pollution.

Sources of individual variation in problem-solving performance in urban great tits (Parus major): Exploring effects of metal pollution, urban disturbance and personality

Despite growing research effort, we have a limited understanding of how urban disturbance factors affect cognitive traits, such as innovative problem-solving. We performed an initial assessment of how metal pollution and urbanization levels on territories are related to problem-solving performance in urban great tits (Parus major), by presenting an obstacle removal test at nest boxes in three urban nest box populations that are exposed to different levels of metal pollution. We predicted that problem-solving capacity might be reduced within the most polluted population due to pollution-related neurological impairments. On the other hand, we predicted that problem-solving might positively correlate with urban disturbance levels on territories, because some past research suggests that problem-solving promotes persistence in urbanized habitats. We also assessed relationships between exploratory personality type, behavioral patterns during tests, and problem-solving performance, and examined the repeatability and fitness correlates of problem-solving. We found no evidence that behavioral patterns or problem-solving performance were related to metal exposure or exploratory personality, or that problem-solving promotes reproductive success. However, birds on territories exposed to more urban disturbance, as quantified by proximity to paths and roads, were more likely to problem-solve. Moreover, an aggressive problem-solving approach negatively predicted problem-solving success, and behavioral patterns during tests and problem-solving success were repeatable. Thus, rather than indicating negative effects of pollution or urban disturbance on problem-solving performance, our study provides preliminary support for the hypothesis that urbanization favors innovative problem-solving, and suggests that problem-solving could be associated with a personality dimension independent of exploratory personality.

Soft-Templating of Sulfur and Iron Dual-Doped Mesoporous Carbons: Lead Adsorption in Mixtures

Lead pollution in drinking water is one of the most common problems worldwide. In this research, sulfur and iron dual-doped mesoporous carbons are synthesized by soft-templating with sulfur content 4.4-6.1 atom% and iron content 7.8-9 atom%. Sulfur functionalities of the carbons are expected to enhance the affinity of the carbon toward lead whereas iron content is expected to separate the carbon from water owing to its magnetic properties. All the carbons were characterized by pore textural properties, x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX). In order to study the Pb(II) removal efficiently of this carbon in competitive mode and to mimic the real-world use, one additional heavy-metal, including Cr(III), and four other commonly occurring metals-Na(I), K(I), Ca(II) and Fe (III)-are added with lead prior to adsorption experiments. It was observed that Pb(II) adsorption capacity of this carbon was not influenced by the presence of other metals. A highly elevated concentration of Na(I), K(I), Ca(II) and Fe(III) in the eluting solution compared to the initial dose suggested possible leaching of those metals from other salts as impurities, water source or even from the carbon itself, although the XPS analysis of the carbon confirmed negligible adsorption of those metals in carbon. From the equilibrium and kinetic data of adsorption, few parameters have been calculated, including distribution coefficient, diffusive time constant and pseudosecond order rate constant. The overall results suggest that these iron and sulfur dual-doped mesoporous carbons can serve as potential adsorbents for removal of lead from drinking water in the presence of other competing metals.

Proximity to roads, but not exposure to metal pollution, is associated with accelerated developmental telomere shortening in nestling great tits

Comprehensively understanding the factors affecting physiology and fitness in urban wildlife requires concurrently considering multiple stressors. To this end, we simultaneously assessed how metal pollution and proximity to roads affect body condition and telomere shortening between days 8 and 15 of age in nestling great tits (Parus major), a common urban bird. We employed a repeated-measures sampling design to compare telomere shortening and body condition between nestlings from four urban study sites south of Antwerp, Belgium, which are located at different distances from a metal pollution point source. In addition, we explored associations between metal exposure and telomere dynamics on the individual level by measuring blood concentrations of five metals/metalloids, of which lead, copper and zinc were present at concentrations above the limit of detection. To assess whether roadway-associated stressors (e.g. noise and air pollution) might affect nestling condition and telomere shortening, we measured the proximity of nest boxes to roads. Metal exposure was not associated with nestling telomere length or body condition, despite elevated blood lead concentrations close to the metal pollution source (mean ± SE = 0.270 ± 0.095 μg/g wet weight at the most polluted study site), suggesting that nestlings may have some capacity to detoxify metals. However, nestlings from nest boxes near roads exhibited more telomere shortening between days 8 and 15 of age, and shorter telomeres at day 15. Nestlings in poorer condition also had shorter telomeres, but proximity to the road was unrelated to body condition. Thus, nutritional stress is unlikely to mediate the relationship between proximity to roads and telomere length. Rather, proximity to roads could have affected telomere shortening by exposing nestlings to air or noise pollution. Our study highlights that traffic-related pollution, which is implicated in human health problems, might also affect urban wildlife.

Response of a Small Mammal Population Postremediation for an In Situ Oil Pipeline Blowout on the Athabasca Oil Sands

Two releases from steam assisted gravity drainage (SAGD) wellheads occurred 3 yr apart. To track recovery of the affected areas, red-backed voles were studied 1 and 4 yr later, using population estimates, hepatic detoxification effort, body condition, and tissue metal levels as bioindicators of site recovery. From years 1 to 4, higher ethoxyresorufin-O-deethylase induction was no longer evident, capture rate was lower, and body lead residues were no longer (inversely) correlated with body condition. Environ Toxicol Chem 2019;38:1542-1548. © 2019 SETAC.

Mining and Planetary Health: A GeoHealth-Led Special Collection

Mining is a vital part of the global economy, but unmanaged releases of mine wastes can affect the health of humans, ecosystems, water, soil and Earth surface environments (e.g., rivers and estuaries). New technological developments and multidisciplinary collaborations are leading to new insights into the relationship between mining and the health of the Earth. In recognition of the importance of this topic, GeoHealth is leading in the creation of a special collection of papers on the theme of Mining and Planetary Health, to summarize the current state of knowledge, outline topics for urgent action and further research, and highlight positive efforts in environmental and health protection. Submissions are invited from researchers investigating the impacts of mining at the intersection of the Earth and environmental sciences and human, ecosystem, and planetary health.