“They would gently poke and pinch and then physically push her off the eggs, and it would take all that to get most moms to leave,” Warkentin says. “Each embryo is surrounded by this protective layer of jelly, so when the katydid bites, it’s getting mouthfuls of jelly, and it generally gives up,” says Warkentin.īravo Valencia and Delia also tested what it would take to get glassfrog mothers to abandon their posts in the first few crucial hours. Offering these swollen egg packages to katydids, crickets that prey on frog eggs, the biologists saw some frustrated predators. The jelly surrounding the eggs then would swell up with water and grow about four times thicker. The key to this survival was that the frogs were soaking up water from damp spots on leaves and delivering it to the eggs. Monitoring the eggs daily until they hatched, which could take almost 20 days, the researchers found that the eggs given maternal care survived significantly better than those that did not receive care. Plucking out the frogs in this brief time period often required the researchers to jog up and down the stream, “so we were soaking wet all night,” Delia says. The biologists began by removing glassfrog mothers immediately after the eggs were fertilized, before the mothers could sit on the eggs. In addition to observing the 40 species of frogs through the night, Delia and Bravo Valencia performed experiments on two species of frogs in Panama. Although maternal care lasts for only one night, it helps the embryos survive. “Streams in the Andes are really steep, with impassable waterfalls every so often, and in many sites they are cascades of freezing cold water.” Egg brooding by a female Cochranella granulosa on the Rio Frijoles in Panama. “In Colombia, we would take buses…into the mountains and try to find somebody who would put us up, somewhere close to a forest, a couple hours’ hike into the stream,” says Delia, corresponding author on the study. Some of these streams were in warm lowland forests and others up in the Andes mountains. The project also included field monitoring of parental behavior throughout the duration of embryonic development for 13 species-a total of 18 months walking up and down streams every night. Delia and Bravo Valencia pursued their project over six rainy seasons at 22 sites along streams in Colombia, Ecuador, Mexico, Panama, and Peru. These discoveries were based on “a tour de force of extreme fieldwork,” says Warkentin, senior author on the paper. “Parental care gets elaborate when males take over,” Warkentin says. The research, funded by the Smithsonian Tropical Research Institute, the Fulbright Scholar Program, and the National Science Foundation, and published in the Journal of Evolutionary Biology on March 31, 2017, found, to the scientists’ surprise, parental care in every glassfrog species that they sampled.Īdditionally, in an analysis of glassfrog evolutionary history that takes advantage of the new field data, the investigators discovered that male parental care probably evolved from female care.
The two scientists found that in many species, glassfrog mothers brood their eggs during the night the eggs are fertilized, and that this care improves the survival of the eggs, while in almost a third of species, glassfrog fathers stay on guard for much longer periods. Walking along a stream in Panama very late one night, however, Jesse Delia (GRS’18) spotted a glassfrog mother sitting on her clutch of eggs.ĭelia, a PhD student in the lab of Karen Warkentin, a Boston University professor of biology, went on to observe nighttime parental behavior among no fewer than 40 species of glassfrogs, working with research partner Laura Bravo Valencia, a graduate student at the Universidad de los Andes in Bogotá, Colombia. In just a few species, fathers were known to care for their developing embryos, and biologists thought this paternal devotion had evolved from ancestors entirely lacking parental care. Until recently, biologists thought the eggs of most species were on their own during this vulnerable stage, without any help from mom or dad.
Glassfrog eggs, laid on leaves hanging over streams in tropical rainforests, are tasty snacks for snakes, insects, and other predators until they hatch and drop into the streams to begin life as tadpoles.
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