Abstract
Urbanization is a growing concern challenging the evolutionary potential of wild populations by reducing genetic diversity and imposing new selection regimes affecting many key fitness traits. However, genomic footprints of urbanization have received little attention so far. Using RAD sequencing, we investigated the genomewide effects of urbanization on neutral and adaptive genomic diversity in 140 adult great tits Parus major collected in locations with contrasted urbanization levels (from a natural forest to highly urbanized areas of a city; Montpellier, France). Heterozygosity was slightly lower in the more urbanized sites compared to the more rural ones. Low but significant effect of urbanization on genetic differentiation was found, at the site level but not at the nest level, indicative of the geographic scale of urbanization impact and of the potential for local adaptation despite gene flow. Gene–environment association tests identified numerous SNPs with small association scores to urbanization, distributed across the genome, from which a subset of 97 SNPs explained up to 81% of the variance in urbanization, overall suggesting a polygenic response to selection in the urban environment. These findings open stimulating perspectives for broader applications of high‐resolution genomic tools on other cities and larger sample sizes to investigate the consistency of the effects of urbanization on the spatial distribution of genetic diversity and the polygenic nature of gene–urbanization association.
Highlights
Humans substantially modify natural ecosystems, especially since the industrial revolution (Vitousek, Mooney, Lubchenco, & Melillo, 1997)
For the first time in a passerine bird, this study shows a small yet significant effect of urbanization on genomewide diversity and differentiation
This result contrasts with the relatively high effects of urbanization on genetic diversity and differentiation observed for terrestrial animals with lower dispersal capacities compared to birds (e.g., Peromyscus spp.; Munshi-South et al, 2016) and with the results obtained previously for great tits in Barcelona City (Björklund et al, 2010)
Summary
Humans substantially modify natural ecosystems, especially since the industrial revolution (Vitousek, Mooney, Lubchenco, & Melillo, 1997). Urbanization affects habitats, notably resulting in their loss, modification, or fragmentation (Crooks & Sanjayan, 2006). Urbanization results in chemical, noise, and light pollution, altered temperatures, novel epidemics, predation risks, all in all resulting in the modification of species assemblage and demography (Aronson et al, 2014; Galbraith, Jones, Beggs, Parry, & Stanley, 2017; Shryock, Marzluff, & Moskal, 2017; Vincze et al, 2017), phenotypic traits (Alberti et al, 2017; Biard et al, 2017; Suárez- Rodríguez, Montero-Montoya, & Macías Garcia, 2017), and evolutionary dynamics (Alberti, 2015; Anderies, Katti, & Shochat, 2007; Hendry, Gotanda, & Svensson, 2017). Urbanization generally results in dramatic local biodiversity declines as a lot of species avoid or are unsuccessful in urban environments, other species are able to cope
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