Abstract It is broadly assumed that polyploidy success is due to an increase in fitness associated with whole genome duplication due to higher tolerance to stressful conditions. In agreement, several theoretical models found that, among other factors, a better tolerance to new environmental conditions can promote polyploidy establishment. These models, however, often made strong hypotheses, for example considering that diploids cannot adapt to new conditions, or that unreduced gametes production is not a limiting factor and that it is of a fixed quantity. In this paper, we challenged some of these hypotheses. We developed a theoretical model in which we modeled the joint evolution of a quantitative trait under selection and the production of unreduced gametes, this trait also being a quantitative trait; both traits were pleiotropically linked. We followed the adaptation of initially diploid populations to a new environment to which neo-tetraploid individuals were directly adapted. The generation of these autotetraploid individuals was enabled by the genetic production of unreduced gametes and by the environmental change modifying the average production of these gametes. We found that for realistic values of unreduced gametes production, adaptation to new environmental conditions was mainly achieved through adaptation of diploids to the new optimum rather than the fixation of newly adapted tetraploid individuals. In broader parameter sets, we found that the adaptation process led to mixed-ploidy populations, except when the populations were swamped with unreduced gametes, and that pleiotropy and environmental effects favored the co-existence of both cytotypes.