Possible ecological and evolutionary effects of protocooperation between ants and aphids.

Abstract

The association between ants (Hymenoptera: Formicidae) and aphid colonies (Homoptera: Aphididae) has been studied since before the turn of the century. In exchange for honeydew secreted by the aphids, ants purportedly provide them with improved hygene, help contain overcrowding, ensure aphids a nutritious food source, and protect aphids from predation. In this study, we used the predators Hippodamia convergens (ladybird beetles) and Chrysoperia carnea (lacewing larvae) to test the protection of aphid colonies by ants. The study was conducted using leaves of 24 Populus Grandidentata saplings at the University of Michigan Biological Station, in northern lower Michigan. The predators were placed on leaves with aphid colonies in the presence of ants and in the absence of ants. We found that in the presence of ants, predation occured in only 1.7% of the 60 trials and the predators were removed or killed within five minutes 86.7% of the time. In the absence of ants, predation occured in 55.0% of the trials, 33 times out of 60. Our results show that ants do protect aphid colonies from predation by H. convergens and C. carnea. The benefits recieved by ants and aphids in association with each other allow us to say that there is a protocooperation between the organisms. This protocooperation may be a very powerful force in the ecology and evolution of ants and aphids. The association between ants and aphids may be a good example of protocooperation which can help us theorize about how protocooperation may affect the ecology and evolution of organisms.