Smaller Domiciles Force Frog Monogamy
Animals aren't well known for their monogamy. The name of the game is spreading the seed, and the more eggs you can fertilize, the better. The cost of being monogamous typically outweighs the benefits, and most non-mammalian offspring can fend for themselves straight out of the nest, so there's often not a reason for mates to stay together after copulating. Dolphins, elephants and some types of birds are known to mate monogamously, some for life, but the "lesser" species tend to follow a more polygamous route. So, who would have thought that a mere frog would be willing to spurn its lothario ways and make a cozy home with the mistress?
Deep in the rainforests of South America dwells the Peruvian poison frog (also known as the mimic poison frog), and he is the epitome of a doting husband... as long as the dwelling demands his monogamy. Dr. Jason Brown and his colleagues from East Carolina University have found that the male mimic poison frog is forced into monogamy due to the small pools of water that the tadpoles are kept in.
After the tadpoles hatch in a communal puddle, the male takes each tadpole to its own dwelling inside a small pool of water captured within a plant. These pools of water are too small to offer any real sustenance, so the female frog must come along occasionally and lay unfertilized eggs for the tadpole to eat. The female is alerted to the tadpole's hunger by the father, who keeps a close watch on his offspring. In fact, he must keep such a close eye that he is prevented from sneaking off and mating with any other available females.
The variable poison frog, a close relation to the mimic poison frog, however, engages in polyandry. Its eggs are laid in larger pools of water, usually five times larger than the pools of the mimic poison frog. The female lays the eggs and says sayonara, leaving the male to raise the brood.
When researchers upgraded tadpoles from diminutive puddle to palatable pool, the tadpoles flourished. It seems that the larger the area of water, the more nutrients available to the tadpoles - the female doesn't need to lay protein-rich eggs to keep them growing, she is free to leave and the male is free to wander. However, in a smaller pool, both the male and female frogs are necessary for the tadpole's survival.
Source: News BBC