Physiology and biochemistry of food limitation in marine invertebrate larvae.

摘要

For high fecundity organisms, the number of offspring that survive to adulthood are very few. The mechanisms of individual-based survival remain of great interest in biology. In this dissertation, larval survival was examined by taking an integrative approach, from organismal physiology to molecular biology.Large numbers of larvae from sea urchins (Lytechinus pictus) and bivalve mollusks (Crassostrea gigas) were experimentally tested for starvation tolerance. Theoretically, survival during the "critical period" of early feeding is low in the absence of appropriate particulate foods. Empirically, survival was measured in large-volume culture experiments (200-l). Analysis revealed that some larvae could resist starvation for over 40 days. Bivalve larval families of known genotype had large survival differences despite similar biochemical contents and metabolic rates. Sea urchin larvae had similar physiological capacities to survive extended periods of starvation while still conserving organic mass and maintaining metabolic rates. Importantly, such "starved" larvae for both species subsequently recovered when fed showed normal morphological and physiological characteristics. For instance, sea urchin larvae that were starved for 18 days prior to feeding were subsequently able to undergo metamorphosis. For bivalve larvae, specific genotypes with high starvation resistance were also the families that showed high growth rates when fed. The significance of this finding is that "one genotype fits all" in that the same genotype showed the best performance under poor and good conditions (starved or fed ad libitum).Exogenous nutrition from dissolved organic matter has long been speculated to provide energy for marine invertebrates. In sea urchins, amino acid transporter proteins were localized ultrastructurally in subcellular compartments of unfertilized eggs and in larval ectoderm in later development. Genes of the same family were also identified in bivalve larvae. In same-aged bivalve larvae of different sizes (phenotypic contrasts), high growth rates were related to differential gene expression.The major finding from this dissertation is that physiological mechanisms of survival are genotype-related. This has important consequences for the adaptive basis of survival of early life history stages. Predicting which phenotype has the adaptive ability to survive in rapidly changing environments is a critical requirement for understanding ocean ecology.