Pollinator-driven speciation week continues, with Floral adaptation to local pollinator guilds in a terrestrial orchid, a paper by Sun, Gross and Schiestl. The star is the orchid Gymnadenia odoratissima, and orchid found in lowland temperate Europe and up in the mountains. It flowers between June and mid-August. Unlike the orchids yesterday, these flowers offer a food reward as well as a strong scent.
The study examined a number of lowland and mountain orchids in Switzerland. A team of patient observers with nets watched to see what visited the orchids in all the locations, during the day and night. In the lowland orchids they found visitors to b butterflies/moths and beetles. In the mountains there were also Diptera, flies. There wasn’t much overlap between the species of pollinators.
The next stage was to start transferring populations of orchids. The obvious way to move the orchids was to change their altitude, to move the lowland plants to the mountains and bring the highland plants down. Sun et al. also moved some samples along the same altitude. This helped provide another check on how the orchids coped with being moved. What they found was that the mountain orchids were fairly successful in the lowlands, but the lowland plants did comparatively badly in the mountains.
However, the transferred mountain orchids did much worse in the lowlands than if they’d stayed put. Sun et al. point out one of the things the lowlands lack are Empidid flies. Fly pollination is an important factor for plants at higher altitudes. The lowland plants weren’t much less successful when they moved. It suggests that the mountain plants have adapted their flowers to take advantage of the flies in a way that the lowland plants haven’t. For example the chemicals in the scents of the flowers are different between the lowland and mountain plants. The mountain flowers also tended to be paler, and this is attractive to moths, who are more common in the uplands than the lowlands. There are more butterflies in the lowlands, who pollinate by day and so darker flowers may be comparatively more attractive here.
What the experiments show is that the changes in floral display aren’t simply products of altitude. It seems that G. odoratissima is altering its flowers in reaction to the local pollinator guilds. You can pick up this paper from Annals of Botany.