Meeting Abstract

P2.109  Monday, Jan. 5  Doubling Egg Volume to Test for Reversible Evolution of Larval Form and Effects of Eggs Size on Heterochrony BERTRAM, Douglas F.; PHILLIPS, Nicole E.; STRATHMANN, Richard R.*; Environment Canada; Victoria Univ. Wellington; Univ. of Washington rrstrath@u.washington.edu

Doubling volume of the small eggs of the purple sea urchin Strongylocentrotus purpuratus by egg fusion produced larvae more similar in form to those from normal large eggs of the green sea urchin Strongylocentrotus droebachiensis. This result mirrors previous experiments in which larvae from half embryos of green urchins were more similar to normal larvae of purple urchins. Thus effects of egg size on larval form are similar against either species genetic background and are evolutionarily reversible. Development of the juvenile rudiment was not accelerated relative to the larval body by experimentally doubling the volume of eggs of purple urchins. In larvae from normal-size eggs, development of both larval body and rudiment were accelerated in green urchins (with large eggs) relative to development in purple urchins (with small eggs), but with greater acceleration of the larval body, so that the rudiment of larval green urchins was initiated at a later stage, even though at an earlier age. Both species exhibited similar plasticity in timing of rudiment development in response to food supplies. Although heterochronic plasticity in development of the larval body and juvenile rudiment in response to food may be a basis for similar heterochronic changes in the evolution of non-feeding larvae, experimental and evolutionary changes in egg volume did not directly accelerate rudiment development of these feeding larvae.