  Adaptation to one environment often results in fitness gains and losses in
other conditions. To characterize how these consequences of adaptation depend
on the physical similarity between environments, we evolved 180 populations of
Saccharomyces cerevisiae at different degrees of stress induced by either salt,
temperature, pH, or glucose depletion. We measure how the fitness of clones
adapted to each environment depends on the intensity of the corresponding type
of stress. We find that clones evolved in a given type and intensity of stress
tend to gain fitness in other similar intensities of that stress, and lose
progressively more fitness in more physically dissimilar environments. These
fitness trade-offs are asymmetric: adaptation to permissive conditions incurred
a smaller trade-off in stressful conditions than vice versa. We also find that
fitnesses of clones are highly correlated across similar intensities of stress,
but these correlations decay towards zero in more dissimilar environments. To
interpret these results, we introduce the concept of a joint distribution of
fitness effects of new mutations in multiple environments (the JDFE), which
describes the probability that a given mutation has particular fitness effects
in some set of conditions. We find that our observations are consistent with
JDFEs that are highly correlated between physically similar environments, and
that become less correlated and asymmetric as the environments become more
dissimilar. The JDFE provides a framework for quantifying evolutionary
similarity between conditions, and forms a useful basis for theoretical work
aimed at predicting the outcomes of evolution in fluctuating environments.
