Sequence Evolution & Population Genetics in Pine Processionary Moth Populations
Pine Processionary moth (PPM) is an important pine defoliator in Mediterranean forests. It affects a forest area around 1.5 million hectare just in Turkey and is the focus of much research. I have been studying PPM ecology and evolution since my masters; for my PhD thesis, I showed coexistence of two PPM species, European PPM Thaumetopoea pityocampa and Middle Eastern PPM T. wilkinsoni, in Turkey and a contact zone between them. This contact zone includes introgressed individuals which were revealed after comparing mitochondrial and nuclear sequences. However my PhD project aimed to include all PPM populations in Turkey and I did not concentrate particularly on the zone where I showed the contact between the two species. Therefore a further study was needed to learn more about the contact zone. I collaborated with Dr. Carole Kerdelhué of INRA in Montpellier and Dr. Christian Burban of INRA in Bordeaux as I did for my PhD project. I had made a further sampling in the contact zone and sent them to Montpellier for sequencing of a mitochondrial, a nuclear and 13 micrsosatellite genomic regions. Thanks to the EFIMED, I won a short scientific visit grant to visit Carole Kerdelhué in her lab in the Center for Biology and Management of Populations in Montpellier in autumn 2012.
The title of the project was “Studying Sequence Evolution and Population Genetics in Pine Processionary Moth Populations”. Our aim was to understand the nature of the hybridization between the two species. First of all, I looked for signs of hybridization in nuclear sequences. As in sexually reproducing species, both mother and father contribute genetically to the offspring genome, first generation hybrid individuals should have DNA sequences from two different species, in other words double peaks at chromatograms. I checked sequence chromatograms, especially at diagnostic sites (the sites where two species differ from each other), for double peaks. If I had found a stable double peak pattern, it would be easy to conclude that the two species are still hybridizing in nature. But it was not the case: the percentage of double peaks per diagnostic sites in a sequence was between 8% and 28% and peaks were rarely on the same nucleotide positions. Therefore manual sequence checks did not support an ongoing hybridization hypothesis.
Subsequently, I compared mitochondrial and nuclear sequences to see if they refer to same taxa. In my PhD thesis, I had found 3 individuals which had taxonomic incompatibility between cytoplasm and nucleus. This number rose to 20 after this project. All of these individuals were in the contact zone and it appears there is a mitochondrial introgression from the European species to the Middle Eastern one.
Our final aim was to define the introgression by using more data. For this purpose Laure Saune from the Center for Biology and Management of Populations in Montpellier had sequenced 13 microsatellite regions. During rest of my short scientific visit, I learned how to use programs such as Structure and NewHybrids to analyse microsatellite. I am still working on these analyses. When they finish, we will publish our results in a peer reviewed journal.
This project allowed us to develop our research and progress quite efficiently. So I acknowledge the EFIMED Short Scientific Visit Programme for funding this project. I also thank my supervisor Dr. Carole Kerdelhué for her great supervising and Dr. Christian Burban and Laure Saune for their theoretical and laboratory contributions. Final thanks to all people and lavenders of the Center for Biology and Management of Populations for their kindness, friendship, and good smell!
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