DISSERTATION RESEARCH: The evolution of major life-history transitions: a transcriptomic analysis of developmental shifts in echinoids

University Of California-Davis, Davis CA

Investigators

Abstract

This project will investigate the genetic basis of alternate types of larval development. Many ocean-dwelling animal species have a free-living larval stage, which is generally one of two major types. They are either long-lived, feeding larvae that develop over the course of months to years, or short-lived, non-feeding larvae that develop in a matter of hours to days. Larval type (feeding or non-feeding) has many important ecological and evolutionary ramifications, as it influences the size of species' ranges, connections between populations, and the potential for speciation and extinction. Although evolutionary transitions from feeding to non-feeding larvae occur frequently, we know little about the genetic changes that underlie these transitions. This project will test the hypothesis that larval development type depends upon certain maternal effects: messenger RNA (mRNA) in the eggs. The researchers will collect mRNA sequencing data from eggs of sand dollar and sea biscuit species to determine if differing developmental types are associated with different maternal mRNA. In addition, the project will support the training of minority undergraduate researchers and the creation of a public exhibit at a nature center. Preliminary research on two closely related species of echinoderm sea biscuits, which exhibit different larval developmental modes, demonstrated that larval developmental patterns are strongly driven by maternal factors. Although such maternal effects also drive the developmental patterns of larvae in several other systems, the underlying cause of this maternal effect remains unclear. This project will test the novel hypothesis that the strong maternal effect on development is due to differences in maternally deposited mRNA. The researchers will sequence the maternally deposited mRNA from unfertilized eggs of several closely related species pairs of sand dollars and sea biscuits that have alternate larval types. These data will also be used to create a time-calibrated phylogeny to correct for phylogenetic signal. Using these data, the project will determine how maternally deposited mRNA differs in eggs of feeding and non-feeding echinoderm larvae, and how those differences influence the evolution of alternate developmental pathways.