120.2 Saturday, Jan. 7 High genotype-dependent mortality at metamorphosis in the Pacific oyster PLOUGH, L.V*; HEDGECOCK, D.; University of Southern California; University of Southern California email@example.com
Settlement and metamorphosis is a critical period in the life cycle of marine invertebrates, during which larvae undergo substantial morphological, sensory, and genetic changes regulated by distinct developmental processes. High mortality during this transition has been well documented for a variety of marine invertebrates and is generally interpreted as occurring post-settlement and environmentally derived; little is known, however, about how mortality may occur during the process of metamorphosis itself, and what role genotype and endogenous genetic variation play in this mortality. Previous work has shown that the Pacific oyster, Crassostrea gigas, carries a high load of deleterious recessive mutations inferred from massive distortions of zygotic, marker segregation-ratios in inbred families, which cause substantial genotype dependent mortality. Here I present data from multiple studies examining the stage-specific expression of these deleterious loci and the resultant genotype dependent mortality during the life-cycle, particularly at metamorphosis, using QTL mapping methods to identify regions of the genome under viability selection. We find first, that ½ of the loci causing genotype dependent mortality act during metamorphosis. Further dissection of mortality during metamorphosis through careful sampling of settlers and larvae revealed a mutation causing selection during metamorphosis, possibly affecting the morpho-genetic pathway, while another mutation caused a delay in metamorphosis or prevented metamorphosis from beginning, suggestive of a defect in the competence pathway. Overall, selection during the larval-juvenile transition appears to be confined to the induction of metamorphosis and metamorphosis itself, which highlights the importance of understanding the developmental pathways associated with this critical transition.