Plasticity in forest trees: a brief review and a few thoughts

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Kelley Eaton
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1 Plasticity in forest trees: a brief review and a few thoughts GEA, Montpellier, 2008 from INRA plasticity team: C. Bastien, V. Jorge, A. Martinez, L. Paques, P. Rozenberg, L. Sanchez.

2 Plasticity has become a popular subject, frequently in use in relevant scientific literature Unfortunately it is not always the case this use is coherent with academic definition, even if most authors agree with such academic definition

Plasticity is often found in biodiversity versus global change debate Thuiller et al put it right when pinpointing that the role of plasticity as a buffer against global

3 Plasticity is often found in biodiversity versus global change debate Thuiller et al put it right when pinpointing that the role of plasticity as a buffer against global warming has not been fully appreciated most studies assessing future climate impacts on diversity do not consider individual based plasticity but whole population reactions

4 Original ecotypic differentiation re-appeared mostly at within-population level in common garden experiments for growth, biomass and hydraulic architecture ( microsatellites Weak genetic differentiation among populations (DNA Significant experimentally driven drought effects suggest plasticity Constitution of experimental populations: pooled seedlings from different open pollinated mothers

5 Over and above definitions how well family average, provenance or species performances over environmental ranges predict plasticity? It would ultimately depend on the genetic nature of plasticity, if purely additive, family or sib means would fairly predict parental plasticity over environments if partially or mostly non-additive, as expected from pleiotropic or/and epistatic systems (i.e. physiological plasticity), groups NoR would not provide unbiased predictors of individual plasticity Between-group heterogeneity from differences in inbreeding, sampling, foundational effects would further affect the quality of group NoR as predictors of individual plasticity How to tell apart within-group genotypic variation from plasticity?

6 We have however an indirect measure of the importance of phenotypic plasticity in forest tree species many successful genetic transfers over ample latitudinal and climatic ranges Authors state that to be able to assess such phenotypic plasticity in forestry we need clonal replication

7 Many authors have already embraced multi-site clonal tests for plasticity experiments in plants Undoubtedly, truly genotype by NoR can be drawn over environmental factors Conformity with definitions of individual genotypic plasticity However: do ex-situ field tests capture all relevant ecological and developmental factors with an eventual role in plasticity? for slow-growing long generation time species, like forest tree species, to what extend this ex-situ spatial plasticity presages temporal plasticity?

8 Relevant variation in PP to adaptation could be partially concealed in complex ecological networks, where species dynamic interactions and multiple interacting physical factors may reduce directional expression of individual plasticity Assessment of plasticity needs this multidimensional ecological lecture

9 Should we go towards in-situ measures of developmental NoR, where individual phenotypic records are persistent over time: like in fine-scale wood formation? in-situ: taking into account the ecological complexity developmental: taking into account plasticity that s relevant to tree s life individual: conform with plasticity s definition However, if such an in-situ measure may help to disentangle the respective roles of phenotypic variation and genetic variation in evolution we should not neglect the power of ex-situ tests to infer the genetic variation and determinism behind proposed measure

10 Why ex-situ tests? the opportunity of selection experiments Selection experiments as probes of genetic architecture and able to mimic natural selection Many selection programs in forestry have attained maturity with several generations and retrospective measures in multi-site experiments are not rare (supporting temporal ( measures

11 Selection experiments in model species have already established that: plasticity for studied traits is heritable and can be selected for plasticity for studied traits can also evolve as correlated response plasticity is likely the result of the expression of multiple interacting loci Selection experiments, however, are insufficient to allow distinction between pleiotropy and epistatic models. Other approaches are needed, like molecular or expressional methods, always based on individual measures with full family records

12 Some closing thoughts are to use individual based quantitative approaches that can be easily linked to molecular, expressional and/or ecophysiological studies later on to study plasticity of temporal retrospective NoR and over multiple traits (to address the question of plasticity as a trait vs ( trade-off plasticity as a to study the genetic determinism of plasticity traits taking advantage of highly monitored multi-site selection experiments (do not neglect vast evaluation network in ( conifers commercial to study adaptive relevance of plasticity traits in-situ upon same traits as ex-situ experiments (look for conspicuous climate ( gradients

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