It all starts when Mom lays eggs on the forest floor. Dad fertilizes them and watches over them as they develop. Once they hatch, he squats next to each tadpole as it squirms up his leg and onto his back, taking each one on a piggyback ride to their own tiny puddle of water. He’ll search for just the right spot, often depositing them at the heart of leafy bromeliads, where tightly overlapping leaves — think of a pineapple — collect and pool rainwater.
Dad has to ensure that his babies are separated, because these tadpoles are cannibals. “They’re highly aggressive,” says Lauren O’Connell, a biologist and Goolsby’s Ph.D. adviser at Stanford University. “They have a very small water pool, not a lot of resources, and they will defend this area to the death.”
The skin-to-skin contact with dad during the piggyback ride also transfers important microbes to the tadpole. “Basically, it’s a way to seed their tadpoles with a microbiome,” O’Connell says. “It changes a lot about how they look and the kind of microbes that they have.”
Once Dad has found a home for each of his tadpoles, he starts making the rounds. He’ll travel from tadpole to tadpole every day, ensuring that his babies are hydrated and checking on their growth. Tadpoles recognize their parents by smell, and their brains will light up with dopamine when they sense Dad nearby. If they’re hungry, they’ll start wiggling around to beg for food like a puppy enthusiastically wagging its tail. But Dad can’t feed them on his own, so he’ll stay by their side and call to Mom incessantly with a high-pitched trilling sound until she arrives.
“He sings for her to come and provide an egg meal,” Goolsby says.
When Mom sees the tadpole begging, she’ll dive into the pool and produce an unfertilized egg for it to eat, “like a protein shake basically,” O’Connell says. “Mom comes, and the tadpole basically has to dance for their food.”
Mom is making a huge investment in each tadpole by feeding it her unfertilized eggs instead of using those to produce more babies, but the tadpoles are far more likely to survive because of it. Being cared for by their parents until they can morph into frogs supercharges their growth, and these eggy “protein shakes” help them reach metamorphosis much faster. The quicker they can grow legs and move about on their own, the safer they are from predators, such as fishing spiders, who seek out vulnerable tadpoles for a quick meal.
Fortunately for the tadpoles, their parents leave them with a defense against prey. As the tadpoles munch on the eggs, they’re getting more than just nourishment — these are poison frogs, after all, and each egg is loaded with alkaloids that make the tadpoles toxic to eat.
“And so not only are they giving them nutrition, they’re chemically defending them,” O’Connell says, “and so they’re less likely to get eaten.”
After several weeks of careful parenting, the tadpoles emerge from their pools as froglets. The dedication and teamwork of these frog parents is essential: In studies where the dads were removed, tadpole survival declined by 70%.
“To have your offspring survive,” says Summers, “it becomes really important to have the participation of both the mother and father.”
These frogs are toxic, but they’re called mimic poison frogs because they imitate the look of other poison frogs living nearby. In a clever disguise, they take on the swirling or striped patterns of three different species, all brilliantly colored in vibrant hues of green, orange, yellow and blue. This helps predators in an area learn to avoid them all — and it’s an effective strategy.
During her fieldwork in the tropics, O’Connell has asked local community members which animals they’ve seen eating poison frogs. She says their response is always a resounding, “Oh, I’ve never seen anything eat those frogs.” Whereas nontoxic frogs offer opportunistic predators like birds and snakes a tasty snack, and only 20% make it to the next year, “poison frogs can live for 14 years,” says O’Connell.
In fact, poison frogs are some of the most toxic animals in the world. They don’t actually produce their own poison, but get it from their diet of ants and mites, absorbing toxic alkaloids and concentrating them in glands under their skin. They can have around 50 different toxins, but the “cocktail” can change throughout their lives based on shifts in their diet. Special proteins bind up the toxins to protect their own nervous systems from the poison, “like toxin sponges,” says O’Connell.
The researchers think one of the reasons the mimic poison frogs evolved to have such intensive parental care is their limited resources. The pools of water where the tadpoles grow up are so small that they’d have no food if Mom didn’t provide eggs for them to eat. And Dad’s role is extra important because of how much work it is for Mom to produce eggs. With the tadpoles in day care with Dad, Mom can spend her time eating and looking for food.
“I think it’s really interesting that there’s this one ecological factor that may drive monogamy in these frogs — the pool-size factor, which really kind of focuses attention on the importance of biparental care,” says Summers.
According to Summers, parental care like this isn’t just critical for survival — it’s also linked to better outcomes for the frogs when they become adults. “Biparental care allows for childhood, and childhood allows for the evolution of a bigger brain and more sophisticated intellectual abilities. Basically, you have the time to become a better adult,” he says.
Goolsby agrees that these frogs can offer up lessons about successful parenting that apply across species — even for people.
“This species is so fascinating because there’s no models on how parents work as a team,” she says. “That’s a very understudied component of biparental care, but it’s core to so many care strategies.”
Goolsby spends hours watching frog couples care for their young for her research, and she sees some distinct parallels between these nurturing amphibians and human families.
“What’s interesting is that they’re like new parents. So you know, when they’re trying to raise their first babies and then the male loses the tadpole or can’t get it right when he’s trying to hydrate them and guard them — it’s like trying with your first child. And it’s very difficult.”
But like any dedicated father, she says, he keeps trying.
