Big or fast: two strategies in the developmental control
of body size
H. Frederik Nijhout
- Correspondence:
H. F Nijhout hfn@duke.edu
Department of Biology, Duke University, Durham 27708, NC,
USA
BMC Biology 2015, 13:57 doi:10.1186/s12915-015-0173-x
The electronic
version of this article is the complete one and can be found online at VER MAS :http://www.biomedcentral.com/1741-7007/13/57
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Published:
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4 August 2015
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© 2015 Nijhout.
Open Access This article is distributed under the terms of
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Adult body size is controlled by the mechanisms that stop
growth when a species-characteristic size has been reached. The mechanisms by
which size is sensed and by which this information is transduced to the growth
regulating system are beginning to be understood in a few species of insects.
Two rather different strategies for control have been discovered; one favors
large body size and the other favors rapid development.
Age and size at maturity are arguably the two most important
life history traits of animals. Variation in both traits has severe effects on
fitness: age at maturity affects generation time and size at maturity has a
strong effect on reproductive capacity. Accordingly, age and size at maturity
have been intensively studied from an evolutionary and ecological perspective [1], [2].
Yet in spite of their obvious importance, the genetic, developmental and
physiological mechanisms that control age and size at maturity are for the most
part unknown. Nutrition and hormones play obvious and well-established roles in
growth, but the natural mechanisms that cause the cessation of growth when an
animal reaches a species-specific size remain among the great puzzles in
biology.
The recent paper by Hatem et al. [3] has shed new
light on the developmental and physiological mechanisms that regulate growth
and body size, and at the same time revealed the cause of a puzzling and
troublesome difference in mechanism between the two species, Manduca
sexta andDrosophila melanogaster, in which the control of size
has been best studied.
Growing to a species-specific size requires a mechanism that
can monitor size, and a response mechanism that stops growth and that is
triggered when a particular size is reached. Such size-monitoring and response
mechanisms are not known in any mammal, but they are now beginning to be
well-understood in several insects, specifically M. sexta, a moth,
and D. melanogaster, a fly. The proximate trigger for the cessation
of growth in insects is well-known, namely a pulse of the steroid hormone
ecdysone that occurs at the end of larval life. This pulse causes the animal to
stop feeding and begin the metamorphic molt. Insects do not grow as adults, so
the size of the larva at the time of this ecdysone pulse fully determines the
size of the adult insect.
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