[COLLOQUE] GENTREE Final Conference 27-31 January 2020 séance 16

GENTREE Final Conference :

Julie GAUZERE - University of Edinburgh · United Kingdom

GENTREE Final Conference 'Genetics to the rescue - managing forests sustainably in a changing environment'

27-31 January 2020, Avignon, France

http://www.gentree-h2020.eu/

Julie GAUZERE - University of Edinburgh · United Kingdom :Microgeographic adaptation and the effect of pollen flow on theadaptive potential of a temperate tree species.

Recent interest for microgeographic adaptation, i.e. adaptation atspatial scales compatible with substantial amount of gene dispersal,offers to reconsider the scale at which evolution occurs (Richardsonet al. 2014).

Whether gene flow is constraining or facilitating localadaptation at this fine spatial scale remains an unresolved question.

Too important gene flow would overwhelm the effects of naturalselection and decrease local adaptation along environmentalgradients.

Conversely, gene flow, and particularly long-distancedispersal events, could play a major role in resupplying the geneticvariation of populations and favouring the spread of beneficialalleles (Kremer et al. 2012).

Hence, the high dispersal capacities oftrees are often assumed to be the main process maintaining the largelevels of genetic variation measured in their natural populations.

However, evidences for microgeographic adaptation and thequantitative assessment of the impact of gene flow on adaptivegenetic variation are still limited in most temperate trees.

Here, wesampled 60 open-pollinated families of European beech (Fagussylvatica L.) from three natural plots, spreading along a shortelevation gradient (∼1.5 km) at the warm margin of this speciesdistribution.

We analysed the phenotypic and genotypic data of ∼2,300seedlings grown in a common garden. We focused on 11 potentiallyadaptive traits with significant heritabilities (Gauzere et al. 2016)and tested for signature of local selection on quantitative traitdifferentiation.

We then identified the offspring likely originatingfrom local or distant pollen immigration events and quantified therole of gene flow in increasing locally the additive variance oftraits under selection.

We found a significant signal of adaptivedifferentiation among plots separated by less than one kilometre,with local selection acting on growth and phenological traits.

Wefound that trees in the plots at high elevation, experiencing thelowest temperature conditions, flushed earlier and had a higherheight and diameter growth in our common garden than trees from theplot at low elevation.

Beech populations originating from higherlongitude or elevation have also been shown to be genetically earlierin provenance tests, suggesting that these populations evolvedphenological traits promoting a longer vegetation period.

At thissouthern margin of the species, the reduced allocation to stem growthat the low elevation plot is likely an adaptive response to drought,which has previously been described by comparing marginal vs centralbeech populations.

Consistently with theoretical expectations, ourresults suggest a beneficial effect of pollen dispersal by increasingthe genetic diversity for these locally differentiated traits.

Theseeffects were quantitatively high, with more than twice higher geneticvariance for immigrant than local offspring, although with largestandard errors around estimates.

Our results highlight that localselection is an important evolutionary force in natural treepopulations, and provide a strong evidence that adaptive geneticdifferentiation can occur despite high gene flow.

For the twogenetically differentiated traits, our analyses suggested abeneficial effect of pollen dispersal by increasing genetic diversityafter one episode of reproduction.

The findings suggest thatconservation and management interventions to facilitate movement ofgametes along short ecological gradients would boost geneticdiversity of individual tree populations, and thereby enhance theiradaptive potential.