Spring Wildflowers and Ants: Part 1 of The Evolutionary Best Buds Series
Each spring ephemeral wildflowers burst through the forest floor to take advantage of plentiful sunlight and an abundance of pollinators but, there is one type of organism that is particularly excited to see them (besides us naturalists), the Ants.
The Southern Appalachian Mountains support a tremendous amount of plant diversity due to its large amounts of rainfall and sunlight. This leads to a lot of plant competition, and whenever an ecosystem has a lot of competition it will also have a wide variety of adaptations and symbiotic relationships that help one gain any survival advantage possible. The Ant and most of the spring wildflowers have developed a tight knit cooperation that allows both to thrive during a period where there aren’t many organisms brave enough to risk the uncertain weather of spring in the mountains.
Many wildflowers of early spring are pollinated by native and invasive bees but two types of plants, Wild Ginger (Asarum canadense) and Little Brown Jugs (Hexastylis sp.), have evolved to give the ant an important role. They have flowers that are pollinated by small flies and crawling insects, such as the ant, that emerge from the ground after winter (http://www.fs.fed.us). They do this by growing flowers that lay on the ground which make them hard to see unless you’re really looking for them. They are a beautiful maroon color that is said to attract the insects by being the same color of what the insects are really looking for, a rotting carcass. Studies show that Wild Ginger, after a period of time passes without an insect visitor to help get it’s pollination on, will change the direction of their stamen and stigmas in order to self-pollinate (Lu, 1982). The plant must figure that if it can’t successfully “cross-pollinate” then it will just have to take matters into its own hands.
Ants play a major role in seed distribution for many of our spring wildflowers, and they do so in a way that let’s everyone win. Many of the Violets’ seeds are spread by Ants as well as Dwarf Iris’s, and Bloodroot. Plants that have developed a relationship with Ants in Appalachia (and elsewhere) usually have a hard waxy seed that has a nice little white “handle” on the outside of it. This little white protrusion, called the Elaiosome, is the key to this mutualistic relationship because it is full of yummy nutrients that the Ant wants. So, the ant carries the seed back to its nest where it removes the Elaiosome and feeds it to the developing larvae. So, what does the plant get out of it you ask? Well, it gets a few different things that increase the chances of that seed surviving. First, it gets its seed taken away so it doesn’t have to compete against it for sunlight once it is grown. Secondly, since the seed is taken away from the plant, the likelihood of a seed predator coming and eating the seed gets reduced dramatically. Thirdly, the seed is the taken to the Ant’s garbage pile which is usually full of discarded materials that will give the plant vital nutrients in its early stages of growth (Beattie, 1985). So everyone wins, unless you’re the animal who is cursing the little ants for taking off all of the yummy seeds.
Beattie, A.J. 1985. The evolutionary ecology of ant-plant mutualism. Cambridge University Press. Cambridge, England
Lu KL. 1982. Pollination biology of Asarum caudatum (Aristolochiaceae) in northern California. Systematic Botany 7(2):150-157