Myrmecochory – Seed dispersing ants!

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.

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.

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.

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.

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.

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.

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