Data from: The ontogeny of tolerance curves: habitat quality vs. acclimation in a stressful environment

Stressful environments affect life-history components of fitness through
(i) instantaneous detrimental effects, (ii) historical (carry-over)
effects and (iii) history-by-environment interactions, including
acclimation effects. The relative contributions of these different
responses to environmental stress are likely to change along life, but
such ontogenic perspective is often overlooked in studies of tolerance
curves, precluding a better understanding of the causes of costs of
acclimation, and more generally of fitness in temporally fine-grained
environments. We performed an experiment in the brine shrimp Artemia to
disentangle these different contributions to environmental tolerance, and
investigate how they unfold along life. We placed individuals from three
clones of A. parthenogenetica over a range of salinities during a week,
before transferring them to a (possibly) different salinity for the rest
of their lives. We monitored individual survival at repeated intervals
throughout life, instead of measuring survival or performance at a given
point in time, as commonly done in acclimation experiments. We then
designed a modified survival analysis model to estimate phase-specific
hazard rates, accounting for the fact that individuals may share the same
treatment for only part of their lives. Our approach allowed us to
distinguish effects of salinity on (i) instantaneous mortality in each
phase (habitat quality effects), (ii) mortality later in life (history
effects) and (iii) their interaction. We showed clear effects of early
salinity on late survival and interactions between effects of past and
current environments on survival. Importantly, analysis of the ontogenetic
dynamics of the tolerance curve reveals that acclimation affects different
parts of the curve at different ages. Adopting a dynamical view of the
ontogeny of tolerance curve should prove useful for understanding niche
limits in temporally changing environments, where the full sequence of
environments experienced by an individual determines its overall
environmental tolerance, and how it changes throughout life.