Reproductive biology of South American Ephedra

Abstract

Ephedra (Gnetales) comprises approximately 50 species distributed in deserts world-wide, with almost all South American species occurring in arid and semi-arid regions of Argentina. Ephedra are presumed ancestrally insect pollinated, with a shift to wind pollination occurring early in its diversification. While the prevailing assumption is that most extant Ephedra are anemophilous, field experiments on Mediterranean species have shown insect pollination in at least one species and ambophily (wind and insects) in two others. Here, we studied for the first time the reproductive biology of four argentinian representatives of Ephedra (E. triandra, E. chilensis, E. americana and E. multiflora) of Northwest Argentina, covering a range of habitats from ?Monte? desert (1,300 m a.s.l.) to Puna or ?Alto Andino? biome (above 4,000 m). We combined field observations and experimental studies on pollination and seed dispersal mode with plant morphology observations. Our preliminary results show that female cones of E. triandra, E. americana and E. chilensis are inconspicuously green at the pollination stage. We documented pollination droplets (sugary secretions) on female cones of E. triandra and E. americana. Male cones display brightly yellow microsporangiophores at anthesis but lack pollination droplets. Insect visitors included ants, wasps, coleopterans and flies as potential pollinators on female cones. Pollen traps on E. triandra female plants shows that pollen is effectively transported by wind. Exclusion experiments and field observations on E. triandra showed that ants were almost the exclusively consumers of the pollination droplets of female cones and had a positive effect on seed set, which was significantly higher compared to the insect- exclusion bags (circa 95 vs.70%). Pollen grains were found on the ants? bodies, with no reduction in pollen viability, thus suggesting ants as secondary pollinators of this species. The Puna species E. multiflora is the only with dry, winged bracts, which suggest wind-dispersal, while the others have fleshy, red bracts when mature. Seed dispersal data from trail cameras showed that E. triandra and E. chilensis seeds are consumed by birds, possums, and rodents. At least two ant species carried the seeds of E. triandra to their nests. Seeds of E. chilensis were found on bird droppings, suggesting bird dispersal as well. Our study provides the first field-based results on reproductive biology of south American Ephedra in their natural habitat, and hence we hope it will contribute to ongoing conservation efforts of the sole gymnosperm of arid and semi-arid ecosystems of Argentina