Glassfrog embryos know when they’ve been abandoned. Luckily, they’re flexible, adapting well to the vagaries of parental care. Glassfrog males should stick around to keep their eggs moist, but if they're deadbeat dads, the embryos deal by hatching early to avoid drying out.
They might seem helpless and vulnerable, but embryos of many animals are capable of defending themselves. Sometimes they stay in the safety of their yolky eggs longer, sometimes they hatch early to escape imminent danger.
To see how parental care factors in, Jesse Delia from East Carolina University and his colleagues removed male Fleischmann's glassfrogs (Hyalinobatrachium fleischmanni) from wild populations near San Gabriel Mixtepec in Oaxaca, Mexico, during the rainy seasons of 2009 and 2010.
Glassfrog eggs rely on their dads to keep them hydrated while they’re developing. The female lays the eggs on the underside of leaves, which shield the egg clutches from rainfall, and then the males brood them. After absorbing water from a wet spot, the male will slowly release it over his clutch for about half an hour. Sometimes he’ll have to make half a dozen trips in a row. He waters each of his multiple clutches every night for up to 27 days after the eggs are laid. That takes time away from mating. But if another female does show up, then he’s off courting and getting busy for the next few days. "During that time, all the other clutches get neglected," Delia tells Science.
To see what happens with delinquent dads, the team removed 40 males from their egg clutches between 2 and 8 days after the eggs were laid, and then examined the hatchlings’ response. Unfortunately, removing the males 2 days after the eggs were laid was fatal to the embryos. But if they had at least 3 days of paternal care before they were abandoned, the embryos simply hatched early -- wiggling out of their egg capsules 12 days after they were laid. The early hatching is likely a response to deteriorating conditions without the fathers; those clutches were noticeably thinner, a sign of dehydration.
By comparison, the 50 males in the unmanipulated (control) population naturally stopped brooding their clutches between 3 and 19 days after the eggs were laid. In these cases, where the fathers stayed around and continued to care for them, the embryos extended their development in the egg.
Paternal care, they found, didn’t affect developmental rate. The abandoned embryos didn’t develop faster, they just hatched at a less mature stage. They were smaller, with simpler guts, and they also munched on the egg yolk for nutrients after they hatched. Then they'd just grow continuously and steadily.
This study is the first to document embryos escaping from bad parenting, Delia tells Science News. Being flexible and able to change behavior accordingly is called “hatching plasticity,” and it comes in handy. After all, “some are just bad dads,” he adds.
The work was published in Proceedings of the Royal Society B this week.
Images: Ruth Percino Daniel (top, middle) & Shawn Mallan, Esteban Alzate, Sean Michael Rovito (photo strip) via CalPhotos CC BY-NC-SA 3.0