Ocular regression conceals adaptive progression of the visual system in a blind subterranean mammal

The mole rat, is an extreme example of natural visual degeneration in mammals: visual pathways are regressed and incomplete and the absence of visual cortical potentials or an overt behavioural response to light have led to the conclusion that is completely blind But structural and molecular investigations of the atrophied, subcutaneous eye suggest a functional role for the retina in light perception and entrainment of circadian locomotor and thermoregulatory rhythms by ambient light demonstrates a capacity for photoperiodic detection We report here that severe regression of thalamic and tectal structures involved in form and motion perception is coupled to a selective hypertrophy of structures subserving photoperiodic functions. As an alternative to the prevalent view that ocular regression results from negative or nonselective evolutionary processes the differential reduction and expansion of visual structures in can be explained as an adaptive response to the underground environment.