Evolutionary investigations into insect olfaction and host choice using a mosquito model system

A project undertaken at the School of Biological Sciences, University of Queensland, and supervised by Dr Nigel Beebe

Summary

A malaria mosquito host feeding shift was observed in closely related species of the Anopheles punctulatus group in the southwest Pacific islands (Solomon archipelago), where a loss of the ability of these mosquitoes to cue to humans has occurred. As olfaction plays a central role in the host preference this unique situation provides a rich opportunity to investigate the genetic basis of human host cuing in malaria mosquitoes. We have used population genetics to describe this unusual phenomena and then engaged comparative genomic and RNAseq approaches to determine the molecular genetics and evolution of olfaction using members of the An. punctulatus group as the model system.

This research was undertaken as part of a PhD project for Mr Luke Ambrose who has used mosquito collections from Australia, Papua New Guinea and the Solomon Islands to 1) describe this unique mosquito system through population genetics; 2) generate  genomic and transcriptomic data from species/population pairs of closely related mosquito species exhibiting fixed differences in host feeding behaviour; 3) identify genes involved in human seeking olfaction through candidate gene investigations, comparative genomics and transcriptomics; 4) utilise gene knockdown methods to validate candidate genes' involvement in human host seeking.

Outcomes
  1. Multilocus population genetic study of Anopheles hinesorum through New Guinea, Australia and the Western Pacific showed considerable population genetic structure.
  2. Genetic evidence was found for a recent incursion of PNG (human biting) individuals into Western Province of Solomon Islands and these An.hinesorum individuals were found biting humans. This finding is significant as these individuals are now biting humans and carrying malaria in the Western Province of the Solomon and we may be seeing the appearance of another malaria vector species in the region.  
  3. Novel genomes produced from 11 closely related mosquito species and subpopulations for An. hinesorum (both human biting and non-human biting populations), An. irenicus (non-human biting cryptic sister species),  An. farauti (human biting cryptic sister species) that is providing a superb resource for examining the evolution of olfaction.
  4. Olfactory candidate genes have been identified and evolutionary signature studies are still underway.

    


Figure 1. Anopheles farauit feeding.