Metal pollution drives earthworm biodiversity in urban lawns.

Urban soils represent hotspots of metallic trace elements (MTEs) pollution. Despite the critical impact of soil organisms on soil ecosystem services, there is limited understanding regarding the effects of MTE levels in urban soils on these organisms. This is particularly surprising considering that earthworms, key organisms for soil ecosystems, are commonly used in MTE toxicity tests. This research investigates the impact of MTE pollution on earthworm communities in lawns within the city of Paris. In this study, we sampled a comprehensive array of earthworm communities, totalling 965 individuals from 13 distinct species belonging to Lumbricus, Aporrectodea, Allolobophora and Octolasion genera. These communities were collected from three different locations within 18 parks. At these sites, we assessed the concentrations of eight metals and metalloids in the soil (As, Cd, Cr, Cu, Zn, Ni, Pb and Hg), along with selenium concentrations and eight fundamental soil parameters, to examine the association between earthworm communities and soil attributes. Median MTE concentrations exceeded recommended statutory limit values by approximately 20 % (0.6 mg/kg Cd), 30 % (36.8 mg/kg Cu), 40 % (122.0 mg/kg Zn), and up to 90 % (0.6 mg/kg Hg and 99.7 mg.kg Pb). Nevertheless, these concentrations exhibited considerable variability both between and within parks, correlating with variations in earthworm community structures. Specifically, our results highlight that Cu concentrations in the soil explain about 6 % of the variation in the assemblage of earthworm species. Our findings underscore the importance of considering MTE pollution levels to enhance our comprehension of earthworm distribution in urban environments and its effects on the ecosystem services provided by urban lawns.

Virtual reality validation of naturalistic modulation strategies to counteract fading in retinal stimulation.

Objective. Temporal resolution is a key challenge in artificial vision. Several prosthetic approaches are limited by the perceptual fading of evoked phosphenes upon repeated stimulation from the same electrode. Therefore, implanted patients are forced to perform active scanning, via head movements, to refresh the visual field viewed by the camera. However, active scanning is a draining task, and it is crucial to find compensatory strategies to reduce it.Approach. To address this question, we implemented perceptual fading in simulated prosthetic vision using virtual reality. Then, we quantified the effect of fading on two indicators: the time to complete a reading task and the head rotation during the task. We also tested if stimulation strategies previously proposed to increase the persistence of responses in retinal ganglion cells to electrical stimulation could improve these indicators.Main results. This study shows that stimulation strategies based on interrupted pulse trains and randomisation of the pulse duration allows significant reduction of both the time to complete the task and the head rotation during the task.Significance. The stimulation strategy used in retinal implants is crucial to counteract perceptual fading and to reduce active head scanning during prosthetic vision. In turn, less active scanning might improve the patient's comfort in artificial vision.

Replicated, urban-driven exposure to metallic trace elements in two passerines.

While there are increasing examples of phenotypic and genotypic differences between urban and non-urban populations of plants and animals, few studies identified the mechanisms explaining those dissimilarities. The characterization of the urban landscape, which can only be achieved by measuring variability in relevant environmental factors within and between cities, is a keystone prerequisite to understand the effects of urbanization on wildlife. Here, we measured variation in bird exposure to metal pollution within 8 replicated urbanization gradients and within 2 flagship bird species in urban evolutionary ecology: the blue tit (Cyanistes caeruleus) and the great tit (Parus major). We report on a highly significant, positive linear relationship between the magnitude of urbanization-inferred as either tree cover, impervious surface cover, or an urbanization score computed from several environmental variables, and copper, zinc and lead concentrations in bird feathers. The reverse relationship was measured in the case of mercury, while cadmium and arsenic did not vary in response to the urbanization level. This result, replicated across multiple cities and two passerine species, strongly suggests that copper, zinc, lead and mercury pollution is likely to trigger the emergence of parallel responses at the phenotypic and/or genotypic level between urban environments worldwide.

Growing in the city: Urban evolutionary ecology of avian growth rates.

INTRODUCTION: Rapid environmental change driven by urbanization offers a unique insight into the adaptive potential of urban-dwelling organisms. Urban-driven phenotypic differentiation is increasingly often demonstrated, but the impact of urbanization (here modelled as the percentage of impervious surface (ISA) around each nestbox) on offspring developmental rates and subsequent survival remains poorly understood. Furthermore, the role of selection on urban-driven phenotypic divergence was rarely investigated to date. METHODS AND RESULTS: Data on nestling development and body mass were analysed in a gradient of urbanization set in Warsaw, Poland, in two passerine species: great tits (Parus major) and blue tits (Cyanistes caeruleus). Increasing levels of impervious surface area (ISA) delayed the age of fastest growth in blue tits. Nestling body mass was also negatively affected by increasing ISA 5 and 10 days after hatching in great tits, and 10 and 15 days in blue tits, respectively. High levels of ISA also increased nestling mortality 5 and 10 days after hatching in both species. An analysis of selection differentials performed for two levels of urbanization (low and high ISA) revealed a positive association between mass at day 2 and survival at fledging. DISCUSSION: This study confirms the considerable negative impact of imperviousness-a proxy for urbanization level-on offspring development, body mass and survival, and highlights increased selection on avian mass at hatching in a high ISA environment.

The association between stressors and telomeres in non-human vertebrates: a meta-analysis.

Animal response to stressors such as harsh environmental conditions and demanding biological processes requires energy generated through increased mitochondrial activity. This results in the production of reactive oxygen species (ROS). In vitro and some in vivo studies suggest that oxidative damage of DNA caused by ROS is responsible for telomere shortening. Since telomere length is correlated with survival in many vertebrates, telomere loss is hypothesised to trigger cellular ageing and/ or to reflect the harshness of the environment an individual has experienced. To improve our understanding of stress-induced telomere dynamics in non-human vertebrates, we analysed 109 relevant studies in a meta-analytical framework. Overall, the exposure to possible stressors was associated with shorter telomeres or higher telomere shortening rate (average effect size = -0.16 ± 0.03). This relationship was consistent for all phylogenetic classes and for all a priori-selected stressor categories. It was stronger in the case of pathogen infection, competition, reproductive effort and high activity level, which emphasises their importance in explaining intraspecific telomere length variability and, potentially, lifespan variability. Interestingly, the association between stressor exposure and telomeres in one hand, and oxidative stress in the other hand, covaried, suggesting the implication of oxidative stress in telomere dynamics.

Pigeon odor varies with experimental exposure to trace metal pollution.

Trace metals are chemical pollutants that have well-known noxious effects on wildlife and that are current major environmental issues in urban habitats. Previous studies have demonstrated their negative (e.g. lead) or positive (e.g. zinc) effects on body condition, immunity and reproductive success. Because of their effects on condition, trace metals are likely to influence the production of condition-dependent ornaments. The last decade has revealed that bird odors, like mammal odors, can convey information on individual quality and might be used as secondary sexual ornaments. Here, we used solid-phase microextraction headspace sampling with gas chromatography-mass spectrometry to investigate whether plumage scent varied with experimental supplementation in lead and/or zinc in feral pigeons. Zinc supplementation (alone or in combination with lead) changed the proportion of several volatiles, including an increase in the proportion of hydroxy-esters. The production of these esters, that most likely originate from preen gland secretions, may be costly and might thus be reduced by stress induced by zinc deficiency. Although lead is known to negatively impact pigeon condition, it did not statistically affect feather scent, despite most of the volatiles that increased with zinc exposure tended to be decreased in lead-supplemented pigeons. Further studies should evaluate the functions of plumage volatiles to predict how trace metals can impact bird fitness.

Do trace metals select for darker birds in urban areas? An experimental exposure to lead and zinc.

Trace metals from anthropogenic activities are involved in numerous health impairments and may therefore select for detoxification mechanisms or a higher tolerance. Melanin, responsible for the black and red colourations of teguments, plays a role in metal ion chelation and its synthesis is positively linked to immunity, antioxidant capacity and stress resistance due to pleiotropic effects. Therefore, we expected darker birds to (1) store higher amounts of metals in their feathers, (2) maintain lower metal concentrations in blood and (3) suffer less from metal exposure. We exposed feral pigeons (Columba livia) exhibiting various plumage darkness levels to low, but chronic, concentrations of zinc and/or lead, two of the most abundant metals in urban areas. First, we found negative and positive effects of lead and zinc, respectively, on birds' condition and reproductive parameters. Then, we observed positive relationships between plumage darkness and both zinc and lead concentrations in feathers. Interestingly, though darker adults did not maintain lower metal concentrations in blood and did not have higher fitness parameters, darker juveniles exhibited a higher survival rate than paler ones when exposed to lead. Our results show that melanin-based plumage colouration does modulate lead effects on birds' fitness parameters but that the relationship between metals, melanin, and fitness is more complex than expected and thus stress the need for more studies.