Evol Ecol Res 10: 493-515 (2008)     Full PDF if your library subscribes.

Phenotypic diversity as an adaptation to environmental uncertainty

Matina C. Donaldson-Matasci,^1,2* Michael Lachmann² and Carl T. Bergstrom¹

¹Department of Biology, University of Washington, Seattle, WA 98195-1800, USA and  ²Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany

Address all correspondence to M.C. Donaldson-Matasci, Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
e-mail: donaldso@eva.mpg.de

ABSTRACT

Question: What is the general quantitative relationship between adaptive phenotypic diversity, or bet-hedging, and the environmental uncertainty that selects for it?

Mathematical methods: Building on the fitness set approach introduced by Levins, we develop a graphical heuristic for determining the optimal amount of diversity in a fluctuating environment. We use as our optimality criterion the expected long-term growth rate of a lineage.

Key insights: Each of the phenotypes in a polyphenic population may be seen as investing a certain proportion of its reproductive effort in each of the possible environments. A bet-hedging lineage that produces the phenotypes in just the right proportions – so that the overall reproductive investment in each environment matches the environmental frequencies – grows faster on average than other lineages. How much faster it grows than the resident population, and thus the strength of selection towards the optimal bet-hedging strategy, depends on how far the residents are from the optimal investment profile.

Predictions: A rigorous empirical demonstration that bet-hedging is adaptive requires a comparison of the degree of phenotypic diversification in similar populations subject to varying levels of environmental uncertainty. We confirm that bet-hedging should be observed only within a certain range of environmental variation; when the environment is more predictable than this, a phenotypic generalist would do better. We furthermore provide a simple method to calculate this range, based on the shape of the fitness trade-offs. Within this range, we predict a linear relationship between the frequency of phenotypes and the frequency of environments, independent of the shape of the trade-offs.

Keywords: bet hedging, fluctuating environment, generalist, life history, plasticity, polyphenism, specialist, trade-off.

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