Wednesday, March 01, 2006
Modularity and sense organs in the blind cavefish, Astyanax mexicanus.
Evol Dev. 2006 Jan-Feb;8(1):94-100.
Mexican tetra (Astyanax mexicanus) exist as two morphs: a sighted (surface) form and a blind (cavefish) form. In the cavefish, some modules are lost, such as the eye and pigment modules, whereas others are expanded, such as the taste bud and cranial neuromast modules. We suggest that modularity can be viewed as being nested in a manner similar to Bauplane so that modules express unique sets of genes, cells, and processes. In terms of evolution, we conclude that natural selection can act on any of these hierarchical levels within modules or on all the sensory modules as a whole. We discuss interactions within and between modules with reference to the blind cavefish from both genetic and developmental perspectives. The cavefish represents an illuminating example of module interaction, uncoupling of modules, and module expansion.I'm also interested in two other papers by Brian Hall. I only have the citations though:
Hall, B.K. (1984). Developmental mechanisms underlying the formationJohn Latter
of atavisms. Biol. Rev. Camb. Philos. Soc. 59, 89-124.
12. Hall, B.K. (1995). Atavisms and atavistic mutations. Nat. Genet.
(guess who's learned to use blockquotes!)
UPDATE: Reprints of Modularity and sense organs in the blind cavefish can be requested from Tamara Franz-Odentaal at the email address here
Monday, February 27, 2006
Journal of Natural History, Volume 33, Number 6, 1 June 1999, pp. 791-798(8)
In the cyclopean mutant of the anostracan branchiopod Artemia franciscana, paired stalked eyes are replaced by a single, median, sessile, eye resembling that found in certain monocular branchiopod orders. This eye, its nerve supply, and skeletal support, comprise a perfect unit which appears to be a spontaneous atavism. However, according to recent calculations this cannot be so. These suggest that while re-activation of long-silent genes, on which atavisms depend, can occur after a lapse of up to 6 million years (My), this is impossible after 10 My unless the gene is maintained by active selection, which cannot apply here. However, the Anostraca is an old group, and the atavism (if such it be) is clearly very ancient. Efficient DNA repair, not considered in the calculations, offers a possible explanation of how silent genes may survive for longer than the suggested period of viability. Particularly intriguing is that a binocular condition is primitive and the cyclopean derived, which has remarkable evolutionary implications. It suggests two reversals during the history of the Anostraca from paired sessile eyes to a long-extinct monocular condition such as prevails in certain other branchiopods, later to paired stalked eyes. Other ancient atavisms also challenge the claim that silent genes have short life spans. This problem, which has fundamental biological implications, is still sub-judice. [Evolution, shrimp]