What the egg can tell about its hen: Embryonic development on the basis of dynamic energy budgets |
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Authors: | S A L M Kooijman |
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Institution: | (1) Department of Theoretical Biology, Vrije Universiteit, de Boelelaan 1087, 1081 HV Amsterdam, The Netherlands |
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Abstract: | The energy cost of offspring is important in the conversion of resources allocated to reproduction to numbers of offspring,
and in obtaining energy budget parameters from quantities that are easy to measure. An efficient numerical procedure is presented
to obtain this cost for eggs and foetusses in the context of the dynamic energy budget theory, which specifies that birth
occurs when maturity exceeds a threshold value and maternal effects determine the reserve density at birth. This paper extends
previous work to arbitrary values of the ratio of the maturity and somatic maintenance costs. I discuss the body size scaling
implications for the relative size and age at birth and conclude that the size at birth, contrary to the age at birth, covaries
with the maintenance ratio. Apart from evolutionary adaptation of the maturity at birth, this covariation might explain some
of the observed scatter in the relative length at birth. The theory can be used to evaluate the effects of the separation
of cells in e.g. the two-cell stage of embryonic development, and of the removal of initial egg mass. If cell separation hardly
affects energy parameters, body size scaling relationships imply that cell separation can only occur successfully in species
with sufficiently large maximum body length (as adult); i.e. some two times that of Daphnia magna. Toxic compounds that increase the cost of synthesis of structure, decrease the allocation to reproduction indirectly via
the life cycle, because food uptake is linked to size. They can also decrease the egg size, however, such that the reproduction
rate is stimulated at low concentrations. The present theory offers a possible explanation for this well-known phenomenon.
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Keywords: | Dynamic energy budget theory Embryonic development Cost of an egg Foetus Incubation time Length at birth Body size scaling relationships Removal of reserve Hormesis |
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