Review Article – Article Example
Circadian Photoreception The minds of non-mammalian vertebrates possess numerous photoreceptive cells that are essential for instituting the circadian rhythms of behavior and physiology. Such photoreceptive cells are also predicted amongst mammals being evolved from nocturnal ancestors. In order to explore the presence of these photoreceptive cells that contributes to the circadian rhythms entrainment to the light and dark cycle. So in order to explore the photoreception in a mole rat who is found to be completely blind. The blindness of Spalax was evident from the incomplete and regressed visual pathways. Also an open behavioral reaction to light and lack of visual cortical potentials validate its blindness.
However, the molecular and structural probes of the subcutaneous eye (atrophied) indicate retina performs an operational role in light perception as well as the entrainment of thermoregulatory rhythms and circadian locomotors by ambient light evidences a capability for photoperiodic detection. It has been reported that rigorous regression of tectal and thalamic structures concerned in motion and form perception is joined to an exclusive hypertrophy of structures assisting photoperiodic functions. So the study provides and imperative to link the ocular regressions (the differential expansion and reduction) found in Spalax as an outcome of adaptation to the underground environment. Since the view prevailing suggested that the ocular regression consequences from nonselective or negative evolutionary processes.
The study concludes that the photoperiodic system, maintaining appropriate thermoregulatory and reproductive responses, has been exclusively expanded, while the acute metabolic load of keeping a visible eye along with the non-operational ‘image forming sensory system renders the inherent evolutionary drift for their structural regression. Therefore, ocular regression, paired with selective advancement of photoperiodic pathways, presents a single facet of distinctive range of adaptations evolved within the subterranean mammals to meet environmental restraints enforced by the underground environment (Cooper, Herbin and Nevo 159).
The study basically provided a clue to answer the question of whether the mammals possess the photoreceptive cells that respond to the variations in light and dark cycle.
Cooper, Howard M., Herbin, Marc and Nevo, Eviatar. “Ocular regression conceals adaptive progression of the visual system in a blind subterranean mammal.” Nature 361. 6408 [14 Jan. 1993]: 156-159. Print.