Motherly poison frogs shed light on maternal brain - Stanford Report

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For most frogs, motherhood begins and ends with the release of hundreds of eggs into a sizable body of water and then hopping or swimming away.

A Climbing Mantella tadpole with a recently laid unfertilized egg. (Image credit: Alexandre Roland)

Two curious exceptions are the Little Devil frog of Ecuador and the Climbing Mantella of Madagascar. The females of both poison frog species lay only a few eggs at a time, depositing each one into its own tiny pool formed from the cupped leaves of native rainforest plants. The mothers then spend months painstakingly feeding each tadpole unfertilized eggs until they are ready to leave their aquatic nests.

Why all the devotion? A team led by Stanford biologist Lauren O’Connell has discovered an intriguing possible answer.

In a new study published Nov. 21 in the journal Current Biology, the scientists report that the nutritious eggs the frogs feed their hatchlings are also laced with poisons, likely as a way of passing chemical defenses on to the next generation.

“This egg provisioning strategy is a way for these frogs to chemically defend their offspring sooner,” said O’Connell, who is an assistant professor of biology in the Stanford School of Humanities and Sciences.

By comparing the brains of the two frogs with each other and with mammals, the researchers also discovered new clues that have bearing on an even greater biological mystery: the neural basis of motherhood itself.

Convergent evolution

Despite their convergent reproductive strategies, the Little Devil and the Climbing Mantella are about as different as two frog species can be. They each split from a common ancestor some 140 million years ago, around the time the first amphibians appeared, and have since evolved independently on opposite ends of the globe.

This early evolutionary schism, combined with their very un-froglike nursing strategy, makes them ideal for investigating the evolution of maternal care, O’Connell said. “Maternal behavior has evolved only once in mammals,” she added. “We wanted to know, are there different ways to build the maternal brain? Or do they all use the same mechanisms and molecules? These frogs allow us to investigate these questions.”

Another reason these frogs are valuable case studies for maternal care is that only the mothers are involved in rearing the tadpoles. “Some frogs do have bi-parental care, but the neural mechanism behind that is complicated because you can’t really disentangle the relationship with the tadpole from pair-bonding between the parents,” said study co-author Nora Asher Moskowitz, a graduate student in O’Connell’s lab. “These frogs allow you to study maternal care in isolation.”



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