Data from: Field evidence for a rapid adaptive plastic response in morphology and growth of littoral and pelagic brook charr: a reciprocal transplant experiment

1. Phenotypic plasticity, a process by which individuals modify their
morphology, physiology, or behaviour in response to environmental changes,
can be seen as the first step in adaptive evolution. Phenotypic plasticity
is adaptive if two conditions are met: (i) the phenotype is associated
with an environment (plastic response) and (ii) the phenotype–environment
association increases individual fitness (adaptive response). 2. Using a
reciprocal transplant experiment, we tested the hypothesis that functional
morphological responses are correlated with growth at two organizational
levels (between and within ecotypes) in brook charr. 3. Four-month-old
individuals from four littoral and four pelagic families raised in the
laboratory were transferred into eight littoral (3 m × 4 m × 1.5 m depth)
and eight pelagic (3 m × 4 m × 6 m depth) lake enclosures for a period of
12 weeks. 4. Fin length (the main discriminant trait of the littoral and
pelagic ecotypes) was less plastic than body shape. Growth was higher in
the pelagic than in the littoral habitat, but offspring from littoral and
pelagic parental origins did not experience higher growth in their
respective habitats (comparison between ecotypes). The body shape of most
individuals transplanted to their reciprocal environment shifted toward
the form expected in that environment. This plastic response in body shape
was functionally correlated with growth within ecotypes, but only in the
littoral habitat. Furthermore, the within-ecotype variance of both
morphological traits and growth were higher in the littoral than in the
pelagic habitat. 5. Small phenotypic differences could have direct
consequences on fitness in the less favourable habitat, inducing higher
inter-individual variance in growth and stronger phenotype–growth
associations. We suggest that phenotypic accommodation and cryptic genetic
variation, two mechanisms previously proposed as mechanisms involved in
distinct situations, could be simultaneously involved to hasten the
process of adaptive evolution in an unfavourable environment.