Category Archives: Population genetics

Nuclear microsatellite (nSSR) development for diploid annual mercury

Over 3,000 microsatellite sequences have been made available for marker development by Katie Ridou, the bioinformatician responsible of Mercurialis genome assembly. These sequences include only microsatellite regions with enough flanking sequence to design 20-bp PCR primers. Jonathan El Assad is using standard methods to PCR-test several primer pairs in a diverse panel of diploid Mercurialis annua covering its full range. The target is to develop a set of about 20 microsatellites that could be used in 2-3 multiplexes. This tool would be very useful to increase our understanding of Mercurialis annua demographic history and to evaluate the levels of inbreeding in current experimental evolution and quantitative genetics experiments.

Control crosses to study heterosis in colonization-front populations

Diploid Mercurialis annua from Central and Western Europe was the result of long-range colonization from ancestral populations in the eastern Mediterranean basin. Colonization-front populations are expected to have reduced fitness due to sequential bottlenecks during colonization. To test up to which point fitness in these populations can be increased by heterosis, polycrosses between different colonization-front populations in France, Spain and UK and between them and ancestral populations in Greece and Turkey are currently being performed at the UNIL greenhouses. This seed material will be used in a quantitative genetic experiment to be installed in Switzerland (under Atlantic/continental climate) and Spain (under Mediterranean climate) in spring 2015.

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Crossing scheme and open “boxes” used for crosses at UNIL

Full exome capture experiment

A new full-exome capture assay (ca. 48 Mbp of sequence) has been designed and will be used for sequencing of 48 Mercurialis accessions in the framework of a Senior Marie Curie Project by Dr. Santiago C. González-Martínez. This assay covers the over one hundred thousand exons found in the M. annua diploid genome and were identified using state-of-the-art bioinformatics by postdoc Kate Ridou. The assay is also intended to sequence sex-linked regions and random non-coding portions of the Mercurialis genome. The 48 accessions that will be sequenced with this assay have been collected from both ancestral and colonization-front of the species (see map below). Deep sequencing of these materials would allow to determine the genetic make-up of colonization-front populations in diploid Mercurialis annua.

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The 48 accessions included in the M. annua gene capture experiment

Gene flow experiment

Preliminary analyses for the gene flow experiment have been completed. This experiment, conducted by postdoc Anne-Marie Labouche, considers the effects of pollen limitation and pollen competition on offspring number and quality as a function of plant density. Apart from demonstrating pollen limitation in Mercurialis, the experiment showed larger pollen flow distances than expected and several other interesting features related to M. annua mating system.

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Experimental arrays of wind-pollinated Mercurialis annua, in which distance from a pollen source regulates the intensity of pollen competition.