Quantitative steps in the evolution of metabolic organisation as specified by the Dynamic Energy Budget theory
Kooijman, S.A.L.M. and Troost, T. A. 2007.
Quantitative steps in the evolution of metabolic organisation as specified by the Dynamic Energy Budget theory.
Biol. Rev. 82: 1 - 30
Abstract
The Dynamic Energy Budget (DEB) theory quantifies the metabolic
organisation of organisms on the basis of mechanistically inspired
assumptions. We here sketch a scenario for how its various
modules, such as maintenance, storage dynamics, development,
differentiation and life stages could have evolved since the
beginning of life. We argue that the combination of homeostasis
and maintenance induced the development of reserves and that
subsequent increases in the maintenance costs came with increases
of the reserve capacity. Life evolved from a multiple reserves -
single structure system (prokaryotes, many protoctists) to systems
with multiple reserves and two structures (plants) or single
reserve and single structure (animals). This had profound
consequences for the possible effects of temperature on rates. We
present an alternative explanation for what became known as the
down-regulation of maintenance at high growth rates in
microorganisms; the density of the limiting reserve increases with
the growth rate, and reserves do not require maintenance while
structure-specific maintenance costs are independent of the growth
rate. This is also the mechanism behind the variation of the
respiration rate with body size among species. The DEB theory
specifies reserve dynamics on the basis of the requirements of
weak homeostasis and partitionability. We here present a new and
simple mechanism for this dynamics which accounts for the
rejection of mobilised reserve by busy maintenance/growth
machinery. This module, like quite a few other modules of DEB
theory, uses the theory of Synthesising Units; we review recent
progress in this field. The plasticity of membranes that evolved
in early eukaryotes is a major step forward in metabolic
evolution; we discuss quantitative aspects of the efficiency of
phagocytosis relative to the excretion of digestive enzymes to
illustrate its importance. Some processes of adaptation and gene
expression can be understood in terms of allocation linked to the
relative workload of metabolic modules in (unicellular)
prokaryotes and organs in (multicellular) eukaryotes. We argue
that the evolution of demand systems can only be understood in the
light of that of supply systems. We illustrate some important
points with data from the literature.
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