Candidate genes for host association in aphids

The origin of new biological species depends on the evolution of characters that prevent them from mating and producing successful offspring. This evolutionary process may start with adaptation to new environments but this rarely creates a complete reproductive barrier. If some interbreeding occurs, then genes which are not directly involved in adaptation to different habitats can still be shared. We still have little understanding of how evolution proceeds from this point to the point of complete prevention of interbreeding.
In this project, we propose to study the pea aphid because its genome has been sequenced and it is known to feed on several different host plant, which represent distinct environments. We know that aphids tend to reproduce with others that use the same plant. This tendency is stronger in some cases than others so we have several points on the progression towards new species that we can compare.
Aphids use chemical cues to choose the plant on which they feed and we now know the types of genes underlying recognition of these cues. We have already found some of these genes that are likely to be involved in the differences in behaviour between aphids that use different plants. In this new project we want to find out how these genes are influenced by natural selection and how they affect the sharing of other genes between host races of aphids. We also want to find out which chemicals in the plants are used in the recognition process.
This will help us to understand the origin of species and it may also help in control of aphids that are pests of crops. Understanding how aphids choose the plants they want to feed on can provide new tools to prevent aphid damage.

Who will benefit from this research?

In addition to academic beneficiaries, we identify two interested groups:

1. Agriculturalists and horticulturists - many aphid species are agricultural or horticultural pests. Most are host specialists. Understanding how aphids discriminate host plants from non-host plants holds great interest in these sectors.
2. The public - evolution is of great public interest, and is often a controversial topic. The origin of species is of particular interest, partly because of the title of Darwin's book and partly because some groups find modification within species easier to accept than the origin of new species. Speciation is a slow process and therefore difficult to demonstrate in a satisfactory way. Cases like the pea aphid, where mutliple different stages in the process of divergence are available, are good vehicles for education about speciation.

How will they benefit from the research?

1. We do not expect directly exploitable results from this project but it may indicate new strategies for aphid control. We will ensure that relevant results are communicated to potential beneficiaries through appropriate publications, attendance at meetings and direct contacts with companies.
2. Public understanding of evolution contributes to the quality of life, particularly in modern society where evolution is relevant to many societal problems ranging from antibiotic resistance to management of fish stocks. We will communicate our results to the public through appropriate publications and other means of dissemination.