Figure legends:
Figure 1: Host-microbiome interactions are governed by the complex
interplay between host genotype, microbial genotype/community
composition, and the environment (A). The environment directly affects
both host and microbial genotypes/communities and microbes and host
reciprocally affect each other. Reciprocal transplants of seeds into
natal and non-natal environments, with and without microbes can reveal
when microbes are responsible for host adaptive responses. For example,
without microbes there is no pattern of adaptation (B), but when
microbes are manipulated in reciprocal transplant experiments you may
see either microbe-mediated local adaptation (C) when local plant
genotypes have higher fitness than foreign genotypes because of a
genotype-specific affiliation with locally important microbe(s) or
microbe-mediated adaptive plasticity (D) when local plant phenotypes
have higher fitness than foreign phenotypes as a result of interactions
with locally important microbes. Squares represent plants collected from
population 1 (P1), and circles represent plants collected from
population 2 (P2). Population 1 plants can either be transplanted into
their natal habitat (P1, represented by a square) or into a foreign
habitat (P2, represented by a circle), both with (C,D) and without (B)
microbes.
Figure 2: A fully factorial reciprocal transplant design can be used to
transplant seeds and microbes into home and away habitats to investigate
how microbes affect patterns of local adaptation. To definitively
attribute effects to microbes you need to include sterilized controls
(depicted here as a red line crossing out the microbial communities).
Squares represent plants and microbes collected from population 1 (P1),
and circles represent plants and microbes collected from population 2
(P2). Population 1 plants and microbes can either be transplanted into
their natal habitat (P1, represented by a square) or into a foreign
habitat (P2, represented by a circle).
Figure 3: The additional manipulation of moving microbes and plant
genotypes between sites can unravel if
GpxGmxE interactions dominate (A), in
this case positive effects of microbial symbionts would only be evident
in their natal habitat. Alternatively, if
GpxGm interactions dominate (B), plants
would still benefit from microbial symbionts when both were moved into
novel habitats. Microbe-mediated adaptive plasticity could be the result
of either microbes specialized for their particular habitat (C) or the
result of either direct or indirect (plant mediated) changes to
microbial function or shifts in community composition that affect plant
fitness. Microbe-mediated plasticity in important plant functional
traits, such as flowering time (D) might underlie microbe-mediated
adaptive plasticity, where microbes push flowering time phenotype into
an optimal range (depicted by the shading) for a given habitat. Squares
represent plants and microbes collected from population 1 (P1), and
circles represent plants and microbes collected from population 2 (P2).
Population 1 plants and microbes can either be transplanted into their
natal habitat (P1, represented by a square) or into a foreign habitat
(P2, represented by a circle) and vice versa.
Figure 4: Experiments to identify microbe-mediated adaptation will
require identifying a source of microbial inoculum (A) and determining
proper controls (B) for the experimental design. Another major
consideration is where the experiment will take place, evolutionary
ecology experiments with plants are typically performed in common
gardens (greenhouses or outdoors) or as reciprocal transplant
experiments.