Data for: Adaptive, maladaptive, neutral, or absent plasticity: Hidden caveats of reaction norms

Adaptive phenotypic plasticity may improve the response of individuals
when faced with new environmental conditions. Typically, empirical
evidence for plasticity is based on phenotypic reaction norms obtained in
reciprocal transplant experiments. In such experiments, individuals from
their native environment are transplanted into a different environment,
and a number of trait values, potentially implicated in individuals’
response to the new environment, are measured. However, the
interpretations of reaction norms may differ depending on the nature of
the assessed traits, which may not be known beforehand. For example, for
traits that contribute to local adaptation, adaptive plasticity implies
non-zero slopes of reaction norms. By contrast, for traits that are
correlated to fitness, high tolerance to different environments (possibly
due to adaptive plasticity in traits that contribute to adaptation) may,
instead, result in flat reaction norms. Here we
investigate reaction norms for adaptive versus fitness-correlated traits,
and how they may affect the conclusions regarding the contribution of
plasticity. To this end, we first simulate range expansion along an
environmental gradient where plasticity evolves to different values
locally and then perform reciprocal transplant experiments in
silico. We show that reaction norms alone cannot inform us whether the
assessed trait exhibits locally adaptive, maladaptive, neutral or no
plasticity, without any additional knowledge of the traits assessed and
species’ biology. We use the insights from the model to analyse and
interpret empirical data from reciprocal transplant experiments involving
the marine isopod Idotea balthica sampled from
two geographical locations with different salinities,
concluding that the low-salinity population likely has reduced adaptive
plasticity relative to the high-salinity population. Overall, we conclude
that, when interpreting results from reciprocal transplant experiments, it
is necessary to consider whether traits assessed are locally adaptive with
respect to the environmental variable accounted for in the experiments, or
correlated to fitness.