Sunday, February 05, 2006


Re: [evomech] The control of body size in insects (Dev Biol)

No doubt a lot of details are being learned about ontogeny
and its regulation, but something's lacking in the general
concept, namely, what it is that is being regulated. What's being regulated
is the expression of a primordial form, a form that has many
parts, any of which may or may not be expressed. A form that's the
basis for an arthropod, or a vertebrate, or some other segmented
animal. Only something like this fits with those complex and
characteristic types emerging gradually in development, yet
suddenly in the fossil record. The basic forms are real,
yet archetypal, and their origins as trains of identical segments
were rapid processes of duplication. In a context where all
changes are reductions and distortions, the progenitor is
an archetype, underlying and explaining anatomy.


----- Original Message -----
From: "John Latter" <>
To: <>
Sent: Sunday, February 05, 2006 12:27 AM
Subject: [evomech] The control of body size in insects (Dev Biol)

[Nijhout, Developmental Biology, Sept '03]


Control mechanisms that regulate body size and tissue size have
beensought at both the cellular and organismal level. Cell-level
studieshave revealed much about the control of cell growth and
cell division,and how these processes are regulated by nutrition.
Insulin signalingis the key mediator between nutrition and the growth of
internalorgans, such as imaginal disks, and is required for the
normalproportional growth of the body and its various parts.
Theinsulin-related peptides of insects do not appear to control
growth by themselves, but act in conjunction with other hormones and
signaling molecules, such as ecdysone and IDGFs. Size regulation
cannot be understood solely on the basis of the mechanisms that control
cell size and cell number. Size regulation requires mechanisms that
gather information on a scale appropriate to the tissue or organ
being regulated. A new model mechanism, using autocrine signaling,
is outlined by which tissue and organ size regulation can be
achieved. Body size regulation likewise requires a mechanism that
integrates information at an appropriate scale. In insects, this
mechanism operates by controlling the secretion of ecdysone, which
is the signalthat terminates the growth phase of development. The
mechanisms for size assessment and the pathways by which they trigger
ecdysone secretion are diverse and can be complex. The ways in
which these higher-level regulatory mechanisms interact with cell- and
molecular-level mechanisms are beginning to be elucidated.

Full text at:

For Nijhout's latest paper (Jan '06) - see:

and a '98 paper:


Model of an Internal Evolutionary Mechanism

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