The role of pollinators in the evolution of flowers with various sexual forms
Scientists have shown that Darwin’s theories of precise pollination in heterostylous plants hold true on a large scale
Researchers Violeta Simón, Marcial Escudero and Juan Arroyo, from the Department of Botany at the Faculty of Biology of the University of Seville, led a study in which, in collaboration with researchers from four other countries, they demonstrate Darwin’s hypothesis of precise pollination across all angiosperms (flowering plants).
In heterostylous species there are two (sometimes three) types of flowers, called morphs, which differ according to the location of their sexual organs. The L-morph has the stigma (female sex organs) higher and the anthers (male sex organs) below. And in the S-morph they are the other way around. Darwin proposed that this system evolved to promote cross-pollination (between different individuals, to increase the vigour of their progeny) through a mechanism of precise pollination between the male and female sex organs of each morph, on different parts of the pollinator’s body.
This hypothesis of precise pollination hinges on the presence of floral traits and pollinators that fit together like a jigsaw puzzle, so that pollen is accurately deposited and transferred.
“We conducted a comprehensive review of the presence of heterostyly in all angiosperm genera and found many more cases than had been reported in recent literature reviews on the subject. We then collected more than 10,000 data about floral morphology and pollinators across many heterostylous and non-heterostylous species, and placed these data into a mega-phylogeny of all angiosperms to find whether the evolution of heterostyly is associated with floral traits and pollinators that promote precise pollination,” explains researcher Violeta Simón.
By looking at the correlations between heterostyly, floral traits and pollinators, the researchers found that heterostyly does indeed evolve in flower lineages with a narrow floral tube and long proboscis pollinators such as butterflies and moths. These pieces fit together to allow pollen to be transferred precisely from one morph to another, as Darwin predicted.
“Heterostyly has been used as a model for studies of floral evolution since Darwin’s time, but such an ambitious study on a macroevolutionary scale has never before been undertaken. We believe it will be a seminal work for many researchers in this field,” says the researcher Simón. It is worth stressing that this research group has been studying this plant reproductive mechanism for almost 30 years, and is a leader in the role of ecology in its evolution.
This project received funding from the European Union’s Horizon 2020 research and innovation programme under the agreement 897890, grant PID2021-122715NB-I00 DiversiChrom funded by MCIN/AEI/ and by “ERDF A way of making Europe”.
JOURNAL
Nature Communications
ARTICLE TITLE
Convergent evolutionary patterns of heterostyly across angiosperms support the pollination-precision hypothesis
Scientists gain insight into a buzzing spring pollinator that plays a significant role in the almond industry
US DEPARTMENT OF AGRICULTURE - AGRICULTURAL RESEARCH SERVICE
April 2, 2024
The USDA’s Agricultural Research Service (ARS), in collaboration with the Ecological Forestry Applications Research Centre in Spain and North Dakota State University, conducted a comparison of the physiological and molecular processes involved in the summer and winter dormancy of Osmia lignaria, also known as blue orchard bee or orchard mason bee.
This analysis of gene expression is believed to be the first to compare the dormancy periods of this species in their natural habitat, and more importantly, it led to sequencing the first draft genome of this important pollinator for the almond industry.
According to the U.S. Forest Service, North America has 140 species of Osmia. Osmia lignaria, a solitary bee, follows a one-year lifecycle that includes two periods of dormancy. During summer, the bee develops to the prepupal stage (the stage of larva after its final molt), pauses, then finishes to developing to the adult stage before winter. Adult bees slow their metabolic activity while overwintering [second dormancy]. When spring arrives, adult bees emerge from dormancy and become highly active in pollination. Although this species does not produce honey, it is very effective in pollinating almond trees due to cross-pollination among different varieties, which leads to higher crop yields.
Osmia ribifloris is one of several relatives of the blue orchard bee (Osmia lignaria). These bees are effective pollinators for almond trees due to the way they cross-pollinate among different varieties, leading to higher crop yields. (Photo by Photo by Jack Dykinga)
“This species inhabits a wide latitudinal range in North America, with populations in the north having different developmental rates and lengths of dormancy periods than those in southern populations,” said Alex Torson, a computational biologist with ARS’ Insect Genetics and Biochemistry Research in Fargo, North Dakota.
“In the future, we can use the genome presented in this study to start comparing the genomes of individuals from these different geographic populations. If these differences in development and dormancy can be traced to their genetics, then we could develop managed populations from different geographic locations, and time the characteristics of those populations with peak floral blooms for different types of crops.”
By aligning their emergence with the timing of crops, it would allow for better management and pollination, as this bee species emerges in the spring and is a significant pollinator of almond trees due to how it pollinates.
Understanding how this lifecycle occurs has become increasingly important due to changes in environmental conditions. A better understanding of the evolutionary relationships among populations of this species will be critical for developing managed populations we can use for pollination services.
The study is available in Insect Biochemistry and Molecular Biology.
The Agricultural Research Service is the U.S. Department of Agriculture's chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in U.S. agricultural research results in $20 of economic impact.
JOURNAL
Insect Biochemistry and Molecular Biology
ARTICLE TITLE
Metabolic and transcriptomic characterization of summer and winter dormancy in the solitary bee, Osmia lignaria
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