Temporal analysis of genetic variability and extra-pair paternity in an alpine population of Rock Sparrow (Petronia petronia)

Populations at the margins of a species’ distribution range face several challenges including small population size, a higher risk of inbreeding, and reduced genetic variability. In such populations, extra-pair paternity (EPP) has been hypothesized as a potential mechanism to counteract these limitations by increasing offspring heterozygosity. To complicate matters further, climate warming may further interact with these dynamics by altering breeding phenologies and mating strategies. The Alpine population of the rock sparrow (Petronia petronia) residing in the Upper Susa Valley (Turin, Italy) exhibits lower genetic variability and EPP rates up to three times higher than those reported for other populations, located near the center of the species’ European range. The Susa Valley has also undergone a progressive warming since the 1990s, with a consequent extension of the Rock sparrows’ breeding season, making it an ideal candidate for assessing long term trends in genetic variability and mating behaviour under a climate change. In this thesis I have analyzed DNA from 164 adults sampled in 2025 and assigned paternity to 318 chicks born in 2024-2025 with microsatellite markers. Measure of genetic variability, heterozygosity and EPP rates were compared with data from late 1990s and early 2000s. We detected no change in the female choice of extra-pair partners over time in terms of genetic similarity, possibly indicating that EPP is unlikely to function as a strategy to increase heterozygosity of extra-pair offspring in this population. At the same time, we also observed positive but non-significant time trends in both polygyny and extra-pair broods numbers. Taken together, this evidence suggests that the rock sparrow’s mating system in the Susa Valley reflects a dynamic balance among several ecological and climate related influences.