The Evolution of Developmental Plasticity in Reproductive Characteristics: An Application of the "Adaptive Coin-Flipping" Principle

Abstract

Reproductive characteristics such as egg size and clutch size can be highly variable within populations of cold-blooded vertebrates (e.g., amphibians). Such variation makes the idea of an optimal mean reproductive characteristic difficult to defend. The concepts of canalizing and decanalizing selection, which result, respectively, in a buffered or unbuffered developmental system, can be responsible for the maintenance of specific levels of intrapopulational variation. Different types of variation, such as intraclutch and interclutch variation in egg size, are distinguished. As an adaptation to an unpredictable offspring environment, a single female may produce a seemingly maladaptive egg as a result of selection operating to maintain developmental plasticity in the vitellogenic process. The developmental mechanisms which generate such seemingly stochastic variation are called "adaptive coin-flipping." The properties of the developmental coin (which can be 2-sided or many-sided, fair or weighted) can evolve as a result of differences among individuals in sensitivities of vitellogenesis to environmental variation or a result of individual differences in unresolvable developmental noise. Evidence is cited for the heritable nature of such variation in the properties of coins, and the significance of a developmental coin-flip for ecological processes in general is discussed.