Meeting Abstract

S8-1.4  Friday, Jan. 6  Phenotypic Plasticity and Allometry: New Models and Evolutionary Implications NIJHOUT, H. F.; Duke University

The sizes of body parts of many animals often appear to be related to each other by a power law called the allometric equation. Orderly scaling relationships among body parts depend on their patterns of relative growth, and simple analyses have shown that exponential growth can lead to size relationships that are well-described by the allometric equation. Exponential growth kinetics also allow for a simple biological interpretation of the coefficients of the allometric equation. However, body parts typically do not grow with exponential kinetics and then suddenly stop. Nor do they grow for the same amount of time. The consequences of realistic growth patterns on the form of the allometry equation have been little studied. I have derived new forms of the allometric equation that assume different growth kinetics (linear, exponential and sigmoidal), and that include differences in development time. These equations can be used to analyze the effect of different causes of variation in absolute size. Variation in size can be due to variation in the duration of development, the growth rate, or the initial sizes of parts. It turns out that the form of the allometric equation and the meaning of the coefficients depend on exactly how size variation comes about. The effects of phenotypic plasticity on allometry can now be examined in new and more precise ways because it is possible to partition the effects of environment on overall size variation and on specific parameters of relative growth. Sigmoid growth kinetics lead complex allometries and I will discuss why such allometries evolve to be linear (or nearly so) in nature.