Myrmecochory – Seed dispersing ants!

An Aphaenogaster rudis ant shown in the act of myrmecochory – here dispersing the seed of the forest understory forb, Sanguinaria canadensis (bloodroot).

Myrmecochory is a term that comes from Greek, created from “myrmeco” – of or pertaining to ants, and “chory” – plant dispersal. It is one of approximately seven plant “dispersal syndromes” classified by ecologists, is found in approximately 5% of the angiosperms and occurs in numerous ecosystems around the world.

Showing the extreme relative strength of the ants, this Aphaenogaster rudis is moving a diaspore that must be several times its own weight.

Mutualism is thought to be the basis for this dispersal syndrome. Although this is not necessarily crystal clear, the ants are attracted to the eliasome – the fleshy structure attached to the seed that is a rich source of lipids, amino acids and other nutrients. The ants typically will move the diaspore (eliasome + seed) back to their nests. Dispersal distances vary, but are generally not great – most often 2 meters or less. However, for small forbs this distance is often adequate for moving these propagules outside the range of competition of the parent plant.

Two Aphaenogaster rudis ants attempting to move this Sanguinaria canadensis (bloodroot) diaspore. This was not seen very often and shortly after this image was taken, one ant gave up its pursuit.

Distance dispersal is not the only selective advantage that plants gain from this mutualistic relationship. When the ants have moved the seeds to their nests, they remove the eliasome to feed their young and typically dispose of the seeds in their midden heaps or eject them from the nest. Seeds that are moved to midden heaps or other such locations benefit in multiple ways. First, they are placed in microenvironments that are conducive for germination and early growth. They are protected from heat of fire that could destroy the seeds and benefit from not being accessible to birds and other seed predators. This is referred to as ‘directed dispersal.’ Some studies have shown that the removal of the eliasome may promote germination, similar to the process of seed being removed from their fleshy fruit as it is passed through the gut of a vertebrate.

I rarely had to wait more than 15 minutes before the first Aphaenogaster rudis foraging scout found the pile of diaspores I placed on the ground. Mere minutes after that it was advertised across the colony and other workers showed up to carry the spoils back to their nest.

Their is typically no specialization of particular ants dispersing a particular plant species, with almost any ant species being ready to take advantage of a free meal. The possible exception being that larger diaspores must be dispersed by larger ant species.

Using one of nature’s great predators to disperse your seeds can be risky business. As seen here, the testa (seed coat) of this Sanguinaria canadensis (bloodroot) as well as most myrmecochorous plants is hard and smooth to avoid the bite that ants can deliver.
When a Camponotus pennsylvanicus ant finds a diaspore, the photographer must act quick. They don’t need much time to haul it away!

My hope was to photograph myrmecochory across a variety of species this year. I was fortunate to find success with Sanguinaria canadensis but had no luck in my attempts with Dicentra cucullaria (dutchman’s breeches). I tried hard for trillium species as well but discovered the plants I was waiting for mature fruits for weeks were being harvested most likely by SNR staff. I will be trying for these again in the future and hope to photograph prairie species as well.

A freshly fallen Stylophorum diphyllum (celandine poppy) fruit with diaspores waiting for the ants to disperse them. Note the different testa pattern and eliasome structure compared to Sanguinaria canadensis.

The fruits of Stylophorum diphyllum (celandine poppy), I discovered, had a much smaller window of ripening. I had to check at least every two days or  I would miss the opportunity of a large fruit full of diaspores.

The ubiquitous Aphaenogaster rudis is a key disperser of Stylophorum diphyllum (celandine poppy).
As with many mutualistic relationships, cheaters are known in myrmecochory. Too small to properly move and disperse a diaspore of this size, this Nylanderia faisonensis is seen eating the eliasome on the spot. This was not a very common observation and it is doubtful that this would ultimately hurt the plant species.

See below for my attempts at filming myrmecochory. This was definitely challenging. I had troubles predicting the ants’ behavior, especially while under the bright, continuous lighting needed for high-magnification photography such as this. Something else to try and improve upon next year.

I’d like to thank James Trager for his assistance with ant species identification.

-OZB

One thought on “Myrmecochory – Seed dispersing ants!

  1. I just discovered some scilla in my front and back yards that I did not plant. Information says that ants carry the seeds for about 2 meters. Maybe they used a “bucket brigade” to get a seed to the back yard! Only found one back there.

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