Pollination is the transfer of pollen from the male to female plant reproductive organs which leads to germination and fertilization of seeds. The resulting fruit helps to protect the seeds and helps with their dispersal. Through evolution plants have adapted to ensure successful reproduction by pollinators and pollinators have adapted to use flowers as a resource for growth and reproduction. This week’s blog discusses wild blueberry pollination and flower ecology, and why pollination can be so difficult.
Wild Blueberry Flower Ecology
Plants have flowers for sexual reproduction, to produce new plants with genetic material from both parents. In the wild blueberry industry, the focus on flowers is fruit production. Wild blueberry flowers contain both male and female reproductive organs, stamens and pistils respectively. The female organs contain a stigma for receiving pollen, at the end of a style, with ovaries at the base. The male organs contain pollen on an anther, at the end of a filament. The flower parts like petals and sepals help to protect the reproductive tissues throughout pollination, germination, and fertilization. Since plants are immobile, they need wind, water, or animals to transfer pollen. Wild blueberries require animal pollination due to their flower structure [3]. Therefore, there is a mutual relationship between flowers and pollinators, which is reproductive success of the plant in exchange for nectar and pollen for the animal.
About 90% of flowering plants use animal pollinators for reproduction. There are more than 130,000 species of animal pollinators, containing more than 25,000 species of bees [5]. Wild blueberry flower pollination is generalized, meaning most flowers receive many kinds of pollinators, and the flowers do not specialize in the needs of the best pollinator [5]. This benefits the plant because pollinator populations and biodiversity can vary in different areas, visiting times may be different between pollinators, and weather conditions may not be ideal during bloom for certain pollinators. So, attracting many pollinators will allow for more effective pollination. From the pollinator’s perspective, it does not want to be a good pollinator; it just wants the resources the flower provides. Therefore, only about 1% of all pollen successfully reaches the stigma [5].
Plants have many ways of attracting pollinators to help with reproduction. These include, but are not limited to, individual flower or whole plant characteristics, attractants, and rewards. Individual flowers can display colors (including ultraviolet colors which humans cannot see), different shapes, and timing of flowers opening. Whole plants can vary in density, number, height and pattern of flowers. Attractants include visual and olfactory cues, and rewards include nectar and pollen availability. It is in the plants’ best interests to support pollinators or improve pollinator efficiency, such as ensuring the pollinator visits the necessary flowers. The plant can do this by changing color, odor, or shape after the flower is successfully pollinated, to prevent wasted effort of the pollinators [5].
Attractants are an efficient way to lure pollinators, but they can also attract unwanted visitors. If there is not an effective transfer of pollen from the anther to the stigma, then the pollinator is known as an illegitimate visitor or cheater. Therefore, measuring pollination success should not be done by only observing the number of animal visitors to flowers. There are more precise ways of identifying pollinator success, such as single visit deposition on virgin flowers [2]. ATTTA has also done many studies where fruit set and the number of viable seeds is counted after pollination to determine pollination success [1].
Plants and animals have a competing interest, which has led to adaptation and counteradaptation through evolution. Both parties want a larger share of resources for growth and reproduction. An ideal pollinator, from the plant’s perspective, is one that is cheap to feed, stops briefly, moves rapidly to another plant of the same species, and is faithful to that species. The ideal flower, from the pollinator’s perspective, is one that provides lots of nectar or pollen, which requires spending less energy [5]. An example of this in wild blueberries is the adaptation of the poricidal anthers [3], which allows slow pollen release and prevents loss of pollen due to eating. The bumblebee has adapted to this with buzz pollination [4], which is sonication to help shake large amounts of pollen from poricidal anthers. Plants use resources to provide attractants and rewards, and if the plant reduces these too much then the pollinator will likely not be interested in visiting. Plants must compete with other plant species for the best pollinators to ensure successful reproduction and the plant also must offset costs with cheaters or flower eaters that are inadvertently attracted.
Pollination ecology is important because it provides insights into evolution, animal learning, forage behavior, biological processes and patterns, and evolution by natural selection [5]. The wild blueberry industry has a higher demand than supply for pollinators, so understanding flower ecology and pollinator behavior can help provide efficiencies around wild blueberry pollination.
Written
by John MacDonald, ATTTA Seasonal Apiculturist
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connect with ATTTA specialists or learn more about our program, you can:
visit our website at https://www.perennia.ca/portfolio-items/honey-bees/
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References:
[1] Bennett, A. and A. Byers. 2023. Best management practices
guide for honey bee pollination of wild blueberries in Atlantic Canada.
Atlantic Tech Transfer Team for Apiculture.
[2] King, C., Ballantyne, G. and Willmer, P.G. 2013.Why
flower visitation is a poor proxy for pollination: measuring single-visit
pollen deposition, with implications for pollination networks and conservation.
Methods in Ecology and Evolution 2013, 4: 811–818.
[3] Orr, J., Byers, A., Morandin, L.A., Medeiros, S.J. and
K. Law. 2023. Practices to protect pollinators from pesticides: wild blueberry.
Pollinator Partnership Canada and Atlantic Tech Transfer Team for Apiculture.
[4] Vallejo-Marin,
M. 2018. Buzz pollination: studying bee vibrations on flowers. New Phytologist
2019, 224: 1068-1074.
[5] Willmer, P. 2011. Pollination and flower ecology. Chapter
1: why pollination is interesting. Princeton University Press.