Meeting Abstract

S3.4  Monday, Jan. 4  Learning, developmental plasticity and the evolution of morphological asymmetry PALMER, A. Richard; University of Alberta rich.palmer@ualberta.ca

Evolution by natural selection requires three steps. New variants of organisms: must arise, must have an impact on fitness (survival or fecundity), and must (ultimately) be heritable. The first step – how new variants arise – remains controversial. Traditionally, the most significant source of new phenotypes was believed to be novel genotypes (mutants or recombinants) – a ‘genotype-precedes-phenotype’ mode of evolution. But developmental plasticity – the same genotype yields different forms in different environments – may be a more important source of new variants than generally recognized. The absence of heritable variation for direction of asymmetry in species that show a random mixture of asymmetric forms (i.e., equal numbers of right- and left-handed forms), identifies a unique phenotype – ‘direction of asymmetry’ – for which there is no genotype and which therefore permits tests of alternative modes of evolution. A wide-ranging survey of asymmetry variation within and among species of animals and plants offers some of the strongest evidence to date for widespread occurrence of a ‘phenotype-precedes-genotype’ mode of evolution. In addition, the tendency of many animals to learn (e.g., handed behavior) may facilitate both the origin and the amplification of right-left morphological differences via developmental plasticity. Such an interplay between learning and developmental plasticity might greatly enhance the rate of morphological evolution. Anecdotal observations, experimental studies, and both ontogenetic and phylogenetic evidence all suggest that handed behaviors play (or played) an important role in the development and evolution of phenotypically significant morphological asymmetries.