How does urbanisation affect wildlife in cities? I am investigating this key research question by working on great tit (Parus major) and blue tit (Cyanistes caeruleus) populations breeding in a gradient of urbanisation in the city of Warsaw in Poland. Five hundred nestboxes are studied in a continuum of urban to rural conditions, for which tree cover as well as noise, light and chemical pollution are determined for each nestbox. I am investigating the link between oxidative stress, a physiological index of organismal health, and the degree of urbanisation. In particular, I am currently estimating the extent to which trace metal exposure is linked to urbanisation-induced oxidative stress in great and blue tit populations. Because oxidative stress and trace metal exposure are likely to affect great and blue tits through several physiological pathways, I am estimating their impact on great and blue tit health by measuring bird body mass and body condition, telomere length (telomeres protect the end of a chromosome from deterioration, and their length has been associated with the rate of ageing in animals), reproductive success and survival. Finally, I am asking whether urbanisation-induced physiological changes identified in this study have a genetic basis. Understanding the nature of these processes (acclimatization vs. genetic based differences) is of fundamental interest in evolutionary biology and conservation biology alike. Such knowledge will also be of great value in making accurate forecasts about which animals may settle and thrive in cities.

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

(in collaboration with Szymon Drobniak & Marta Szulkin)

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 carried out an exhaustive search of the studies testing the association between stressor exposure and telomeres and analysed their results in a meta-analytical framework. For the first time, this comprehensive study highlights an overall significantly negative correlation between stressor exposure and telomeres (both telomere length and shortening). Importantly, this association is consistent for all phylogenetic classes, and for all a priori- selected stressors, thus confirming that stressful conditions are a driver of telomere shortening. Of particular interest, it identifies key environmental conditions and life history traits correlated with telomere length and dynamics: pathogen infection, competition, reproduction and activity. It also shows that stressor exposure-telomeres and stressor exposure-oxidative stress associations covary, suggesting that the link between stressor exposure and telomeres might be mediated by oxidative stress. Finally, it raises important methodological considerations for studying stress-induced telomere dynamics, which we believe will constitute a helpful guideline for future studies in this field.

This work has been published in Ecology Letters (Chatelain et al. 2019 Ecology Letters). Overall, our article gives an overview of stress-induced telomere dynamics, together with a rational and synthetic explanation of the proximal physiological mechanisms involved. 

Nutshell summary:

• We extracted data on the association between stressor exposure and telomeres from 109  studies and analysed them in a meta-analytical framework.
• For the first time, this comprehensive study highlights an overall significantly negative correlation between stressor exposure and telomeres.
• From 25 papers that also included data on oxidative stress, our study also suggests that the link between stressor exposure and telomeres might be mediated by oxidative stress. 

Urban metal pollution explains variation in reproductive outputs in great tits and blue tits

(in collaboration with Sylvie Massemin, Sandrine Zahn, Eliza Kurek, Ewa Bulska & Marta Szulkin)

It is regularly reported that avian reproductive outputs are reduced in urban areas, yet the underlying reasons for discrepancies between urban and natural habitats are to date poorly explained. To address this knowledge gap, we tested whether the reproductive outputs of wild great tit (Parus major) and blue tit (Cyanistes caeruleus) populations in Warsaw (Poland) correlated with the concentrations of six main metallic/metalloid trace elements (MTEs; copper, zinc, lead, cadmium, arsenic and mercury) in three types of biological material pertaining to avian reproduction: nestling feathers, nest material and nestling droppings. For the first time, our study highlights consistent negative effects of copper and arsenic concentrations in nestling feathers on fledging success and nestling mass in both great tits and blue tits. Fledging success was also negatively correlated with cadmium and lead concentrations in nestling droppings. Importantly, while the relative proportions of each MTE were equivalent between the three biological materials, reproductive success correlated better with MTE concentrations in nestling feathers than in the two other materials; this result suggests that MTE absorption would explain part of the variation in individual fitness and emphasises the relevance of using nestling feathers for investigating the effects of MTE exposure on nestlings of hole-nesting birds. Altogether, our results suggest that urban MTE pollution likely contributes to the differences in reproductive outputs observed between tit populations living in urban and more natural environments.

This work has been recently published in Science of the Total Environment (Chatelain et al. 2021 STOTEN). 

Nutshell summary:

• We measured MTEs in three biological materials: nestling feathers and droppings, and the nest material.
• We measured how MTEs exposure affects nestling survival, mass and telomere length.
• Cu, As, Pb and Cd negatively affect great tit and blue tit reproductive success.