Urban Life Shapes Genetic Diversity in the Green Anole, Anolis carolinensis.

Abstract

Urbanisation presents unique environmental pressures that drive rapid evolutionary adaptations, particularly in species inhabiting fragmented and anthropogenised landscapes. In this study, we investigate the genomic differentiation between urban and non-urban populations of Anolis carolinensis, focusing on two main aspects: (1) the effect of habitat fragmentation on inbreeding and mutational load and (2) genomic adaptation to the urban habitat. We found that urban populations can exhibit a reduced mutational load, which is a direct consequence of systemic inbreeding. Using genome-wide scans of selection and analyses of genetic diversity, we identify key genomic regions exhibiting significant divergence between urban and non-urban populations. These regions are enriched for genes associated with immunity, behaviour and development, suggesting that urban adaptation is polygenic and involves traits related to stress response, locomotion and thermoregulation. Scans for association with the urban environment reveal a large genomic region in chromosome 2 encompassing the HOXC gene cluster. We also detect a signal of both association and increased differentiation on chromosome 1 in a region previously identified as a candidate for convergent adaptation in another Anolis species, A. cristatellus. Although evidence for convergent evolution at the gene level remains limited, potential signatures of urban adaptation in loci involved in immune response, locomotion and behaviour support the hypothesis that urban environments exert similar selective pressures across species. These results provide evidence for redundancy and polygenic adaptation and highlight the complexity of urban evolution. Future work with denser population sampling and time-series data will be essential to confirm the role of urban selective pressures and track the genetic dynamics of urban populations over time.