| dc.description.abstract | Interspecific hybridization has intrigued evolutionary biologists since Darwin s time. New genetic combinations can arise from hybridization, leading to offspring sometimes able to adapt to different niches than their parental species. I wanted to study beak morphology in Italian sparrow and house sparrow in a contact zone in the Alps, where they interbreed. This contact zone is situated in an ecotone, so I also investigated if climatic factors could affect beak size or beak shape. I used a geometric morphometrics approach, with landmarks from photos, to investigate if there are differences between the two species and their hybrids in this zone. The results revealed a pattern of intermediacy for the hybrids in beak size and in one dimension of beak shape. Another dimension of beak shape is transgressive in hybrids, that is outside the range of their parents. I show that there is a significant association between genetic admixture and beak size and also the first dimension of beak shape. Moreover, beak size variation is also significantly associated with environmental variation. The transgressive dimension of beak shape was also affected by environment, but not by genetic admixture. This may indicate that different factors and selection pressures affect beak morphology, including environment and genetic admixture. Cline analysis was used to infer selection on the beak. Steep clines were found for beak size and the intermediate dimension of beak shape; beak size having the steepest cline. Generation time estimates, assuming neutral diffusion, based on the widths of the cline analysis, were much lower than the likely age of the hybrid zone, indicating strong selection on beak size and shape in the hybrid zone. Selection coefficients indicate low fitness for intermediates. Overall, my results imply strong selection on beak size and shape. I discuss whether these traits may be involved in reproductive isolation between the Italian sparrow and house sparrow. | eng |