Questions: Why and how do relative body size and density influence the expression of polyphenism?

Phenomenon studied: Facultative paedomorphosis in salamanders is a polyphenism producing two alternative adult phenotypes, paedomorph and metamorph.

Mathematical Methods: Evolutionary game model; ESS and CSS analysis justified by population genetics.

Key assumptions: The fitness of each morph is determined by density, relative body size, and the frequencies of phenotypes. Individual body size is environmentally determined. Each strategy is denoted by the probability of becoming paedomorphic as a function of body size.

Conclusions: Large animals become paedomorphic when density is low, small animals become paedomorphic when density is high, and the frequency of paedomorphosis is minimized when density is intermediate. These results are consistent with current empirical studies, and make testable predictions for future research on this and other polyphenisms.