worms plant ragweed seeds

[eub]

http://www.sciencenews.org/view/generic/id/33699/title/Ecosystem_engineers

Led by weed ecologist Emilie Regnier of Ohio State University in Columbus, researchers conducted field experiments to determine how exotic European night crawlers, Lumbricus terrestris, affected the survival of the seeds of Ambrosia trifida, giant ragweed.

In addition to its powers as an allergen, ragweed is a major weed of soybean fields and cornfields in the Midwest, Regnier says. This fact has puzzled scientists because ragweed seeds are usually quickly eaten by birds, rodents and beetles.

Worms collected and buried more than 90 percent of ragweed seeds from the surface of the soil around their burrows, the team reports.

“The burrow is an environment that the worm is actively maintaining — that’s its universe,” comments soil and ecosystem ecologist Patrick Bohlen, director of the MacArthur Agro-ecology Research Center in Lake Placid, Fla. “Maybe it’s sweeping its front porch. We don’t really know. There isn’t a lot of evidence that they are eating the seeds, but clearly it’s creating an architecture.”

Do they plant other seeds too? We want to know.

Maybe worms like ragweed seeds as gizzard stones.

I was hoping this could be a deep-dyed plot between Lumbrici to spread the seeds, and trifid Ambrosia to... strangle competitor worms with its roots, or something. But ragweed is exotic to Europe.

ETA: sock puppets! mouth suction!

Comments

[eub.livejournal.com]

And even the details in this SN article seem to be in this 2006 story. I sometimes wish SN would include a reference to the publication they're reporting on.
http://www.agriculture.purdue.edu/AgAnswers/story.asp?storyID=4321

Darwin observed everything first, didn't he.

In 1881, Charles Darwin, in his book “The Formation of Vegetable Mould, Through the Action of Worms with Observations on Their Habits,” reported earthworms collecting glass beads and tile fragments.

I assumed that worms were ingesting the seeds to transport them, because they don't have opposable thumbs, but they do! And they... suck onto smooth objects with their mouth and drag them that way?

“Giant ragweed seeds have a lot of variation in their shape and size, and they have ridges along the sides and a 'beak' at the tip of the seed, which might make it easier for the earthworm to grip it,” said Regnier, equating how an earthworm grabs items to that of how something is grabbed with a sock puppet. “Things that are more round and smooth, like soybeans, may be more difficult for the earthworm to grip, although earthworms can also apply suction to move smooth objects.”

[3smallishmagi.livejournal.com]

Hmm. The article wonders why earthworms would do this, but perhaps it's the ragweed that is acting here. The seeds apparently vary a lot.

This:
http://www.cdfa.ca.gov/PHPPS/ipc/weedinfo/ambrosia-trifida.htm
is a pretty purposeful looking seed.
(http://www.oldthingsforgotten.com/seeds/ambrosia_trifida.jpg)
http://www.oardc.ohio-state.edu/seedid/single.asp?strId=16

The earthworm stumbles across the cunningly designed seed and gets it stuck in its beak. It then runs away trying to shake it off.

Another speculation is that it is the seed size variation that is the evolved strength of the ragweed. It has of course been around for millions of years, and habitats change quite a lot (having your descendants grow up downstream is the same sort of thing) Each time it has to figure out a new best way to get its seeds dispersed.