Historical and Contemporary Genetic Structure Reveals Recent Fragmentation Without Loss of Diversity in Mediterranean House Sparrow Populations

Understanding how human-modified environments shape long-term genetic diversity is crucial for conservation, particularly in species experiencing declines. The House Sparrow Passer domesticus has declined markedly across Europe, yet its long-term genetic dynamics remain poorly understood in Mediterranean landscapes. We assessed spatiotemporal patterns of neutral genetic variation by integrating contemporary samples from 13 populations along an agricultural–urban gradient in Catalonia (NE Spain) with historical museum specimens (1919–1950). Using twelve microsatellite loci, we quantified changes in genetic diversity, population structure, and demographic signals. Historical populations were genetically homogeneous, reflecting an ancestral state of high regional connectivity. In contrast, contemporary populations exhibited increased genetic structuring, marginal increases in inbreeding coefficients, and heterozygote deficiencies, forming multiple clusters not associated with habitat categories. Isolation-by-distance was significant in contemporary populations (R2 = 11.1