Meeting Abstract
Morphological novelty is often thought of as the evolution of an entirely new body plan or the addition of new structures to existing body plans. However, novel morphologies may also arise through modification of organ systems within an existing body plan. The evolution of novel scaling relationships between body size and organ size constitutes such a novel morphological feature, and morphological novelty can arise through evolutionary changes in the relative growth of body parts. Insects provide excellent examples of evolutionary novel allometries, displaying some of the most exaggerated traits in the animal world, e.g. eyes on the ends of long stalks, forelegs longer than twice the body length, and horns that emerge from the head and thorax. Experimental studies have demonstrated that there is genetic variation for allometries and that scaling relationships can evolve under artificial selection. A natural question that arises is: what kinds of changes in the underlying developmental processes can yield shifts in scaling relationships? We will discuss how changes in nonlinear growth kinetics can give rise to novel allometric relationships. Using wing-body scaling in Manduca sexta, we show that the size attained by wings depends on parameters that influence both body growth and wing growth. Several different combinations of parameters can yield similar scaling relationships. We describe how parameters change under directional and stabilizing selection on body size, wing size and relative wing size. Finally, we demonstrate how novel morphologies can arise by evolutionary change in growth kinetics.
