Subterranean Fishes of the World

3266

2017

AIM 2017

The entrance of Caballo Moro Cave (CM) is a karst window: A habitat within cave systems that are exposed to light resulting from cave ceiling collapse. The cave’s entrance pit is 4 km away from the nearest surface fish locality. The entrance pit leads to a 90m stream pool. Light only reaches half of the pool, while the other half remains in darkness. The distribution of fish is biased, with blind fish in the dark area and eyed fish in the illuminated area. What is the origin of the eyed Caballo Moro cave fish? Are they simply surface fish that swam across kilometers of underground passages or are they direct descendants of cave fish that have been selected to re-acquire eyes? Whole genome DNA-sequencing of 8 eyeless CM, 7 eyed CM and 6 surface fish, showed that the eyed CM fish are more similar to eyeless CM fish (Fst=0.137) than to surface fish (Fst=0.179). Results also showed that eyed CM retain portions of surface genome which are absent in the eyeless CM genome. Abundance of contiguous surface SNP’s on contigs were tabulated. Very few long surface genome fragments of 10 contiguous SNP’s were found (0.1%) while on the contrary small fragments of single isolated surface SNP’s abound (35.0%). This suggests an old evolutionary time of isolation from surface fish and selection for specific surface portions of the genome maintained in the standing genetic variation of Caballo Moro fish. In line with the genomic data, we found that eyed CM share a host of characters with eyeless cavefish that include: large eggs, small liver lobules, reduced pigmentation of the peritoneum, large fat deposits, suborbital bones with the signature of belonging to a cavefish that has recuperated the eyes, and VAB. Contrary to surface fish, eyed CM attack less other epigeomorphic fish (39.6% +/-36.0 stdev) and instead prefer to attack troglomorphic fish, potentially generating a reproductive behavioral barrier, promoting the possibility of long term sympatric speciation in these populations.

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