DOI: 10.5061/dryad.bzkh189d3
title: Eco-evolutionary consequences of living with close relatives: Resistance to herbivores and climatic stress increases with investment into mycorrhiza in adult oaks

description: 1. Mycorrhizas are known to increase plant resistance to herbivores and
 climatic stress. However, it is unknown if particularly hostile
 environments select for increased investment of plants into mycorrhiza. 2.
 We studied hostile biotic environments: phylogenetically proximate
 neighbourhoods known to increase herbivory and pedoclimatic stress. In a
 common garden, we studied the resistances, tri-trophic interactions and
 microclimate of 28-years-old oaks (Quercus petraea), descending from
 provenances of contrasting phylogenetic neighbourhoods.  3. We
 found that oaks descending from phylogenetically proximate neighbourhoods
 had increased ectomycorrhizal enzymatic activities without affecting
 mycorrhization rate of root tips. We also found that increased
 ectomycorrhizal enzymatic activity decreased damages by one group of
 specialist herbivores (leaf-miners), without affecting another (galls) or
 generalists (ectophages). Consistently, descendants from phylogenetically
 proximate neighbourhoods showed decreased damage by leaf miners. We
 finally found that oaks descending from phylogenetically proximate
 neighbourhoods were most capable of maintaining leaf chlorophyll under
 heat-induced drought, reflecting their increased ectomycorrhizal enzymatic
 activities. 4. Synthesis. Overall, oaks living with closely related
 neighbours can rapidly evolve increased investment into ectomycorrhizas
 and thereby resistances to herbivores and climatic stress, ultimately
 facilitating coexistence among closely related neighbours. While
 phylogenetically diverse forests remain essential for maintaining
 biodiversity, the selection regimes in less diverse forests can be used as
 a source of native genotypes resistant to future climate change, rather
 than using exotic populations and species as a source pool.
description: Measurement of
 herbivory We inferred resistance of trees within the
 common garden to herbivores from low herbivory. We discriminated three
 feeding guilds: (1) galls: growth deformities on leaf surface by insect
 larva; (2) leaf mines: galleries formed between leaf epidermises by insect
 larva; (3) ectophagy: the partial or complete loss of leaf including
 epidermis. We assessed herbivory from 10 to 15 leaves, blindly selected
 from 40 to 60 leaves. To quantify herbivory we first reconstructed the
 initial leaf shape prior to damages. We took a grid of dots of 1 x 1 cm²
 and delimited on it the surface of the initial reconstructed leaf. Then we
 assessed the areas damaged by ectophages or leaf miners by counting the
 number of dots covering the damaged parts of the leaf.  We also counted
 the number of leaf mines and galls. For each leaf, we calculated the
 density of galls and density of leaf mines per cm², the proportion of area
 damaged by leaf miners, and the proportion of area damaged by ectophages.
 We then averaged each measure of leaf herbivory across leaves within trees
 and across trees within provenances. This highly standardized procedure
 enables us to avoid any bias in our measures. Also, the observer avoided
 measuring herbivory for the two trees of a provenance in a row to avoid
 bias. Measurement of the proportion of ectomycorrhizal
 root-tips, ectomycorrhizal enzymatic activity and density of root
 tips We
 inferred investment of trees within the common garden into ectomycorrhizas
 from the proportion of root tips with ectomycorrhizas and from the
 enzymatic activity of ectomycorrhizal root-tips. We assessed the
 proportion of ectomycorrhizal root-tips and density of root tips using the
 ground core taken in May 2018 using photo analyses (see appendix S8) and
 the ectomycorrhizal enzymatic activity from the ground core taken in
 September 2018 using high-throughput microplate assays (see appendix S8).
 Enzymatic activity, proportion of ectomycorrhizal root-tips and root-tip
 density were then averaged for each tree and averaged across trees within
 provenances. Measurement of temperature, altitude and tree
 height We inferred drought stress of the trees within
 the common garden from the air temperature at the surface of the crown at
 1 pm (crown temperature from here on), i.e. the warmest period of the day,
 on the 1st of September 2018. Note that trees had experienced 2 weeks
 without rain and with high temperatures during the days prior to the
 assessment of the crown temperature. Air temperature at the surface of
 plants can be used as a proxy of drought stress 57,58. Air temperature at the surface drives drought
 stress by increasing saturation water-vapour pressure and thereby
 saturation deficit of the atmosphere which increases water loss of plants
 by transpiration. We used the altitude and tree height as a proxy for
 ground-water access of leaves, i.e. high altitude reduces access to
 ground-water and height impedes transport of ground water to leaves. We
 assessed crown temperature and canopy altitude of the common garden from
 remotely sensed data59 (see appendix S9). Temperatures, heights and
 altitudes were averaged across trees within
 provenances.