On urbanisation and birds : Insights from a molecular and physiological perspective

Sammanfattning: Urbanisation of natural habitats is rapidly intensifying and poses a potential global threat for wildlife. Thus, it is important to explore its impact on wildlife in order to understand the present and future threats and how resilient organisms are to them. Although many species decline in abundance or even disappear once an area is urbanised, some species, populations and/or individuals are able to succeed in this new environment. Indeed, marked phenotypic differences in behaviour, morphology and physiology have been demonstrated among species inhabiting urban environments. In this thesis, using birds as model organisms, I investigate the role of urbanisation and the implications of two important life-history traits; telomere dynamics and oxidative stress physiology. In addition, I studied the genomic structure of multiple urban and natural/semi-natural populations of great tit (Parus major), a common urban-dwelling species, in order to explore potential common signatures of selection and local adaptation to urban habitats. Regarding telomere dynamics, the results show that urban environments inflict an early-life detrimental effect on telomere length, probably through a combination of being exposed to multiple urban stressors and poorer diet. This early-life effect on telomere length had implications for survival, with strong selection against short telomere length individuals in the first year, especially in the urban environment. However, if the bird survives their first year, the urban environment does not seem to affect the telomere shortening more than the rural environment. Possibly, some of the urban factors such as supplementary feeding, higher temperatures or lower predation risk, may outweigh the costs of being exposed to different stressors (e.g. air and noise pollution or artificial light at night).With respect to oxidative stress physiology, we found that in four common urban passerine species, the plasma antioxidant capacity was positively correlated with increases in urbanisation and air pollution intensity (i.e., NOx exposure estimates). Although, their response to urbanisation/NOx was similar, there were significant differences between the four species in absolute levels, suggesting different reaction norms to urbanisation/NOx or different capacities in the up-regulation of the antioxidant physiology. Indeed, and despite the increase in the antioxidant capacity, one of the species, the tree sparrow (Passer montanus), had increased levels of protein carbonyls (oxidative damage biomarker), but only in relation to NOx exposure. This suggests that this species is more sensitive to pollution. Furthermore, the latter result highlights the importance to study markers of oxidative stress across species and in the same environments, in order to understand how urban environmental stress affects species differently. Finally, our genomic analysis of multiple great tit urban populations reveals that despite the overall low genetic differentiation, some loci diverged in relation to urbanisation. This implies that parallel evolution of a few key genes may play an important role for adaption to the urban environment. In summary, the results presented in this thesis shed light and offer new perspectives in the emerging field of urban ecology, particularly for bird urban ecology, but also regarding life-history variation and the potential mechanisms involved in shaping phenotypic traits to novel environmental stressors.