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

Ocular degeneration in the mole rat (Spalax ehrenberghi) has been offset by the hypertrophying of structures for photoperiodic sensing. The atrophied visual system and lack of reaction to light led most researchers to think that Spalax, which lives underground, is utterly sightless. However, experimental injection of tracers into Spalax retinal ganglion cells showed that some structures, such as the bed nucleus of the stria terminalis, are more highly developed than in other rodents. This development allows Spalax to control thermoregulation and other photoperiodic responses.