Elevated atmospheric carbon dioxide concentrations promote ant tending of aphids

1. Animal mutualisms, which involve beneficial interactions between individuals of different species, are common in nature. Insect-insect mutualism, for example, is widely regarded as a keystone ecological interaction. Some mutualisms are anticipated to be modified by climate change, but the focus has largely been on plant-microbe and plant-animal mutualisms rather than those between animals. 2. Ant-aphid mutualisms, whereby ants tend aphids to harvest their honeydew excretions and, in return, provide protection for the aphids are widespread. The mutualism is heavily influenced by the quality and quantity of honeydew produced by aphids, which is directly affected by host plant quality. Since predicted increases in concentrations of atmospheric carbon dioxide (eCO2) are widely reported to affect plant nutritional chemistry, this may also alter honeydew quality and hence the nature of ant-aphid mutualisms. 3. Using glasshouse chambers and field-based open top chambers we determined the ef...