Environmental Hypoxia is a Driver of Sonic Hedgehog-dependent Troglomorphic Evolution in Astyanax Cavefish

Astyanax mexicanus cavefish (CF) have evolved numerous troglomorphic traits since their divergence from surface fish (SF) ancestors about 20,000 years ago. A large number of these are under the control Sonic Hedgehog (Shh), a signaling morphogen that is overexpressed along midline in CF relative to SF embryos. The Shh-dependent include eye degeneration and increases olfactory lobes, hypothalamus, jaws, oral taste buds. Eye tastebud enhancement antagonistic tradeoffs governed by pleiotropic shh gene. also multiple changes circulatory system development, highlighted larger hematopoietic domains, more erythrocytes, reversals normal heart asymmetry, which controlled Shh signaling. Although an important factor troglomorphism, gene not associated with any many QTL identified genetic analysis, suggesting upstream processes, rather than mutation locus itself, may be regulation. Due absence primary productivity, cave pools harboring deficient dissolved oxygen. Accordingly, Hypoxia Inducing Factor (HIF) transcription factors downstream targets constitutively active during development. To determine if oxygen deficiency regulator signaling, we subjected early embryos 8 or 16 hours hypoxia laboratory assayed effects on expression, erythrocyte formation, results indicated can cause overexpression, increase erythropoiesis, reverse induce We conclude environmental responsible for evolution through hyperactivation pathway.