Climate and genetic structure contributes to explain intraspecific genetic variation in defensive anatomical traits of a Mediterranean pine

The ability of trees to overcome the new environmental conditions will depend on the extant intraspecific variation in traits with adaptive value. Although genetic variation in life history traits related to productivity and abiotic stress has been better studied, little is still known about defensive traits. Resin ducts are the structures that store and produce the oleoresin in conifers, and because their role in resistance against biotic stress, they are a valuable proxy to study the defensive investment. In the current study, we explored the inducibility and the genetic variation of resin ducts among populations in Pinus pinaster and evaluated whether this variation is explained by the abiotic environment from the origin of populations. To meet our objectives, we used a clonal genetic collection of P. pinaster in a greenhouse experiment, including 79 clonally-replicated genotypes from 10 populations covering the species distribution range. We measured resin duct features in phloem and xylem in one clonal replicate and their inducibility in the other. Genetic variation among populations was explored by fitting mixed models, and correlation analysis were performed between resin duct features and climatic variables at the site of origin of populations after accounting for the population relatedness, which was quantified by genotyping 126 SNPs in the experimental material. We found that intraspecific genetic variation in the phenotypic expression of resin ducts was explained by the climate at origin. Moreover, we found that the differentiation of resin ducts in the xylem was inducible, although inducibility did not varied among populations.