Strong Selection is Necessary for Evolution of Blindness in Cave Dwellers

1 Blindness has evolved repeatedly in cave-dwelling organisms, and investigating loss of sight presents an 2 opportunity to understand the operation of fundamental evolutionary processes, including drift, selection, 3 mutation, and migration. The observation of blind organisms has prompted many theories for their 4 blindness, including loss-by-disuse and selection against eye development when eyes are not used. Here 5 we have developed amodel that shows just how strong selection must be for blind populations of a cave6 dwelling species to evolve. We used approximations to determine levels of selection that would result in 7 caves containing only sighted individuals, only blind individuals, or a stable population of both. We then 8 incorporated drift into the model using simulations. Based on our model, strong selection is necessary 9 for the evolution of blindness unless immigration rates are extremely low. Drift decreased the fixation of 10 blindness in populations, although for intermediate levels ofmigration the level of selection required to fix 11 blindness decreased substantially. We hypothesize that this degree of selection may be due to phototaxis 12 in sighted individuals, whomove toward the light leaving only blind individuals in the cave. 13 1 . CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/031872 doi: bioRxiv preprint first posted online Nov. 16, 2015;