Different paths, similar pressures: divergent drivers of genetic diversity despite convergent adaptive genomic responses to urbanisation in two oligolectic bee species

Urbanisation introduces novel ecological challenges that can impact biodiversity.Bees are vulnerable to these challenges, especially species with narrow ecological niches.To investigate how the urban environment influences the evolutionary dynamics of such taxa, we examined the genomic responses of two oligolectic solitary bee species, Andrena florea and Andrena vaga, along an urbanisation gradient in Braunschweig, Germany.Using whole-genome sequencing, we assessed genetic diversity, differentiation and structure, demographic trends and signatures of selection in both species.Although genetic differentiation was low in both species, it was significantly greater than zero, indicating subtle population structure across the urban gradient, with patterns consistent with isolation by distance.Genetic diversity in A. florea was positively associated with edge density, while in A. vaga it increased with semi-natural habitat.While urbanisation per se showed no clear effect on genetic diversity, both species, counterintuitively, exhibited a modest negative relationship with the proportion of urban green land uses, suggesting that not all urban green spaces are ideal for sustaining their populations.Demographic reconstructions revealed a historical bottleneck in A. florea 150 generations ago, followed by recovery, while A. vaga exhibited continuous expansion with little change in recent generations.Genotype-environment association analyses identified SNPs linked to urbanisation and functional annotation highlighted genes related to physiological, cognitive and behavioural traits.A subset of genes was shared by both species, indicating convergent adaptation to urbanisation.Our findings reveal divergent and parallel responses to urban environments and highlight the adaptive potential yet vulnerability of diet-specialised solitary bees in cities.