Biology Reference
In-Depth Information
Overall, what we observed in mammals and bird species for which data
are available is a stage of organ maturation that corresponds to a period of
autonomy acquisition by the young that is concomitant to a TH peak,
and probably a period of high sensitivity to the hormone. We propose that
this period should be considered as equivalent to Anuran metamorphosis,
and defined as a TH-controlled functional remodeling of organs allowing
the maturation of main physiological system preparing the entry into a
new ecological niche. This clearly suggests that in most vertebrates there
is a deployment of the TH signaling pathway that allows this transition. This
process is tightly coupled to the environment via the nervous system and the
connection with the internal milieu due to the roles of the HPT axis. This
explains why variations of this period, linked to variation of life history strat-
egy, occurred and this offers interesting prospects for future research in order
to explore how in some species heterochronic shifts of the TH-sensitive
period might have occurred.
To conclude, it is important to acknowledge that this new unifying
vision of postembryonic development of vertebrates is very speculative, full
of unsolved questions. It is clear that experimental data should challenge this
vision but it has the advantage of being a framework on which experimental
evidence could be confronted. We are convinced that shaking this model
will allow to shed a new light on postembryonic development in amniotes.
ACKNOWLEDGMENTS
We are very grateful to Barbara Demeneix for critical reading and many fruitful suggestions.
All errors and omissions are entirely ours. We apologize to our colleagues whose work was
not cited adequately for lack of space. Work from our laboratory is supported by the CNRS,
the Agence National de la Recherche, the French Ministry of Ecology (PNRPE), and the
European Commission.
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