Ephedra trait evolution and plant-animal interactions

Dispersal syndromes – The New World species of Ephedra exhibit three distinct dispersal syndromes related to dispersal by birds (and lizards), wind and rodents associated with distinct strobili morphologies. Based on our analyses speciation events in the New World coincided with the expansion of arid habitats in this region and we suggest that the bird dispersal syndrome is related with higher rates of climatic niche evolution for all variables used, including aridity index, mean annual temperature and mean annual precipitation. Distribution ranges were correlated with niche breadth, they were however not significantly different between dispersal syndromes. Species inhabiting the extremely arid regions on niche axes had narrower niche breadths. We conclude that species whose seeds are dispersed by birds have colonized a broader set of habitats and that those with wind and rodent dispersal syndromes might have promoted the colonization of more arid environments (Loera et al. 2015).

Dispersal_m

Three dispersal syndromes in Ephedra with distinct strobili morphologies from left to right: animal dispersal by birds or lizards (zoochory), wind dispersal (anemochory) and rodent dispersal (zoochory).

Video of Ephedra trifurca wind dispersal in Sonoran desert scrub near Madera Canyon, Arizona.

Pollination biology and pollination droplets – While wind pollination is the prevalent mode of pollination in extant Gnetales  and most gymnosperms, field observations and experimental studies have documented insect visitation in all three genera of the Gnetales. Just as insect visitation, bisexual cones also have been documented in all three genera and may represent the ancestral condition.  Chemical analysis of pollination drops in 13 species representing the main lineages of extant gymnosperms (Ginkgo, cycads, Coniferales, and Gnetales) reveals a correlation between wind or insect pollination and total sugar content, fructose concentration, proline and amino acid concentration (Nepi et al., 2016 in review). Droplets of insect-pollinated or ambophilous gymnosperms (Zamia furfuracea, Welwitschia mirabilis, Gnetum gnemon, Ephedra fragilis) and those of Ginkgo biloba and Ephedra minuta, whose pollination mode is unclear, have higher levels of carbohydrates, lower levels of amino acid, and specific sugars and amino acids profiles than gymnosperms shown to be wind-pollinated in experimental studies. Most probably, insects shifted from fluid feeding on the ovular secretions of gymnosperms to feeding on angiosperm nectar as the latter became abundant and species rich (Nepi et al., 2016 in review).

Figure7ants

Ant visitation on Ephedra trifurca in the Sonoran Desert, Arizona. A, Ovulate strobilus with pollination drop formation at the micropylar tube. B, Ant of Myrmecocystus cf. mimicus Wheeler, 1908 feeding on pollination droplet of ovulate cone in E. trifurca. C, Myrmecocystus cf. mimicus foraging in staminate cones of E. trifurca.