Phenotypic plasticity and genetic diversity in Poa annua L-[Poaceae] at Crozet and Kerguelen Islands (subantarctic)

The widely distributed grass, Poa annua, is one of the most common alien sp ecies in the subantarctic islands. The historical events of its introductio n remain generally unknown, as well as the evolutionary consequences of its colonisation in these remote environments. Populations from the Crozet arc hipelago and Kerguelen Islands were compared in terms of morphology, cytoge netics and enzyme polymorphism. Seeds from natural populations were also so wn in an experimental garden in France to test phenotypic plasticity. This preliminary study demonstrated the high phenotypic plasticity in P. annua i n the French subantarctic islands. This plasticity and allotetraploidy coul d be important factors which reinforce the colonising capacities of P. annu a. Our results revealed the low genetic diversity of the populations analys ed, which could be related to the founding effect or to the fragmentation o f the populations.