Phenotypic plasticity and optimal timing of metamorphosis under uncertain time constraints |
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Authors: | Volker H W Rudolf Mark-Oliver Rödel |
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Institution: | (1) Department of Animal Ecology and Tropical Biology (Zoology III), Theodor-Boveri-Institute (Biocenter of the University), D-97074 Würzburg, Germany;(2) Department of Zoology, Mainz University, Saarstrasse 21, D-55099 Mainz, Germany;(3) Present address: Department of Biology, University of Virginia, 243 Gilmer Hall, Charlottesville, VA 22904-4327, USA |
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Abstract: | Life-history theory suggests that optimal timing of metamorphosis should depend on growth conditions and time constraints
under which individuals develop. Current models cannot make reliable predictions for species in ephemeral habitats where individuals
often face an increasing mortality risk over time because these models assume time-invariant mortality rates (i.e., daily
mortality rates remain constant) and fixed seasons. We examined the plasticity of growth, development, and body mass at metamorphosis
in tadpoles of the tree-hole breeding frog Phrynobatrachus guineensis in relation to an unpredictable time constraint in the field and in controlled experiments along a fixed density and food
gradient. Mean mass and age at metamorphosis of sibships were positively correlated with per capita food level. Based on our
results, we developed a simple model of the optimal timing of metamorphosis under time-dependent mortality rates showing that
development rates are not only adjusted to growth conditions but also to time-variant mortality rates. The increasing mortality
rate represents a time constraint that favors a reduced larval period, but because it is based on probabilities of survival
it allows a trade-off between development time and mass. We extend this model to different types of time constraints and show
that it can predict the range of documented reaction norms. Differences between species in␣the correlation of age and mass
at metamorphosis may have evolved due to differences in their time-variant mortality rates. |
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Keywords: | Amphibians Complex life cycles Development Growth rate Mortality risk Desiccation risk Adaptation Life history evolution |
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