Animals play a big role in keeping our green world colorful. Flowers, flowering trees, vegetables, vines, and more, are pollinated by a variety of animals. Pollination means these animals take pollen from one plant and move it to another plant, so the plants can reproduce.
Usually pollinating animals fall into the arenas of birds, bees, and bats as well as some other insects. Without these animals, many plant species would wither and die, becoming extinct.
This leads us to think plants would be happy for any pollinator to stop by and that they would not be overly focused on any one type of animal, but this is not always true. Blooming plants position their nectar and pollen in specific ways that require certain pollinators. Sometimes the evolution of plants makes them adapt to new pollinator types instead, like from bees to birds. Much of the plant’s reasoning behind such preferences is unclear. If a plant species starts to undergo pressures due to its location, this could cause such drastic shifts in their pollination method.
Recently an international team of researchers from Xi’an Jiaotong-Liverpool University and University of Bonn published a study in the journal Ecology and Evolution that suggests there is more to the decision making of the plant pollination than was previously understood.
This unrelated 3:12-minute video by Nature on PBS is about the tiniest bird on earth, which is known as a Bee Hummingbird. It is a rare bird that is not much larger than a bee, and dwells in the Zapata in Cuba.
Previously it was thought that plants switch pollinator groups from bees to birds because the pollination efficiency of bees is unpredictable or too low, according to Dr. Stefan Abrahamczyk of the Nees Institute for Plant Biodiversity at the University of Bonn in Germany.
Bees get too cold in forests located in tropical mountainous regions that are too humid or have cold temperatures. If this continues over time, and there is a lack of bee pollination efficiency, this might cause a plant to switch to bird pollination. Not all cases of pollination-evolutionary changes can be similarly explained as some can happen in areas with an abundance of bees.
These researchers studied the reproductive systems of three pairs of very closely related plant species, where one species had evolved to hummingbird pollination, the other by bees. A series of pollination studies were done to investigate what advantages the differing pollination methods may give plants and what might initiate such a switch from bee to hummingbird pollination.
They discovered that seeds from hummingbird-pollinated plants had higher germination rates than from plants that were bee-pollinated. This was particularly the case in species where flowers could not be fertilized by pollen from another flower on the same plant, also known as self-pollination.
Hummingbirds travel a longer distance to collect pollen than bees do, and the group suggested that this accounts for the increase in reproductive success. Hummingbirds visit different plants rather than first feeding on all the flowers of a single plant. This increases the odds for cross-pollination between plants. Bees have smaller areas of activity and visit many flowers on the same plant before moving on. Pollen carried on bees is likely to transfer to flowers on the same plant, so this increases the chances of self-pollination. The team found that seeds from cross-pollinated fertilization had higher germination rates than those from self-pollination in both bee and bird-pollinated plants. This supports the explanation.
Dr. Abrahamczyk says these results support the conclusion that hummingbird pollination evolved in bee-pollinated species that are quite dependent on cross-pollination and cannot self-pollinate.
The study’s findings also indicate hummingbird pollination offers less waste of pollen than bee pollen and more efficient fertilization. All hummingbird-collected pollen fertilizes plants. Bees roll some pollen into pellets to place in the pollen baskets on their legs and groom their bodies during flight. Bees feed the pollen to their larvae. Plants realize there is an increased chance of reproductive success with hummingbird pollination, so it could be another reason for a plant’s change to hummingbird pollination.
Dr Abrahamczyk says that these newly gained insights can also be applied to the evolution of other pollination systems, like moth or bat pollination.
This study offers a deeper insight into plant-pollinator interactions, but further tests are needed to confirm this explanation of the pollination-system evolution.
If you would like to read the study, it is called, ‘Influence of plant reproductive systems on the evolution of hummingbird pollination,’ and can be found here.
The intelligence of flowers that this indicates, as well as their ability to communicate with one another, is simply stunning. What an exciting area of research. We will bring more on this theme as we come across it.