Subterranean Fishes of the World

3205

2013

AIM 2013

Using tissue transplantation, Yamamoto and Jeffery (2000) accomplished the restoration of eyes lost in the evolution of cavefish. In essence, despite a cavernicole genetic background, fish with eyes were created. A similar case appears to also be present in nature, but brought about instead by the effect of natural evolutionary forces. Caballo Moro Cave (CMC) is a karst window in which the cave system was exposed to light by ceiling collapse. The cave is 4 km away from the nearest surface fish locality. The entrance pit leads to a large pool. Light only reaches the upstream half of the pool, while the downstream half remains in darkness. The pool contains mostly blind depigmented fish in the dark area and eyed pigmented fish in the illuminated area. Results with RAPD fingerprint markers (Espinasa and Borowsky, 2000) indicate that the eyed fish may be distinct from the nearby surface population. Eyed fish of CMC appeared to be genetically closer to blind cave fish from the region, than to the surface fish. These results were confirmed with microsatellite data (Strecker et al 2012). Through experimental manipulation, Cave fish that have regained eyes undergo many bone modifications, making their skulls resemble surface fish. Nonetheless, they have a signature difference in bone distribution. While in all surface, F1 and F2 fish studied the suborbital bones extend to almost the level of the preopercular and opercular bones, in experimentally eyed cave fish the suborbital bones retain the small size of cavefish, creating a gap between the preopercular and the outer border of the suborbital. When the skulls of eyed CMC fish are examined, they had a distinctive gap and were indistinguishable from laboratory treated cavefish that had regained the eyes. Histologically the eyes of the eyes fish of CMC are similar to surface fish except for a detail: the retina has a vascularization not previously recorded either for surface fish or surface and cave hybrids. Blood vessels are seen deep within the retina, in between the ganglionic layer and the fibers of the optic nerve. In agreement with previous genetic information, the skull and eye morphology of the eyed CMC fish does not support an origin via surface fish. Instead, it would appear that blind cavefish had an evolutionary history with some sort of independent “reconstruction” that led to an eye and skull not quite identical to surface fish.

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