The Grindylows that inhabit the Black Lake has developed different mechanisms to survive the conditions in their environment. Through careful observation we have compiled the most likely combination of physiological adaptations for the Grindylows to thrive in their habitat. In order to survive in the conditions of the Black Lake, the Grindylow faces multiple challenges. Primarily, their living condition can be categorized into three phases; summer day, summer night and winter. During the summer days, the environment is hyperoxic(pO2>400mmHg) and hypocapnic(PCO2~0mmH) with temperatures up to 28 degrees Celsius. On the other hand, in summer nights the water becomes hypoxic(pO2~10mmHg) and hypercapnic(pCO2~25mmHg) with the same temperature. …show more content…
The proposed mechanism for dealing with these challenges is that Grindylows are osmoconformers and ionoregulators. They have reduced skin permeability to prevent water loss through epidermal osmosis into the hypertonic environment and gills/kidneys to regulate the ion concentration in the body. By reducing skin permeability, the Grindylows are unable to perform cutaneous gas exchange as a possible solution during hypoxic conditions. The water loss is compensated by ingesting sea water and excreting the excess salt and produce concentrated urine to maintain water retention. The salt excretion takes place in both the gills and the lumen of the Grindylows. A Na+/K+/2Cl- co-transporter brings Cl- and K+ into the cell using Na+ electrochemical gradient. Cl- then exits through the apical membrane via an anion channel by its electrochemical gradient, created by the Na+/K+ ATPase, into the lumen or the external water. At the same time K+ leaves through the basolateral K+ channel. The Na+ that enters the cell with K+/Cl- leaves in exchange for K+ via the Na+/K+ ATPase. As the Cl- is sent outside the cell it creates a small electrical potential between extra cellular fluid and seawater. The potential difference drives the outward movement of Na+ between the cells thus excreting the salt in the body. The glomerulus of the kidney reabsorbs macromolecules such as …show more content…
NH3 and NH4+ can passively diffuse through the cell into the water or NH4+ can be pumped into the gill by substituting for K+ at basolateral Na+/K+-ATPase then pumped out of the gill by substituting for H+ at an apical H+/Na+ exchanger. The benefit of ammonia excretion for the Grindylow is that it requires very little metabolic cost and it only requires large amount of water that is readily available around them. However, due to the increased pH during winter, the Grindylow would need to switch to urea excretion as ammonia cannot diffuse if the environmental pH is higher than ammonia's pKa of 9-9.5. Urea production is more metabolically expensive than ammonia but requires less water for excretion. Urea excretion can be done either through passive diffusion into water or creating a gradient of low Na+ in the gill and high Na+ in blood for the Na+ to diffuse into the cell through an urea transporter taking urea with it, then the urea diffuses out into the water. In addition, urea can be used as an osmolyte to prevent freezing in turns of being freeze