Why are cave-dwelling fish blind?

[Darwin_s_Finch]

@Ronald C. Semone

[quote=Triskadecamus
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Has anyone ever raised multiple generation of “cave fish” in normal light environments, and observed the nature of their development?

Tris

Or more to the point, has anyone ever raised generations of sighted fish in a totally dark environment and monitored their development?
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Developmental studies have been done on both sighted and non-sighted versions of Astyanax. Note that development in light for sightless or the dark for sighted will not really reveal much, beyond the fact that eye loss in Astyanax is an adaptation (i.e., it is not merely the developmental result of loss of light triggers; it is “programmed” at the genetic level).

As wevets notes, the jury is still out on a definitive cause. However, the 2005 study that I linked demonstrates that midline signalling genes (specifically, pax6, pax2 and hedgehog) can act as protagonists during development, and that all act on the developing eye in some fashion. If one signal is increased, eye development is altered dramatically. It does remain to be demonstrated conclusively which of the other adaptations I mentioned (and which are mentioned in the linked study) are affected by the same triggers; as the author notes:

The specific cavefish trait(s) that is positively regulated by Hh signaling and antagonistic to eye development is currently unknown. However, constructive features related to changes in cavefish feeding structures and behavior (Figure 2) are excellent candidates for such traits. In other vertebrates, shh is expressed in developing teeth (Gritli-Linde et al. 2002), in tastebuds (Hall et al. 1999, 2003), and in craniofacial structures (Helms et al. 1997), all of which are enhanced or modified in cavefish (Jeffery 2001). In preliminary studies, my colleagues and I have shown that shh expression is both sufficient and necessary for Astyanax tastebud development (Yamamoto and Jeffery unpublished data).

However, as also noted, hypoetheses based on energy conservation and neutral mutations are not supported by the current research.