An ancient push-pull pollination mechanism in cycads

June 12, 2020
Shayla Salzman in field with zamia

Pollination is often a mutual relationship between flowering plants and insects. Understaning how these plants entice diverse insects to pollinate has major implications across evolutionary, ecological, organismal and conservation biology. One mechanism that can provide a window into ancient insect pollination, before the rise of flowering plants, are Cycads. Cycads are primary seed-producing plants and represent one of the oldest lineages of seed plants. These plants rely on insect pollination, yet do not display the colorful visuals that signals to pollinators, which is common to flowering plants and a major mechanism in pollination biology. 

In a study in Science led by Shayla Salzman ('19, N. Pierce & Hopkins), Postdoc James Crall ('17, N. Pierce), and Professors Naomi Pierce and Robin Hopkins teamed with Damon Crook (USDA) to uncover the mechanism by which these ancient endangered plants entice pollinators to service their brood site (deceptive breeding sites for insects that are housed in the pollen cone).  Using a combination of chemical ecology and insect behavior, researchers found that a push-pull mechanism of alternating attraction and repulsion, coinciding with heat producing plants, acts to move pollinators between pollen and the female cones of the plant, which when fertilized by pollen, become seeds.

The study's fossil evidence and phylogenetic analysis show that this push-pull mechanism is likely ancestral in this group of plants and represents one of the earliest insect pollination mechanisms, well before the rise of flowering plants.



Image: Shayla in the field with zamia. Courtesy of Rory Maher