Investigating complex larval traits in a reef-building coral

Dispersal of the majority of large benthic marine invertebrates relies on a planktonic phase of the life cycle dispersed by ocean currents. Patterns and spatial scales of larval dispersal drive biogeographic distributions, genetic connectivity and population and community dynamics. Biological parameters that drive dispersal potential include larval traits such as the onset and length of competence, the ability of larvae to metamorphose in response to a specific environmental cue, and the rate of energetic storage depletion. This dissertation examines complex larval traits of a reef-building coral, Acropora millepora, giving insight into how larval trait variation and molecular pathways may contribute to the propensity to disperse. First, I examined whether or not light color (wavelength) acts as a cue to influence the likelihood of settlement and metamorphosis in two species of reef-building coral. I found that exposure to different colored lights impacts the propensity to metamorphose when exposed to chemical settlement cues, and these differences in behavior reflect wavelengths of light roughly associated with their respective habitats. Second, I characterized gene expression differences between three larval fluorescent color morphs in order to elucidate the functional significance of color variation in larvae. I found that red fluorescent larvae have gene expression profiles that correlate with gene expression profiles associated with coral larval thermal tolerance and diapause in other organisms. This suggests that red fluorescent larvae may be physiologically able to exist in the water column longer, potentially dispersing longer distances. Third, I described patterns of gene expression through development and correlated these patterns to competence and fluorescence. This revealed that larval maturation associated with competence is correlated with gene expression of neuropeptide signaling, ion transport and GPCR signaling. Environmental perturbation, such as temperature, may affect these pathways, which could alter larval dispersal dynamics in the sea. Finally, to complement these correlative studies, I developed the first method of genomic manipulation in reef-building corals. Utilizing the CRISPR/Cas9 system induced targeted mutagenesis in candidate genes associated with larval dispersal traits. This work is foundational to study gene functions in an ecological context, which will greatly improve our understanding of coral biology.