Environmental effects on the detection of adaptation.

Detecting adaptation involves comparing the performance of populations
evolving in different environments. This detection may be confounded by
effects due to the environment experienced by organisms prior to the test. We
tested whether such confounding effects occur, using spider-mite selection
lines on two novel hosts and one ancestral host, after 15 generations of
selection. Mites were either sampled directly from the selection lines or
subjected to a common juvenile or to a common maternal environment,
mimicking the most frequent environmental manipulations. These environments
strongly affected all life-history traits. Moreover, the detection of
adaptation and correlated responses on the ancestral host was inconsistent
among environments in almost 20% of the cases. Indeed, we did not detect
responses unambiguously for any life-history trait. This inconsistency was due
to differential environmental effects on lines from different selection regimes.
Therefore, the detection of adaptation requires a careful control of these
environmental effects.