Chemosensory genes and the evolution of aphid host races

Lead Research Organisation: University of York
Department Name: Biology

Abstract

The process of speciation involves the progressive evolution of reproductive isolation between divergent populations. When this process happens in the face of gene flow, differentiation is expected to be variable across the genome reflecting the direct operation of natural selection and the barrier created for regions surrounding selected loci. Population genomics and QTL mapping approaches have recently contributed significantly to detecting regions under selection and associated islands of differentiation but further progress is difficult in many systems. We argue that a candidate gene approach can significantly advance this field. We propose to study sequence and expression divergence for the entire known repertoire of chemosensory genes in host races of the pea aphid. This study system is unique in having multiple races at different levels of divergence, excellent background information and a sequenced genome. This allows us to apply the latest approaches (Nimblegen capture arrays, 454 sequencing and Illumina Digitial Gene Expression) to this major problem in evolutionary genetics.
 
Description Our aim was to test the hypothesis that divergent selection has operated on a small subset of chemosensory genes during the formation of host races of pea aphid. We predicted that this selection would have generated either (1) patterns of sequence divergence that are atypical with respect to background divergence in randomly selected control loci, and the majority of chemosensory loci, or (2) differences in gene expression that are similarly atypical, or both.

We have used a recently-published approach to check for copy-number variation and have found evidence for widespread duplication and loss which is non-randomly associated with gene families, being more common than expected in the odorant receptor genes. In some cases, copy number variation is strongly associated with race suggesting that it may play a role in host-associated differentiation.
We have published results of a pilot capture experiment and we have also published the exciting and novel copy-number variation results.
We have identified a small subset of chemosensory genes implicated in divergence between pea aphid host races through their role in host recognition. Surprisingly low gene expression responses to host-switching but large expression differences among races have been observed. These manuscripts are currently under review.
Together, these observations take us closer to understanding the evolutionary steps underlying host race formation.
Exploitation Route The main beneficiaries are the academic community through a deeper understanding of speciation genomics.

However, we have communicated some of our findings to the agricultural sector to raise awareness of potential applications in agriculture in the future.

We are taking forward these observations in our current grant by testing for selection on candidate genes and for association between these genes and the aphids' acceptance of hosts as a function of their metabolite composition. In general, this will help to understand how aphids make feeding decisions and may eventually help in development of methods for aphid control.
Sectors Agriculture, Food and Drink
 
Description The PI at Sheffield (Butlin) and Project Partner Zhou attended the CropWorld2012 conference in London and distributed a flier about the potential of our results to underpin the design of new aphid control strategies.
 
Description Speciaphid 
Organisation French National Institute of Agricultural Research
Department INRA Rennes Centre
Country France 
Sector Public 
PI Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Collaborator Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Impact The collaboration involves researchers specialising in ecology, evolutionary biology, agricultural sciences, genomics and bioinformatics.
Start Year 2012
 
Description Speciaphid 
Organisation University of Montpellier
Department Institute of Evolutionary Sciences (ISEM)
Country France 
Sector Academic/University 
PI Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Collaborator Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Impact The collaboration involves researchers specialising in ecology, evolutionary biology, agricultural sciences, genomics and bioinformatics.
Start Year 2012
 
Description Speciaphid 
Organisation University of Oxford
Department Department of Zoology
Country United Kingdom 
Sector Academic/University 
PI Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Collaborator Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Impact The collaboration involves researchers specialising in ecology, evolutionary biology, agricultural sciences, genomics and bioinformatics.
Start Year 2012
 
Description Speciaphid 
Organisation University of Sheffield
Country United Kingdom 
Sector Academic/University 
PI Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Collaborator Contribution Our work on speciation in aphids and on the role of bacterial symbionts in aphids is done under the speciaphid agreement, an agreement between French and British researchers to coordinate their research efforts on this system, collaborate and share material. We have exchanged samples, data as well as meeting on a regular basis.
Impact The collaboration involves researchers specialising in ecology, evolutionary biology, agricultural sciences, genomics and bioinformatics.
Start Year 2012
 
Description School Visit (York) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact 60 primary school children attended this session, which sparked interest in entomology, aphids and ecology more generally
Year(s) Of Engagement Activity 2017