Phylogenetic and biogeographical patterns in defensive strategies and quantitative allocation to chemical defences in Palaearctic and Nearctic pine trees

Aim: Using pine trees as a long-lived woody plant model, we analysed the extent to which constitutive and induced allocation to chemical defences were conserved across the phylogeny, and tested the hypothesis that patterns of defensive allocation and defensive strategies differ between Palaearctic and Nearctic pines.Location: Common-environment study with Palaearctic and Nearctic pine species.Methods: We grew 17 pine species (eight Palaearctic and nine Nearctic) in a common environment and measured the stem and needle concentrations of phenolics and non-volatile resin, two major quantitative chemical defences in pines. In particular, we studied the constitutive allocation to chemical defences (in control plants) and the potential inducibility of those traits in response to elicitation with hormonal analogues of the jasmonic acid (methyl jasmonate) and salicylic acid (benzothiadiazole) pathways of plant defence against herbivorous insects and pathogens.Results: We found a strong phylogenetic signal in the constitutive concentration of phenolics in the needles and resin in the stem, but not elsewhere. We found that Nearctic pines showed 70% greater concentration of constitutive needle phenolics than Palaearctic species. In contrast, the inducibility potential of defences did not differ between Nearctic and Palaearctic pine species.Main conclusions: Our findings suggest that macroevolutionary history (phylogeny and biogeographical origin combined) has played an important role in the evolution of needle constitutive defences among pine species, but not in that of induced defences. Specifically, constitutive allocation to pine chemical defences seems to be well preserved across the phylogeny. In contrast, the inducibility of chemical defensive traits was evolutionarily labile and may depend more on the particular climate, biotic interactions and resource availability in each species’ range.Research was partly funded by the Spanish Ministerio de Ciencia e Innovación, projects Consolider-Ingenio MONTES (CSD2008-00040), COMPROPIN (AGL2010-18724) and FENOPIN (AGL2012-40151-C03-01) and the Severo Ochoa Program for Centres of Excellence in R+D+I (SEV-2012-0262). X.M. received financial support from the Postdoctoral Fulbright/Spanish Ministry of Education grant program; A.G.-V. was funded by a JAE-Doc (JAE-Doc030) post-doctoral fellowship from the CSIC.Peer reviewe