Andréa MODICA thesis defense

The interplay between selection and gene flow drives the attention of population genetics toward the mechanisms that regulate the lower limits of adaptation - spatial, temporal, and of genomic structure. Tree populations along altitudinal gradients exhibit a cline of spring phenology, a polygenic trait poorly understood in terms of fine regulation. Provenances of Fagus sylvatica in common garden show that trees at higher elevations are genetically early.

In this thesis I investigate the hypothesis that strong selective pressures at short spatial scales caused beech stands to evolve anticlinal genetic adaptation of spring phenology.

I investigated adaptation between four stands differing for environments, distance, and demographic past, testing an exome-capture panel of 34,889 SNPs with two single-locus and a multilocus test. Explicitly modelling of population history controlled demographic effects. Signals of selections were between all the stands and amounted to five loci and 17 haplotypes. A GPA studied the architecture of spring phenology at the stand level. A logistic model of Score ~ Day improved the precision of phenological time series. On a whole genome resequencing panel of 3,891,047 SNPs sequenced in 162 trees I found 47 unique QTLs associated with leaf-out. Years had distinct architectures. Significant QTLs mapped onto the exome capture data estimated the breeding value of the phenological traits in the stands along the same gradient, replicating the anticline.

Results suggest that local adaptation evolves rapidly, at very short spatial scales, and by changes at few loci within a polygenic architecture, nonetheless resulting in a cline of adapted phenotypes.

Jury members :

Oliver BRENDEL - CR, INRAE UMR Silva

Katharina Brigit BUDDE - CR, Northwest German Forest Research

Myriam HEUERTZ - INRAE BIOGECO

Elodie MAGNANOU - CR, CNRS and Sorbonne Université

Olivier PANAUD - PR, Université de Perpignan

Ivan SCOTTI - INRAE URFM