Physiological and biochemical properties and population studies in the M lactate dehydrogenase polymorphism of Discoglossus pictus (Amphibia, Anura).

1. M LDH polymorphism has been previously described in Discoglossus pictus. 2. Gene frequency at the LdM locus varied significantly in two isolated areas which differed markedly in water oxygen tension. 3. Sex distribution, relative activity of the LDH isozymes, percentage of total H and M subunits and enzyme kinetics did not differ among the distinct LDH phenotypes. 4. Under decreasing oxygen conditions, mean time to death, LT50 and oxygen consumption were similar in tadpoles of the three LDH phenotypes (fast, intermediate and slow). 5. Our results are compatible with a neutral role for this LDH polymorphism.