There is a poison dart frog in South America whose skin can secrete highly toxic substances. People found that after living in an aquarium for a period of time, they are no longer toxic, and so are their offspring. Feeds on tropical ants, and no such insects breed in aquariums. Can we know from this? ['Poison arrow frog toxicity may be caused by food.', 'Poison dart frog is most toxic in tropical rain forest animals.', 'Poison dart frog heredity.', 'When visiting the aquarium, it is better to be careful with poison dart frogs.']