Telomere dynamics and lifetime fitness in a migratory passerine bird

Telomeres are nucleoprotein complexes located at the ends of eukaryotic chromosomes which ensure stability to the entire genome. Due to the inability of DNA polymerase to fully replicate linear DNA, they shorten at each cell division. In addition, this shortening is enhanced by detrimental environmental conditions and/or high metabolic activities through an increase of oxidative stress. When telomeres reach a threshold length, they lose their functionality causing either cell senescence or apoptosis, with negative consequences for organismal functions and performances. Therefore, an age-related decrease in telomere length is expected, as it has already shown in several vertebrates, but an increase in telomeres length with age has been also seldom documented. However, most studies have been conducted in laboratory conditions, and those realized on natural populations are few, based on small samples and provide contrasting results. This study relied on a large dataset, resulting from a multi-year data collection, which include information of the entire life of free-living adult barn swallows (Hirundo rustica) under natural and sexual selection regimes. Relative telomere length (RTL) has been estimated following a well-established protocol which involves DNA extraction from red blood cells and subsequent qPCR. Firstly, the study aimed at evaluating the telomere dynamics over the entire life of these birds. Another purpose was to investigate how telomere dynamics are related to individual lifetime fitness (i.e. reproductive success and individual survival/longevity). Furthermore, the study tested the relation between telomere dynamics and the expression of secondary sexual traits under directional selection in the study population (outermost tail feathers) to better understand the potential role of telomeres in sexual selection processes. Finally, we also evaluated some possible environmental effects on RTL and its inter-annual, inter-individual and inter-colony variation. These invaluable data gave us the extraordinary opportunity to test the eco-evolutionary role of telomeres in natural populations.