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Crocodilians have high concentration of lactic acid in their blood. This is the cause that prevents them from prolonged intense activity, since prolonged intense activity causes the muscles to secrete more and more lactic acids, up to the stage where the lactic acid level become lethal - even for the crocodile.

So the shortcomings of high level of lactic acid are clear, it restricts activity and endangers the croc to death.

So why in the first place crocodiles have high level of lactic acid? What is the advantage of this?

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  • $\begingroup$ Remember that not every evolved trait is advantageous. Some can be maladaptive, brought about by selection for another adaptive trait. $\endgroup$ – NatWH Sep 17 '18 at 15:51
  • $\begingroup$ Do you have a reference showing that lactic acid is normally high in the blood of crocodilians? Or is it simply that they can tolerate higher levels of lactic acid? The two are quite different circumstances. $\endgroup$ – Bryan Krause Sep 20 '18 at 15:28
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    $\begingroup$ en.wikipedia.org/wiki/Lactic_acidosis#Reptiles Reptiles, which rely primarily on anaerobic energy metabolism (glycolysis) for intense movements, can be particularly susceptible to lactic acidosis. In particular, during the capture of large crocodiles, the animals' use of their glycolytic muscles often alter the blood's pH to a point where they are unable to respond to stimuli or move.[19] Cases are recorded in which particularly large crocodiles which put up extreme resistance to capture later died of the resulting pH imbalance.[20] some reptiles can sleep underwater anaerobically. $\endgroup$ – com.prehensible Sep 21 '18 at 10:27
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As far as I can tell from a brief literature search, the explanation for the high concentration of lactic acid in the blood of crocadilians is two-fold:

  1. The lactic acid is generated from the anaerobic muscular activity involved in capturing their prey.

In a gloss from Science Daily a journalist writes:

Concealed below the water's surface, crocodilians stealthily approach animals that have come to drink, spring upon their prey, and drag them into the water and drown them. This powerful burst of activity generates an extraordinary amount of lactic acid in their muscles…

  1. It is maintained at a relatively high concentration in blood so it can be used to acidify the stomach for the digestion of its meal.

I am less sure about this. Certainly the crocodile needs to acidify the stomach, and the scientific article glossed by the Science Daily shows how the lungs are bypassed to allow carbon dioxide to reach the stomach:

During this period of digestion crocodilians divert blood through a special vessel that bypasses the lung, named the left aorta… …when crocodilians are digesting a meal, they chose to shunt and direct CO2-rich blood straight to the stomach where glands make use of the CO2 to form gastric acid and bicarbonate. Consequently this shunt enables crocodilians to secrete gastric acid at a rate that is approximately 10 times the highest rates measured in mammals.

My supposition is that lactic acid also contributes to the acidity, but I may be wrong on this point. If anyone has information about this, I shall be happy to add it to my answer.

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