Meeting Abstract
Allometry refers to variation in organismal shape that correlates with size. It is a form of integration that is special because variation in size is ubiquitous within and between species. Allometry is so commonly observed that it is routinely removed from analyses or invoked as an explanation for evolutionary change. In this case, familiarity is confounded with understanding because rarely do we know the mechanisms by which shape correlates with size or understand their significance. As with other forms of integration, allometric variation is generated by variation in developmental processes that affect multiple traits, resulting in patterns of covariation. Given this perspective, we can dissect the genetic and developmental determinants of allometric variation. Our work on the developmental and genetic basis for allometric variation in craniofacial shape in mice and humans has revealed that allometric variation is determined by multiple processes that are related to growth and timing which may have different effects on trait associations. Different measures of size are often associated with different patterns of allometric variation. Further, many mutations result in covarying effects on size and shape that differ markedly from expected allometric patterns. Nutritional stress produces timing-dependent effects of allometric variation, and growth deficient mice treated with growth hormone recover shape in a manner that depends on the timing of treatment. Finally, the genetic determinants of allometric variation are very complex and involve mainly genes with little obvious relationship to the central determinants of growth. These results question the view of allometry as a coherent phenomenon distinct from morphological integration more generally.
