Conference Paper
Pleiotropic tradeoffs between constructive and regressive traits during troglomorphic evolution
Jeffery, W.R.
Record Number:
4737
Year:
2010
Editor:
Moskric, A. and Trontelj, P.
Abstract:
The adaptive benefits of regressive troglomorphic
traits, such as eye and pigment degeneration, are difficult to identify in
cave animals. We have approached this problem by studying the
developmental and molecular relationships between several different
constructive and regressive traits. In the cavefish Astyanax mexicanus,
sonic hedgehog (shh) overexpression along the embryonic midline is
responsible for eye degeneration. Subsequently, shh overexpression
spreads to the cavefish oral-pharyngeal area. Cavefish have constructive
oral-pharyngeal traits, including larger mouths and more taste buds,
relative to surface dwelling Astyanax. A tradeoff between constructive
oral pharyngeal development and optic degeneration has been
demonstrated by conditional shh overexpression in surface Astyanax
© Biospeologica Bibliographia
Publications 2010-1
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Bernard LEBRETON & Jean-Pierre BESSON
Créé le : 01.01.2010
Modifié le : 30.06.2010
embryos, which increases mouth and taste bud development at the
expense of eyes via pleiotropic Shh signaling. Cavefish lack melanin
synthesis in regressed pigment cells due to loss-of-function mutations in
oca2, which normally regulates the supply of L-DOPA precursor during
melanin synthesis. The block in cavefish pigmentation occurs at a
metabolic branch point in which L-tyrosine is normally converted either
(1) to L-DOPA, DOPAquinone, and melanin by tyrosinase or (2) to LDOPA,
dopamine, and related catecholamines by tyrosine hydroxylase
and other enzymes. A similar block in the initial step of melanin synthesis
has evolved independently in the cave plant hopper Oliarus polyphemus
and other diverse cave animals. In Astyanax cavefish, the benefit of lost
melanin pigment appears to be the production of excess L-DOPA and its
derivative dopamine by the second alternative pathway, which promotes
constructive development of dopaminergic neurons and enhances the
magnitude of adaptive feeding behavior. We conclude that the evolution
of beneficial constructive traits could have driven regressive traits via
developmental tradeoffs encoded in pleiotropic genes, which adapt cave
animals to life in darkness.
Times Cited:
1
Conference Name:
20th International Conference on Subterranean Biology
Conference Year:
2010
Conference Location:
2010
Conference Location:
2010
Relevent Species: