Phenotypic plasticity and pollinator-mediated selection jointly influenced floral differentiation in an alpine primrose

Both pollinator-mediated selection and phenotypic plasticity play important roles in the flower diversification under different spatiotemporal environments. However, the effects of natural selection and phenotypic plasticity on the process of flower evolution have rarely been collectively studied. In this study, two populations of Primula sikkimensis (GLL and SJL populations) were hand-pollinated to evaluate selection for four floral traits. In addition, reciprocal transplant experiments were conducted to detect the degree of plasticity of these floral traits in both populations. We found significant differentiation of floral traits between populations, and some of them varied between years. Pollinator-mediated selection contributed to net selection on traits, which varied in space and time. Moreover, these four floral traits showed strong plasticity in individuals of the GLL population but weak plasticity in the SJL population. Finally, the degrees of phenotypic plasticity were positively correlated with the variability of net selection and pollinator-mediated selection. Our findings reveal that both phenotypic plasticity and pollinator-mediated selection concurrently influence flower differentiation, yet strong plasticity has the potential to weaken the effects of selection.