Parasite-Induced Fruit Mimicry

healthy ant vs nematode red an

ant with red berry gaster

This week I want to talk about another really interesting parasite that infects ants. And yes, it is another nematode. Nematodes are crafty little creatures, because instead of controlling ant behavior, the Myrmeconema neotropicum controls an ant’s appearance.

As you can see from the first picture, the ant Cephalotes atratus on the left looks the way an ant is supposed to look. However, the ant on the right has a red, extended gaster. This is because there are multiple nematodes inside of that part of the ant’s body.

The second picture shows an ant on a plant with some berries. Yes, there is an ant in this picture. But doesn’t it camouflage well with the berries? At first glance you may have mistaken his swollen gaster for a berry. This is exactly the point. Birds see berries and want to go eat them, and when they see this ant, they think it is a berry as well.

Even more interesting is that birds easily pluck the gaster right off of the ant. The gaster of an ant with Myrmeconema neotropicum inside is I think about 15 times easier to pull off, than the gaster of a healthy, non-infected ant. The whole point of this is that the body of the ant is a bit spikey and the ants can bite to try to defend themselves against the bird and therefore if the rest of their body stayed attached to the gaster, the bird would have a more difficult time eating it, especially once it realized it wasn’t a berry. However, this doesn’t happen, and the gaster detaches easily, allowing the bird to better enjoy its snack.

So how do the nematodes make the gaster resemble a berry? What happens is they lie just below the ant’s cuticle (their skin basically) and cause a reddish tint. The actual parasite is yellow, but when seen through the black exoskeleton of the ant it looks reddish in color.

So why is it so important for the bird to eat this ant gaster? Well, because that is the only way the parasite Myrmeconema neotropicum. Ants eat bird poop (containing the adult worms) because it is rich in nitrogen. After they eat it, the adult worms mate within the gaster of the ant pupa. As the ant gets older, the male worm dies while the female worm develops eggs. These eggs are what is seen through the gaster, so then a bird can mistake it for a berry, and the lifecycle continues.

Parasites are so interesting, just the evolution that goes into creating these relationships is fascinating. It is interesting to think that the each specific nematode species has found such a small, specific niche (the infection of only one ant species) to carry out its life. The smart parasites don’t just latch onto a host and drain it of its nutrients so that it eventually dies with the parasite stuck in the host. No, ingenious parasites control, change, use, or manipulate their hosts just long enough that they can reach the next step in their life cycle.

(Also, I know you might be wondering, since I was too when I first learned about this topic: once the gaster is removed does it grow back or can the ant survive? Unfortunately the ant dies. It cannot grow its body parts back once they are removed.)

pic 1: http://ecologia.ib.usp.br/ssmb/doku.php?id=2014:groups:g6:start

pic 2: http://www.redorbit.com/topics/myrmeconema-neotropicum/myrmeconema-neotropicum-images/