Consequences of trace metal cocktail exposure in zebra finch (Taeniopygia guttata) and effect of calcium supplementation

Long-term changes in chemical components in the meadow pipit (Anthus pratensis) in the formerly heavily polluted Eastern Sudetes Mountains

The Eastern Sudetes Mountains (Northern Moravia, Czech Republic) were among the most polluted regions of Europe due to toxic metal depositions and acid rain, until the desulfurization of emissions from coal power stations and reduction of heavy industry which took place in the 1990s. This study provides a comparison of data on the levels of calcium, lead, cadmium, and aluminum in soil, meadow pipit (Anthus pratensis) nestlings, and their available diet in 1994-1999 and in 2017-2019. The soil pH and exchangeable amount of calcium and lead increased slightly. The concentration of calcium in potential prey (invertebrates) increased slightly, and lead and cadmium levels decreased. The amount of calcium and lead in nestling bodies decreased in 2017-2019, while cadmium and aluminum levels remained unchanged after accounting for nestling age. The age of nestlings had an effect on aluminum only, when its content decreased with age. The principal component analysis revealed close association between calcium and lead. The consequences of recent leaching of basic cations, mainly calcium, and increasing bioavailability of lead in soils for future reproduction of the meadow pipit are discussed.

Effects of persistent organic pollutants on telomere dynamics are sex and age-specific in a wild long-lived bird

Chemical pollution is a major man-made environmental threat to ecosystems and natural animal populations. Of concern are persistent organic pollutants (POPs), which can persist in the environment for many years. While bioaccumulating throughout the lives of wild animals, POPs can affect their health, reproduction, and survival. However, measuring long-term effects of POPs in wild populations is challenging, and therefore appropriate biomarkers are required in wildlife ecotoxicology. One potential target is telomere length, since telomere preservation has been associated to survival and longevity, and stressors as chemical pollution can disrupt its maintenance. Here, we investigated the effects of different classes of POPs on relative telomere length (RTL) and its rate of change (TROC) in wild long-lived Alpine swifts (Tachymarptis melba). As both RTL and TROC are often reported to differ between sexes and with chronological age, we tested for sex- and age-specific (pre-senescent vs. senescent, ≥ 9 age of years, individuals) effects of POPs. Our results showed that senescent females presented longer RTL and elongated telomeres over time compared to pre-senescent females and males. These sex- and age-related differences in RTL and TROC were influenced by POPs, but differently depending on whether they were organochlorine pesticides (OCPs) or industrial polychlorinated biphenyls (PCBs). OCPs (particularly drins) were negatively associated with RTL, with the strongest negative effects being found in senescent females. Conversely, PCBs led to slower rates of telomere shortening, especially in females. Our study indicates diametrically opposed effects of OCPs on RTL and PCBs on TROC, and these effects were more pronounced in females and senescent individuals. The mechanisms behind these effects (e.g., increased oxidative stress by OCPs; upregulation of telomerase activity by PCBs) remain unknown. Our results highlight the importance in wildlife ecotoxicology to account for sex- and age-related effects when investigating the health effects of pollutants on biomarkers such as telomeres.

The "parasite detoxification hypothesis": lead exposure potentially changes the ecological interaction from parasitism to mutualism

In urban areas, organisms are exposed to high pollutant levels, especially element trace metals that may impact host-parasite interactions. Indeed, parasites have been reported to reduce the negative effects of pollutants on their hosts. The fitness of parasitized organisms in polluted environments may therefore be greater than that of unparasitized organisms. In our study, we used an experimental approach to test this hypothesis on feral pigeons (Columba livia), which are endemically parasitized by nematodes and exposed to high levels of lead in urban areas. We tested the combined effects of lead exposure and helminth parasitism on different pigeon fitness components: preening, immunocompetence, abundance of lice (Columbicola columbae) and haemosporidian parasites (Heamoproteus spp., Plasmodium spp.), reproduction investment, and oxidative stress. Our results show that among pigeons exposed to lead treatment, individuals harboring nematode parasites exhibit more preening activity and have fewer ectoparasites lice than nematode-free individuals. Benefits for nematode-parasitized individuals exposed to lead were not detected for other fitness parameters. Further studies are required to confirm the "parasite detoxification hypothesis" in pigeons and to identify the mechanisms by which this detoxification occurs.

Inter-annual variation of physiological traits between urban and forest great tits

Urbanization is characterized by rapid environmental changes such as an increase in building surface, in pollution, or a decrease in invertebrate abundance. For many bird species, morphological and physiological differences have been observed between urban and rural individuals that seem to reflect a negative impact of urban life on the health and fitness of individuals. Studies on passerine birds also showed important differences between populations and species in their responses to the urban environment. We propose to test physiological differences between urban and forest individuals over 3 years to understand whether the observed patterns are constant or subject to variations across years. For this purpose, we assessed the health parameters of adults and fledgling of great tits, Parus major, living in an urban and in a forest site in the Eurometropole of Strasbourg, for three years. Bird health was estimated with morphological parameters (body condition and size) and also with physiological parameters (oxidative status and telomere length). Our results showed lower body condition of urban fledglings regardless of the year, but no site effects on telomere length. On the contrary, for adult breeders, urban individuals had longer telomeres than forest ones except for one year which coincide with bad weather conditions during reproduction where no difference was detected. Urban birds also had higher antioxidant capacity whatever the years. These results suggest that cities act as a filter in which only good quality individuals survive and achieve successful reproduction regardless of year, whereas in the forest the selection occurs only during harsh weather years.

Does oxidative stress shorten telomeres in vivo? A meta-analysis

Telomere attrition is considered a hallmark of ageing. Untangling the proximate causes of telomere attrition may therefore reveal important aspects about the ageing process. In a landmark paper in 2002 Thomas von Zglinicki demonstrated that oxidative stress accelerates telomere attrition in cell culture. In the next 20 years, oxidative stress became firmly embedded into modern theories of ageing and telomere attrition. However, a recent surge of in vivo studies reveals an inconsistent pattern questioning the unequivocal role of oxidative stress in telomere length and telomere attrition (henceforth referred to as telomere dynamics), in living organisms. Here we report the results of the first formal meta-analysis on the association between oxidative stress and telomere dynamics in vivo, representing 37 studies, 4969 individuals, and 18,677 correlational measurements. The overall correlation between oxidative stress markers and telomere dynamics was indistinguishable from zero (r = 0.027). This result was independent of the type of oxidative stress marker, telomere dynamic, or taxonomic group. However, telomere measurement method affected the analysis and the subset of TRF-based studies showed a significant overall correlation (r = 0.09), supporting the prediction that oxidative stress accelerates telomere attrition. The correlation was more pronounced in short-lived species and during the adult life phase, when ageing becomes apparent. We then performed an additional meta-analysis of interventional studies (n = 7) manipulating oxidative stress. This revealed a significant effect of treatment on telomere dynamics (d=0.36). Our findings provide new support for the hypothesis that oxidative stress causes telomere attrition in living organisms.

Telomeres and anthropogenic disturbances in wildlife: A systematic review and meta-analysis

Human-driven environmental changes are affecting wildlife across the globe. These challenges do not influence species or populations to the same extent and therefore a comprehensive evaluation of organismal health is needed to determine their ultimate impact. Evidence suggests that telomeres (the terminal chromosomal regions) are sensitive to environmental conditions and have been posited as a surrogate for animal health and fitness. Evaluation of their use in an applied ecological context is still scarce. Here, using information from molecular and occupational biomedical studies, we aim to provide ecologists and evolutionary biologists with an accessible synthesis of the links between human disturbances and telomere length. In addition, we perform a systematic review and meta-analysis on studies measuring telomere length in wild/wild-derived animals facing anthropogenic disturbances. Despite the relatively small number of studies to date, our meta-analysis revealed a significant small negative association between disturbances and telomere length (-0.092 [-0.153, -0.031]; n = 28; k = 159). Yet, our systematic review suggests that the use of telomeres as a biomarker to understand the anthropogenic impact on wildlife is limited. We propose some research avenues that will help to broadly evaluate their suitability: (i) further causal studies on the link between human disturbances and telomeres; (ii) investigating the organismal implications, in terms of fitness and performance, of a given telomere length in anthropogenically disturbed scenarios; and (iii) better understanding of the underlying mechanisms of telomere dynamics. Future studies in these facets will help to ultimately determine their role as markers of health and fitness in wildlife facing anthropogenic disturbances.

Honey bees cannot sense harmful concentrations of metal pollutants in food

Whether animals can actively avoid food contaminated with harmful compounds through taste is key to assess their ecotoxicological risks. Here, we investigated the ability of honey bees to perceive and avoid food resources contaminated with common metal pollutants known to impair behaviour at low concentrations. In laboratory assays, bees did not discriminate food contaminated with arsenic, lead or zinc and ingested it readily, up to estimated doses of 929.1 μg g^-1 As, 6.45 mg g^-1 Pb and 72.46 mg g^-1 Zn. A decrease of intake and appetitive responses indicating metal detection was only observed at the highest concentrations of lead (3.6 mM) and zinc (122.3 mM) through contact with the antennae and the proboscis. Electrophysiological analyses confirmed that only high concentrations of the three metals in a sucrose solution induced a consistently reduced neural response to sucrose in antennal taste receptors (As: >0.1 μM, Pb: >1 mM; Zn: >100 mM). Overall, cellular and behavioural responses did not provide evidence for specific mechanisms that would support selective detection of toxic metals (arsenic, lead), as compared to zinc, which has important biological functions. Our results thus show that honey bees can avoid metal pollutants in their food only at high concentrations unlikely to be encountered in the environment. By contrast, they appear to be unable to detect low, yet harmful, concentrations found in flowers. Metal pollution at trace levels is therefore a major threat for pollinators.

Avian blood and feathers as biological tools to track impacts from trace-metals: Bioaccumulation data from the biggest environmental disaster in Brazilian history

The Mariana's dam collapse was the worst environmental disaster in Brazilian history and one of the biggest worldwide. This perverse disaster resulted in the release of a contaminated mud tsunami that greatly impacted both aquatic and terrestrial biota. The aim of this study was to track environmental impacts resulting from Mariana's disaster using trace-element accumulation in avian blood and feathers as monitoring tool. For this, animals were collected at Doce River mouth (Regência), origin of the contaminated mud, and at southern (Aracruz) and northern (São Mateus) coastal areas. There were two sampling events (2018-2019), one during the winter period (first collection) and another during the summer period (second collection). Trace-element assessed were As, Cd, Cr, Cu, Fe, Pb, Hg, Mn and Zn. Findings show that inorganic contamination in birds followed a strong spatial and temporal behavior. In terms of time patterns, blood and feather contamination levels were markedly elevated in samples from the first collection event in comparison to the second. In terms of space, bioaccumulation was greater in Doce River mouth (Regência) and southern area (Aracruz). Additionally, levels found for Pb, Hg, As and Cd in birds from the first expedition were above proposed threshold levels, indicating possible health impacts. Finally, it is concluded that avian from areas impacted by Mariana's disaster still presents elevated levels of inorganic contamination even after 5 years following the event. Additionally, local climatic factors might pose as major drivers for bioaccumulation patterns in these animals, resulting in marked spatial and temporal fluctuations.

The Power of Stress: The Telo-Hormesis Hypothesis

Adaptative response to stress is a strategy conserved across evolution to promote survival. In this context, the groundbreaking findings of Miroslav Radman on the adaptative value of changing mutation rates opened new avenues in our understanding of stress response. Inspired by this work, we explore here the putative beneficial effects of changing the ends of eukaryotic chromosomes, the telomeres, in response to stress. We first summarize basic principles in telomere biology and then describe how various types of stress can alter telomere structure and functions. Finally, we discuss the hypothesis of stress-induced telomere signaling with hormetic effects.

A review of metal-induced effects on vitamins A, E and D3 in birds

Birds have been historically affected by metals and are considered powerful sentinels of environmental pollution. Some toxic elements (Pb, Cd, Hg, As) have been broadly studied in avian species and are well known for their accumulation capacity and deleterious effects, including alterations in vitamin levels. Vitamins A, E and D3 are fat-soluble nutrients involved in multiple physiological functions (e.g., immune function, vision, reproduction, growth and development). Publications reporting metal-induced effects on vitamins in birds are growing and, in some cases, results seem contradictory, making them difficult to interpret. Therefore, a clear view of the overall picture is needed. This mini-review article aims to compile relevant data and describe current knowledge on the effects of the most toxic elements (i.e., Pb, Cd, Hg, As) on vitamins A, E and D3 in birds. Although vitamins are diet dependent, they are strongly regulated and transformed in the organism, and metal-related disruption in their homeostasis may provoke alterations in different directions. Moreover, vitamin status and form in vivo is the result of complex interacting processes in the organism and metal exposure may produce cascade effects. Different factors that may contribute to the variable response of vitamins to metals in birds are discussed. Some final remarks and recommendations are provided for future studies. This mini-review shows an overview of the current knowledge in metal-induced alterations in vitamins of special concern for avian ecotoxicology, a research discipline facing important challenges in the coming years.

Bird Feces as Indicators of Metal Pollution: Pitfalls and Solutions

Bird feces are commonly used as a proxy for measuring dietary metal exposure levels in wild populations. Our study aims to improve the reliability and repeatability of fecal metal measurements and gives some recommendations for sampling. First, we studied levels of variation in metallic element (arsenic, calcium, cadmium, cobalt, copper, nickel, lead) concentrations: temporal variation within an individual, among siblings in a brood and among-brood/spatial variation. Second, we explored the variation caused by dual composition (urate vs. feces) of bird droppings. Two sets of fresh fecal samples were collected from pied flycatcher (Ficedula hypoleuca) nestlings living in a metal polluted area in summers 2017 (dataset 1) and 2018 (dataset 2). We found a great deal of temporal intra-individual variation in metal levels, suggesting that dietary exposure varied markedly in a short time scale (within a day). A sample from only one nestling per brood did not well describe the brood mean value, and we recommend that at least four siblings should be sampled. Brood level samples give relatively good temporal repeatability for most metals. For all the metals, the levels in the fecal portion were more than double to those in the urate portion. Since the mass proportion of urate in the bird droppings varied a great deal among samples, standardizing sampling, e.g., by collecting only the fecal part, would markedly reduce the variation due to composition. Alternatively, urate portion could be used for biomonitoring of internally circulated bioavailable metal.