Seeds glue themselves to the ground to escape seed predation

Vincent S. Pan, Marshall McMunn, Richard Karban, Jake Goidell, Marjorie G. Weber, Eric F. LoPresti

A harvester ant (Pogonomyrmex subdentatus) attempting to dislodge a mucilage anchored seed (Gilia leptantha). Photo taken by Eric LoPresti.
A harvester ant (Pogonomyrmex subdentatus) attempting to dislodge a mucilage anchored seed (Gilia leptantha). Photo taken by Eric LoPresti.

The seeds or fruits of thousands of plant species produce a sticky substance called “seed mucilage” when wetted. You may have seen seed mucilage before if you have encountered chia (Salvia hispanica), flax (Linum usitatissimum), or psyllium powder (Plantago ovata). Even though seed mucilage is often treated as a single trait, there are in reality spectacular chemical, physical, and evolutionary diversities among different species.

In this study, we tested the hypothesis that the seed mucilage of 53 distantly related species glues seeds to the ground, thereby preventing predation by seed eating ants. We presented seeds with or without their mucilage released to harvester ants and found that ants overwhelmingly took the seeds without mucilage. Seeds that released more mucilage stuck more strongly to the ground, which made it more difficult for the ants to pick up the seeds. We thus conclude that one widespread shared function of seed mucilage is to defend seeds against predation.

              To better understand the ecological and evolutionary context of seed stickiness, we combined data on 432 species from previously published studies and looked for broad trends. We found that closely related species have seeds that are more similar in stickiness. Seeds are stickier if they originate from hotter places with more sunlight or places closer to 30° latitude. Seeds are also stickier if the seed is denser or if the plant is shorter lived. Surprisingly, we struggled to find an association between seed stickiness and habitat dryness. We proposed some hypotheses about these newfound suggestive associations and advocate for more mechanistic investigations into these exciting possibilities.

Read the research in full here

One thought on “Seeds glue themselves to the ground to escape seed predation

  1. Odd – around 3000 species of plants have seeds with elaiosomes to attract ants as dispersers (the ants eat the elaisosome, but disgard the seed). By the size ratio of seed to ant, the ant could surely consume the seed in situ? What is the trade off? Do the ants never consume seeds they can not move and what happens to seeds where the attachment fails? Do they get moved by ants, presumably back to the nest? Do they ever germinate?

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