title: The ontogeny of tolerance curves: habitat quality vs. acclimation in a stressful environment.
abstract: 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.
authors.affiliation: CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, 1919 route de Mende, F-34293, Montpellier Cedex 5, France.
authors.forename: Odrade
authors.initials: O
authors.lastname: Nougué
authors.affiliation: CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, 1919 route de Mende, F-34293, Montpellier Cedex 5, France.
authors.forename: Nils
authors.initials: N
authors.lastname: Svendsen
authors.affiliation: CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, 1919 route de Mende, F-34293, Montpellier Cedex 5, France.
authors.forename: Roula
authors.initials: R
authors.lastname: Jabbour-Zahab
authors.affiliation: CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, 1919 route de Mende, F-34293, Montpellier Cedex 5, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lenormand
authors.affiliation: CEFE UMR 5175, CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE, 1919 route de Mende, F-34293, Montpellier Cedex 5, France. luis-miguel.chevin@cefe.cnrs.fr.
authors.forename: Luis-Miguel
authors.initials: LM
authors.lastname: Chevin
mesh_terms: D000064:Acclimatization; D000220:Adaptation, Biological; D000818:Animals; D001156:Artemia / Q000254:growth & development / Q000502:physiology*; D004777:Environment; D005260:Female; D008954:Models, Biological; D054712:Salinity; D013312:Stress, Physiological
keywords: adaptive acclimation; changing environment; environmental tolerance curve; habitat quality; hazard rate; niche limits; phenotypic plasticity