Pollination in Ephedra (Gnetales)

University dissertation from Stockholm : Department of Ecology, Environment and Plant Sciences, Stockholm University

Abstract: Pollination, i.e., the transport of male gametophytes to female gametophytes, can occur with biotic or abiotic vectors and is necessary for fertilization and completion of the lifecycle in all seed plants. Insect pollination and the co-evolution between angiosperms and insects have during the last century been discussed as one possible solution to Darwin’s abominable mystery and an important explanation for the relatively abrupt turn-over from a vegetation dominated by gymnosperms to a vegetation dominated by angiosperms in the Cretaceous. Insect pollination is, however, a much older phenomenon that can be traced back to the Devonian, but is it an ancestral trait that has been lost in many seed plant groups, or has it originated multiple times in parallel? These questions have to be addressed in a phylogenetic framework comprising extant and extinct seed plant groups. The Gnetales are constantly in focus in studies of seed plant phylogeny, probably because they have repeatedly been suggested, and refuted, to be the closest living relatives of angiosperms. The order consists of three genera, Gnetum, Welwitschia and Ephedra, of which the former two have long been known to be insect pollinated. Pollination biology in Ephedra has, however, been poorly studied and understood. In this thesis pollination mechanisms in Ephedra (Gnetales) are investigated by field experiments and observations (Paper I) and aerodynamic simulations and studies of pollen morphology (Paper II). The results show that there are multiple pollination mechanisms within this otherwise morphologically and ecologically uniform genus. Further, in contrast to what has often been assumed, insect pollination is shown to be ancestral in the Gnetales and not a derived feature that has evolved within the group. Using this new information on pollination biology in the Gnetales and data from the literature, I explore evolution of pollen morphology and pollination mode in seed plants.