Reproductive Isolations In Seed Production And Germination Between Two Sister Desert Plants Pugionium Dolabratum And P. Cornutum (Brassicaceae)

Reproductive isolation is an important biological concept. It is a central aim of evolutionary biology to identify the critical barriers that restrict gene flow between recently diverged sister species, especially for those with overlapped distributions. In this study, we examined reproductive isolations in seed production and germination between Pugionium dolabratum and P. cornutum (Brassicaceae), parapatrically distributed in the deserts of the northwest China. Flowering times and flower visitors of two species are overlapped, suggesting weak temporal and pollinator isolations. However, cross hybridizations when one species serves as maternal donors produced low seed sets and hybrid seed had lower germination percentages. Especially, two species showed contrasted differences in seed germination percentage and rate in response to salinity stress and desert burials. Seeds of P. dolabratum preferring to fixed dunes germinated better under the strong salinity stress than those of P. cornutum occurring in the mobile deserts. However, seed germinations of two species after being buried by deep deserts revealed the reverse trends:P. cornutum had higher emergence percentage and rate of seedlings than P. dolabratum in the deep sand burials. These findings suggested that post-zygotic isolations due to ecological adaption to the differentiated habitats play a critical role in restricting genetic exchange of these two desert plants and maintain species integrity when they co-occur in the same locality and gene flow probably takes place through both pollens and seeds.