Case Study – a successful grant applicant

Behavioural reproductive ­isolation in Drosophila montana

Paris Veltsos . School of Biology, University of St Andrews

How many genes need to change in a fly before it becomes a new species?  The quest for discovering such ‘speciation genes’ has been based on either top-down (start with lab mutants in candidate genes) or bottom-up (start with population analyses leading to genomic regions) approaches.  We aim to combine the two by conducting a QTL (quantitative trait locus) study based on a pedigree of wild-caught flies.  QTL studies are, at a basic level, correlations between phenotypes and genotypes.  Advances in sequencing technology allow for the genotypes to include both candidate genes, and neutral markers, hence the marriage of the bottom-up and top-down approaches.  When asking evolutionarily relevant questions, it is very important for the genotypes studied to represent natural genetic variation. For example, while mutants in candidate genes display relevant phenotypes, they are usually identified in the lab and might never have survived in the wild. Collection of flies from the wild is therefore an essential part of the project.

Our phenotypes of choice are potentially essential for mating: they characterise the systems of courtship song and cuticular hydrocarbons – fly pheromones. The male-female interactions during courtship can be thought of as sender-receiver systems, albeit in a language we are not used to: song, smell and taste.  Compatibility between the actual and expected message, determines the chances of mating. Given enough time, the courtship systems can evolve to different directions in different populations. Populations evolving independently can end up ‘tuned out’ of each other so that, if they were to meet, the individuals from one would avoid mating individuals from the other. This seems to be the case for courtship song frequency in the fly Drosophila montana, where the female preference has evolved to different directions in US and Finish populations1.

The study will increase our understanding of the genetic basis of variation in important traits to reproductive isolation, and hence, potentially, the first steps in speciation. The availability of multiple pedigrees will allow to scratch the surface on tantalising questions. For example is the same genetic architecture responsible for trait variation in different populations? Is evolution predictable i.e. is the same result reached independently in different populations through the same genetic pathways?  We hope to successfully establish pedigrees from Colorado and Kuusamo, and compare them to the one established from Vancouver last year. The field grant provided by The Genetics Society, has funded a collection at a field station near Kuusamo, Finland. This is a location from which the group of Prof Anneli Hoikkala, with which we collaborate, have been consistently sampling with success in the past. (This year they collected from Colorado, see http://mountainflyers.wordpress.com/).

The trip from Edinburgh was quite adventurous, requiring a 5 hour drive preceded by 3 flights, before reaching the field station. But it was definitely worth it, as the remoteness of the location contributes to its beauty and calmness. The first 3 days were very disappointing, as the temperature was below 5oC and there were brief instances of snowing – conditions far from ideal for fly collection.  We took the opportunity to visit the Kiutakongas rapids, the most impressive in the country, at least according to the local national park sign.  Eventually the weather did improve and by the end of the 10 day trip we had about 300 flies, which should be sufficient for obtaining the offspring of 40 D. montana females – our aim for the founders of the pedigree.  We will only know how many D. montana were caught after they are interviewed: 3 species coexist and they are indistinguishable except for when they are allowed to sing.  I would like to thank The Genetics Society for making the trip possible.