Cost of Growth in Cells and Organisms: General Rules and Comparative Aspects

Abstract

In a crude fashion it can be said that metabolizable energy (M) is partitioned into metabolic work, paid for by 'oxidations' (R), and 'assimilation', i.e. production (P), so that M = R+P. However, a fraction of R is required to meet the expenses of production and if these expenses represent, Joule for Joule, a constant proportion of the amount produced, then Rt = Rm+cP, where Rt = total metabolic expenditures, Rm = metabolic expenditures for maintaining the non-producing organism, and cP = Rp = metabolic expenditures connected with the processes of production. The partitioning of metabolizable energy into R and P as well as into Rm and Rp may vary depending on the phylogeny and life-history of the species concerned and on ecological circumstances. Thus selection is expected to act on both ratios, R/P and Rm/Rp. By comparing the ratios P/(P+Rp) (the apparent efficiency of production) and Rp/P (the apparent metabolic cost of production) in different types of organisms, one finds that a value of P/(P+Rp) = 0.75, equal to 75% efficiency, 10 mgdbm/mmol ATP, and 16 mumolO2/mg dbm (when I mg identical to 22 J), can be used as a 'consensus value' for the average efficiency, or cost, of the transformation of metabolizable energy into production in a wide range of organisms, from bacteria to mammals. This value corresponds to about three times the theoretical cost of synthesizing the same amount of tissue on the basis of known biochemical principles. The reasons why the empirical costs of production are higher than the theoretical costs of synthesis by what appears to be a common factor may be quite different in bacteria, small ectothermic and large endothermic organisms. Deviations from the consensus value may be due to differences in energy density of the nutrients assimilated and the tissues synthesized. Further complications arise because of interactions between P, Rp, and Rm. In microorganisms the existence of a constant and a variable component of maintenance metabolism has been postulated, the latter decreasing with increasing rate of production. In small ectothermic metazoans, on the other hand, the nonlinear relationship between growth metabolism and growth rate has led to the speculation that above a critical value of Pg certain energy consuming functions of maintenance are suppressed and the energy thus gained used for fuelling growth processes. There is some evidence that, at least in ectothermic metazoans, the apparent cost of growth decreases with the rate of growth, reaching a low plateau of about 10 mumolO2/mgdbm at growth rates exceeding about 8 mgdbm/g/h.(ABSTRACT TRUNCATED AT 400 WORDS)

Scaling of metabolism inHelix aspersasnails: changes through ontogeny and response to selection for increased size

“…The new research challenges the traditional conviction that 2/3 or 3/4 size-scalings are the norm, a view still dominating currently developed theories in ecology (Brown et al, 2004), and raises the question of the mechanisms explaining this diversity (Glazier, 2005;Chown et al, 2007). Our results favor the view that some part of this variability can be linked to variable growth rates, but we stress that this concept in its original form (sensu Wieser, 1994;Riisgård, 1998) overlooks the potential metabolic consequences of cellular processes associated with growth rate changes. Most organisms increase body size mainly through cell proliferation (hyperplasia) during early postembryonic development and thus with relatively little change in average cell size, but later in life mainly by cell growth and/or hypertrophy (Falconer et al, 1978;Atchley et al, 2000;Glazier, 2005).…”

“…Given that in fast-growing organisms the expenditure for biosynthesis and tissue deposition increases, and that the growth rate changes proportionally to body size, total metabolism is predicted to scale isometrically or almost isometrically with body mass in fast growers, and negatively allometrically in slow growers (Wieser, 1994;Riisgård, 1998). Reviving Bertalanffy's idea (von Bertalanffy, 1957), Glazier (Glazier, 2005) used this concept to distinguish four major types of intraspecific metabolic scaling, and he argued that much of the variability of metabolic scaling between organisms (individuals, species and higher taxa) can be explained by the effects of evolution of differential growth rates.…”

Population dynamics and metabolism of Aequipecten opercularis (L.) from the western English Channel (Roscoff, France)

“…Sibly and Calow, 1986;Wieser, 1994). The changing pattern of individual energy expenditure during the 6-y lifespan of A. opercularis clearly illustrates (i) an increasing share of maintenance requirements (expressed as respiration) in the absorbed energy (Fig.…”

Climate induced temperature effects on growth performance, fecundity and recruitment in marine fish: developing a hypothesis for cause and effect relationships in Atlantic cod (Gadus morhua) and common eelpout (Zoarces viviparus)

“…This conclusion is corroborated by the finding of a decreasing fecundity in Northern populations of cod and eelpout. Energy allocations to growth and reproduction are only possible after the requirements for physiological and biochemical homeostasis (maintenance) have been met (Wieser, 1994) including the cost of swimming and food consumption (Boutilier, 1998). The question arises which energy consuming processes are elevated in the cold and lead to decreased energy availability to growth and reproduction.…”