Pollen analogues are transported across greater distances in bee-pollinated than in hummingbird-pollinated species of Justicia (Acanthaceae)

Several hummingbird-pollinated plant lineages have been demonstrated to show increased rates of diversification compared to related insect-pollinated lineages. It has been argued that this pattern is produced by a higher degree of specialization on part of both hummingbirds and plants. We here test an alternative hypothesis: The often highly territorial hummingbirds may on average carry pollen over shorter distances than other pollinators and drive diversification by reducing gene flow distances. We present experimental data from pollen analogue tracking showing shorter dispersal distances in hummingbird- than in bee-pollinated species among ten neotropical species of Justicia (Acanthaceae).