April 2, 2015 | David F. Coppedge

Plants Borrow Their Transportation

Seed dispersal in plants is a fascinating study about diverse mechanisms for survival. Here are two methods of hitchhiking on animal transportation.

Emu footwork:  An article on PhysOrg about the second largest bird, the flightless emu, tells how important these animals are for plants. These purpose-driven birds know where to go for their food, and don’t mind taking along some passengers.

GPS technology attached to emus (Dromaius novaehollandiae) has reinforced the role the world’s second largest extant bird plays in dispersing seeds in the environment as well as indicate they have started moving with purpose rather than wandering aimlessly….

Emus are arguably the most important frugivore in the jarrah forest, their generalist diet and gut retention times of up to 100 days mean a large amount and variety of seeds can be deposited in a single scat.

That may sound gross to kids, but the seeds don’t care about riding first class. This cooperative effort benefits both. The bird gets a meal, and the seed gets a ride. It is important for seedlings to land some distance from the parent plant, to prevent inbreeding. The transportation system also provides fertilizer.

Fishgut finwork:  Other seeds prefer the waterways. Another PhysOrg article tells how seeds can travel long distance by taking the fin route. The study shows that plants need to satisfy a balance between having seeds hard enough to avoid digestion, but soft enough to germinate once back on land. It appears the digestive juices of fish (and the emu, above) help prepare the seeds for germination:

Amazing FactsFish can play a role in seed dispersal over large distances. Heavy seeds in particular pass undamaged through the mouths and intestines of fish and may end up being dispersed for miles, both in an upstream and downstream direction. As a consequence, reintroduction of water plants into newly created nature may not be necessary. Freshwater Biology has published a study by ecologists and fish experts from Radboud University and Wageningen University….

The faeces was collected after 28 hours. Did the fish swallow the seeds and then excrete them out again? And if so, were they still capable of germinating? Adult carps were capable of crushing and digesting almost all seeds. Hard seeds (such as pondweed) best survived being eaten by the carp. But the few soft seeds that were excreted undamaged by the fish proved to be the most capable of germinating. The tilapia ate fewer seeds than the carps but more of the seeds they excreted were still viable.

Insect hitchhiking: Fungi are not typically classified as plants; they have spores, not seeds. But like plants, mushrooms are anchored to the soil. Current Biology describes experiments showing that bioluminescent mushrooms turn on their lights to attract insects. The greenish light is specifically targeted to the insects’ visual sensitivity for intensity and wavelength.  As “flies, beetles, ants, wasps and other bugs attracted by the green light” came in for a closer look, they picked up spores from the mushrooms that they would carry off to other locations. “The authors argue that especially in dense forests, where humidity and spore germination are high and there is little wind, nocturnal transport of spores by insects offers some advantage for fungus dispersion.”

Other mechanisms: This is just a small sample of seed dispersal techniques. Air transportation is a large class of mechanisms: we mentioned the helicopter transportation used by pine seeds in the 3/31/15 entry; this works also for maples and other trees that drop their seeds from a height. For low-down plants like dandelions, parachuting is common. Cockleburs hitch rides on cattle (that was the inspiration for Velcro). Coconuts and mangroves can float their seeds across oceans on their own watercraft. Tumbleweeds harness the wind to drive their own sowing machines. Plants like scotchbroom and mistletoe can blast their seeds with miniature cannons. And some common plants, like oats and filaree, equip their seeds with power tools to plant them in the ground.  These and other amazing seed dispersal mechanisms are shown in action in the documentaries Journey of Life and Wonders of God’s Creation by Moody Institute of Science.

Those beautiful films mentioned above are still classics. They make great teaching tools. The films by Moody Institute of Science are still remembered by many, but most are looking dated in this era of HD, Blu-ray and modern video/audio quality. One thing you may not know is that producer Lad Allen and editor Jerry Harned, who made those classics when on staff with Moody, have continued making great documentaries for 18 years with their own production company, Illustra Media. Recently they have been outdoing themselves with fantastic high-def documentaries in the Design of Life series, like Metamorphosis: The Beauty and Design of Butterflies and Flight: The Genius of Birds, which we advertise on this site.  Follow them on Facebook and Twitter (@illustramedia), and buy their films at the Illustra and La Mirada websites. They belong in every nature lover’s library. Their latest masterpiece, Living Waters, about sea life, should be available by summer and is poised to be the best so far.


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