Predicting phenotypic variation in growth and metabolism of marine invertebrate larvae

Abstract

Understanding the mechanisms that establish variation in growth and metabolism is 12 fundamental in evolutionary and physiological ecology. Although a genetic basis is frequently 13 invoked to explain variation in performance, it remains challenging to study such processes in 14 marine animals due to the lack of genetically-enabled "model" organisms. The Pacific oyster 15 Crassostrea gigas is a species for which pedigreed genetic lines have been established. In this 16 study, a series of larval families were produced by crossbreeding pedigreed lines to yield large-17 volume larval cultures to provide sufficient biomass for biochemical and physiological analyses. 18Major phenotypic contrasts in larval growth rate were evident. A primary goal of this study was 19 to investigate the physiological bases for this variation in growth and to identify biomarkers that 20 are predictive of growth potential. To that end, measurements were undertaken to define the 21 relationship between rates of growth, respiration, and ion transport by the sodium-potassium 22 pump (in vivo Na + ,K + -ATPase activity). The relationship of respiration and ion transport during 23 larval growth showed that, on average, 17% of total energy demand was allocated to support ion 24 transport. Further analyses of total Na + ,K + -ATPase activity (in vitro enzyme assay) revealed that 25 41% of the total metabolic rate could be accounted for by this single process if all of the enzyme 26 was physiologically active. Significant biological variation was evident, however, when size-27 specific comparisons were made across different larval families. These differences were up to (i) 28 2.2-fold in ion transport rates; (ii) 2.8-fold in the allocation of energy to support the metabolic 29 demand of ion transport; (iii) 3.5-fold in total enzyme activity; (iv) 3.9-fold in the 30 physiologically active fraction of total enzyme; and (v) 3.1-fold in gene expression. These 31 differences among families highlight the need to distinguish genetic from environmental causes 32 of biological variation. Notably, for inferences of physiological changes based upon molecular 33 biological analyses, the measured rates of ion transport were not predicted from concurrent 34 measurements of gene expression or enzyme activity. Size-corrected rates of ion transport were 35 predictive of variation in growth rates among different larval families, supporting the application 36 of physiological rates of ion transport as a predictor of growth differences. Evolutionary 37 variation in physiological performance has important implications for understanding the ecology 38 of larval forms. Developing physiological indices will be of value in predicting growth and 39 metabolism and corresponding survival of larval forms of different genotypes in response to 40 environmental change.

Biochemical bases of growth variation during development: A study of protein turnover in pedigreed families of bivalve larvae (Crassostrea gigas)

“…In a previous study , larval families of C. gigas with faster growing phenotypes were shown to require less energy for the same size growth increment than slower growing families raised under the same environmental conditions. Because size-specific respiration rates are constant for larvae of C. gigas, and are independent of genotype Pan et al, 2016;Fig. 5 in the present study), differences in the cost of growth are dependent upon development time and not on differences in genotype-dependent, size-specific respiration rates.…”

“…1C). This genetic approach provided phenotypic contrasts in growth rate (Frieder et al, 2017;Pan et al, 2016), independent of alterations to environmental variables that impact growth and physiology, which are routinely conducted with wild-type animals (e.g. Frieder et al, 2018;Hawkins et al, 1986;Pan et al, 2015a;Podrabsky and Hand, 2000).…”

“…Respiration rates were measured as described previously (Marsh and Manahan, 1999), with modifications for larvae of C. gigas Pan et al, 2016). In brief, a known number of larvae (250-500 individuals, dependent on size) were placed in a sealed microbiological oxygen demand respiration vial that contained airsaturated, 0.2 μm ( pore size) filtered seawater.…”

“…Percent of ATP pool allocated to specific processes are: protein synthesis, 45% (from Fig. 3C, see Discussion for calculations); in vivo rates of sodium-potassium transport by Na + /K + -ATPase, 20% (from Pan et al, 2016); calcification (shell formation), 14% (from Frieder et al, 2017); protein degradation (PD), 3% (from Fig. 3C and Table 2; see Discussion for calculations).…”

“…Experimental cross-breeding of pedigreed lines of the Pacific oyster, Crassostrea gigas, is known to produce reproducible growth contrasts among different larval families (Curole et al, 2010;Hedgecock and Davis, 2007;Hedgecock et al, 1995Meyer and Manahan, 2010;Pan et al, 2015bPan et al, , 2016. In this study, pedigreed lines of C. gigas were used to produce larval families that, when reared under similar conditions of food and temperature, showed contrasting growth phenotypes.…”