Characterize the types of symbioses involved in the ant-wasp-aphid-buchnera-secondary symbiont system. Which pairs of species interactions do you think represent symbioses? Which pairs of interactions do you think are too weak or distant to be considered symbioses?

Question

What will be an ideal response?

Answer 1

In the early to mid- 1990s, Angela Douglas discovered that pea plant aphids could not live without a certain species of bacteria in their gut. The pea plant aphid obtains most of its essential amino acids not from it's food source (phloem), but from an endosymbiotic bacterium (Buchnera) that synthesizes the amino acids directly.

Aphids typically feed on phloem, which is the sugary water that plants produce as a result of photosynthesis. They exude a small drop of liquid from the end of their back of their abdomen. Amino acids constitute only about 1% of phloem, so you have to suck a lot of sap to get what you need. Aphids don't defend themselves very well because they are stuck sucking sap most of the time. Ants actually serve as bodyguards and harvest the drops for sugar themselves.

To get a more completely balanced diet, however, aphids associate with a specialized endosymbiotic bacteria called Buchnera. These bacteria are stored in specialized cell structures called bacteriocytes in their guts. In the bacteriocytes, aphids supply sugars and other compounds to the bacteria, which in turn produce amino acids to supplement the nitrogen-poor plant sap diet of the aphid.

Buchnera makes up about 90% of the microbial cells inside of aphids, but there are other microbes present. The role of these secondary symbionts was not particularly well understood until relatively recently. Wasps parasitize the aphids by laying their eggs inside of them and when the larvae hatch they start to eat the aphid and kill it. The presence of other the secondary symbiont bacteria can significantly reduce aphid parasitism by the wasp, primarily by reducing the health of wasp larvae inside the aphid.

Direct symbiosis between organisms in this system could include:
1) Ant-aphid synergism
2) Aphid-Buchnera mutualism
3) Aphid-Secondary symbiont mutualism
4) Aphid-Wasp parasitism

Indirect symbiosis between organisms in this system could include:
1) Ant-Wasp amenalism
2) Ant-Buchnera synergism
3) Ant-Secondary symbiont mutualism
4) Buchnera-Wasp amenalism
5) Secondary symbiont-Wasp amenalism