It was around 4 a.m. And for Jesse Delia, a graduate student conducting fieldwork in Panama, it had been a long night. His project wasn’t going well, and he was ready to head home. On his way back from the stream where he had been working, he stopped by a spot to have another look at a mating pair of frogs he had seen earlier. It didn’t relate to his project, but he wanted to see what they were up to.

There, a female glass frog was sitting on her eggs. He tried to nudge her off, but she wouldn’t budge. This was unusual. The books said most glass frog larvae were on their own after fertilization. And for the rare cases in which larvae did receive parental care, it came from the father.

Was this for real?

After that night, Mr. Delia set aside his original project and embarked on a five-year quest with Laura Bravo Valencia, a graduate student at the Universidad de los Andes in Bogotá, Colombia.

Together, they spent rainy all-nighters along wet streams at 22 research sites across Colombia, Peru, Panama, Mexico and Ecuador to see if this parental behavior could be found elsewhere and, if so, how it evolved.