| ||||||||||||||||||||||
ANITA and the neater pollen eater
The “ANITA grade” of extant plant families is a group that branched very early from the main angiosperm lineage. One feature of the early evolution of flowering plants that is widely accepted is the importance of mutualistic interactions with insects; it is one of those interactions that has been studied by Yuan et al. (Beijing, China and New Orleans, USA; pp. 451-460). Since the Schisandraceae is an ANITA grade family with a little-known pollination biology, the authors have focused on Schisandra henryi. This species is dioecious but the male and female flowers, hanging on slender pedicels, are very similar. Both male and female flowers lack fragrance and no potentially fragrant molecules were detected by GCMS. Furthermore, no nectar is produced and the flowers are not thermogenic. It is therefore likely that pollinators are attracted by visual cues alone. The small size of the floral orifice prevents most insects entering the flowers. The sole pollinators are females of a gall midge in the genus Megommata. Their reward for visiting male flowers is pollen, some of which is eaten by the gall midges. However, female flowers, which the female Megommata also visit, obviously produce no pollen. Essentially, this has every appearance of a deception strategy by the plant: the very similar flower appearance and greater abundance of male flowers (outnumbering female flowers by at least 3 : 1) means that insects will visit female flowers “by mistake” and thus transfer pollen. This study has thus yielded several novel results. The Megommata species was previously unknown; it is the only predacious gall midge known to eat pollen. Restriction of pollination to a single species contrasts with more generalist pollination strategies in other members of the ANITA grade. Although deceit is quite widespread, it seems likely to have appeared early in angiosperm evolution.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
| ||||||||||||||||||||||