Active pollination drives selection for reduced pollen-ovule ratios.

Area of Science:

• Evolutionary Biology
• Plant Sciences
• Ecology

Background:

• Pollen-ovule ratio (POR) is theorized to reflect pollination efficiency.
• Active pollination mutualisms involve pollinators purposefully transferring pollen, suggesting high efficiency.
• Few studies have directly linked POR to pollen transfer efficiency.

Purpose of the Study:

• To investigate if increased pollen transfer efficiency in active pollination systems leads to reduced pollen-ovule ratios.
• To test the hypothesis using evolutionary transitions from passive to active pollination.

Main Methods:

• Collected pollen and ovule data from plant species across four active pollination brood mutualisms.
• Employed phylogenetically controlled tests and sister-group comparisons.
• Examined the impact of shifts from passive to active pollination on POR.

Main Results:

• Actively pollinated plants exhibited significantly lower pollen-ovule ratios compared to closely related passively pollinated taxa.
• Phylogenetically corrected analyses revealed an average 76% reduction in POR for actively pollinated species.
• Demonstrated a consistent pattern across multiple independent evolutionary transitions.

Conclusions:

• The findings support the utility of pollen-ovule ratios as indicators of pollination efficiency.
• Pollen transfer efficiency plays a central role in the evolutionary dynamics of pollen-ovule ratios.
• Active pollination mutualisms represent a key evolutionary pathway towards reduced POR and enhanced pollination effectiveness.