Biology Reference
In-Depth Information
It is thus of great interest to note that while smoltification and
silvering share many similarities in term of morphological, physiological
and behavioral changes, the endocrinology of these two secondary
metamorphoses drastically differs, with the major involvement of different
neuroendocrine axes, the thyrotropic/somatotropic ones for smoltifi cation
and the gonadotropic one for silvering. This suggests that secondary
metamorphoses may have been acquired independently, via different
endocrine mechanisms, during teleost evolution. The convergence between
some morphological (skin silvering, eye size and pigments), metabolic and
behavioural (downstream migration) changes refl ects that the control of the
same peripheral target organs (skin, eye, muscle, brain…) and target genes
is exerted by different hormonal receptors (thyroid hormone receptors in
salmon versus androgen receptors in the eel). This discovery suggests an
independent recruitment of different endocrine axes for the induction of
secondary metamorphoses during teleost evolution.
Most of the data available on the endocrinology of fi sh metamorphoses
concern peripheral hormones. Future studies should aim at investigating
the pituitary and brain components of the neuroendocrine axes, as well
as the mechanisms of cerebral integration of internal and environmental
factors responsible for the timing of the metamorphoses and ecophases
during the life cycles.
Acknowledgements
We thank Jérémy Pasquier (Research Unit BOREA MNHN) for his help in
the design of fi gures.
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