Rapid Evolution of Gastrulation Mechanisms in a Sea Urchin With Lecithotrophic Larvae

Abstract

No.8 Gastrulation is the earliest and most fundamental morphogenetic process in metazoan development. Cell movements that occur during gastrulation establish the topological relationship between cells of the primary germ layers, setting the stage for later inductive interactions. Modes of gastrulation in extant phyla and classes are remarkably diverse (Kume and Dan, 1968;Ballard, 1976), suggesting that modifications in gastrulation have been an important component in the evolution of animal development. Very little, however, is known about the time scales over which evolutionary modifications in gastrulation occur or the consequences of such changes on body plan organization. This study investigates evolutionary changes in gastrulation within the Echinoidea (sea urchins, sand dollars, Abstract. -This study documents evolutionary modifications in mechanisms of gastrulation in Heliocidaris erythrogramma, an echinoid with lecithotrophic larvae. Radially symmetrical cell rearrangements and changes in cell shape drive elongation ofthe archenteron in the ancestral mode of echinoid gastrulation. Cell marking experiments indicate that in H. erythrogramma, however, prolonged movement of cells over the ventral lip of the blastopore accompanies extension of the archenteron. Evolutionary modifications to archenteron extension in H. erythrogramma thus include utilization of a different type of cellular movement as well as the imposition of dorsoventral asymmetry in cellular movements. The conservation of gastrulation mechanisms among phylogenetically divergent echinoids with planktotrophic development suggests that the plesiomorphic condition has persisted at least 250 million years and perhaps much longer. Yet H. erythrogramma diverged from an ancestor with planktotrophic development only about 10 mya, indicating that morphogenetic mechanisms of early development can undergo substantial evolutionary changes, even after long periods of stasis.

Life history evolution and comparative developmental biology of echinoderms

“…Large eggs develop to metamorphosis more quickly than small eggs of echinoderms (Emlet et al 1987;Levitan 2000). Very large, yolk-rich eggs may have altered patterns of spindle formation, cleavage, and segregation of morphogenetic determinants compared with small eggs (Gilbert 2000;Wray and Raff 1991a). The evolution of very large eggs is also the necessary precursor to the evolution of highly derived styles of nonfeeding or brooded larval development (Wray and Raff 1991b).…”

Molecular Phylogenetic Analysis of Life-History Evolution in Asterinid Starfish

“…This rarity suggests that the transition from feeding to nonfeeding larvae is rapid. Other evolutionary changes in larval development may be rapid as well (Wray and Raff 1991). Some branches in the phylogeny along which life-history changes must have occurred (Fig.…”

Ontogenetic Torsion and Protoconch Form in the Archaeogastropod Haliotis kamtschatkana: Evolutionary Implications

“…However, many studies on a variety of animals have shown that members of a related group (even congeneric species) can show marked differences in early development, particularly but not exclusively when nutritional sources for the embryo are different (Elinson 1987;Raff et al 1990;Wray & Raff 1991;Janies & McEdward 1993;Bolker 1994). These and other empirical developmental data continue to discredit Haeckelian interpretations of ontogenetic transitions (see Alberch 1985).…”