Captive-bred axolotls, the salamanders with a big smile, can survive in the wildIt’s an important discovery since axolotls are now found only in Lake Xochimilco, Mexico City.Recognizable by their feathery external gills, between 50 and 1,000 of the critically endangered amphibians are left in the wild. But a study in Mexico City monitored 18 axolotls…