Impact of pollinator shifts on mating systems and population genetic diversity in a Neotropical plant group

Pollinator shifts, shifts in the functional group of a plant species’ pollinator, are believed to be triggered by changes in pollinator quantity and pollinator quality. In tropical systems, shifts from bee pollination in lowland species to vertebrate pollination (humming-birds, bats) in montane species seem to be common as the activity of vertebrates is less affected by adverse weather conditions. Such shifts can have consequences for the plant species’ mating systems as well as for population genetic structure and diversity. Experimental studies support the hypothesis that birds and bats are more efficient pollinators than bees, transferring larger amounts of pollen and capable of spanning larger distances between plant individuals. However, the impact of different functional pollinator groups on population genetic diversity is still largely unknown.
We chose the Neotropical tribe Merianieae (Melastomataceae), harbouring bee, hummingbird/bat and passerine pollination, as a model system to study consequences of pollinator shifts on mating systems and population genetic diversity. All selected species were self-compatible, regardless of pollinator type. No signs of pollen limitation were found in the vertebrate pollinated systems. Comparing two bee-pollinated populations at different altitudes, however, showed strong pollen limitation in the high-altitude population. Our population genetic results further support the idea that vertebrate pollinators are better at linking populations over large geographic distances, with higher levels of observed heterozygosity and higher population genetic diversity among populations than in bee pollinated species.