Will to Survive

While wading through a densely forested pond in some Neotropical realm, one might come face-to-face with a translucent and gelatinous globule of treefrog eggs. Peering into the individual egg sacs fastened to a leaf and hanging above the water may reveal the distinct characteristics of life: a head, a tail, perhaps a movement. The most discerning eye might observe—through the transparent skin of this yet to be born animal—a beating, red heart. Leaves tremble from even the slightest maneuvers through the habitat. The tiny beings in their pods start to quake as well, and plop! Those who were unborn just a moment ago are now swimming in the water below. Was it a coincidence that these embryos hatched so quickly? Certainly, some have interpreted similar observations as such. Karen Warkentin, on the other hand, thought differently – leading her to form the hypothesis of predator-induced escape-hatching and embark on a decades-long journey studying embryo behavior.

In Warkentin’s very first paper on the subject she described how these pre-natal beings have the ability to make evaluative decisions in response to environmental conditions in order to stay alive. Warkentin explains that, while eggs are extremely vulnerable to predation, the embryos inside them can receive information about the world around, and – during some developmental period – make the decision to hatch.

Phenomena subtle as these can go unnoticed in the jungle. The competing chorus of tropical birds and insects often drowns out the nearly noiseless drop of a tadpole into its aquatic home. Even more so, how perceptive one would have to be in order to capture the stirrings of these minuscule creatures hesitant in their egg capsule waiting for the right moment to hatch – or not. Warkentin’s research embarks on the journey of red-eyed treefrogs from conception to hatching and into their adolescent and adult lives. Understanding how the life patterns of these organisms are shaped is informed by a “critical transition point,” as Warkentin describes, when embryos make the decision to hatch.

Taking a broader view of the many elements of Warkentin’s research, we can begin to gauge the further implications behind the abilities of these organisms. The Narrow Escapes that treefrog embryos make from their predators happen too often to be called a coincidence, but how are they distinguishing external threats— like a parrot snake attacking a clutch— from something as harmless as rainfall. Despite being faced with these terrestrial dangers, somewhere along the organisms’ evolutionary history, the species was able to leave an aquatic habitat and colonize land. At the River Frijolito we can gain insight into the challenges of making such a transition, by observing the habits of another lineage of terrestrial egg layers, the glassfrog.

Perhaps both the aforementioned phenomena can be clarified by observing these embryos under a microscope. When layer upon layer of body tissue is examined it is revealed that certain physiological mechanisms are triggered in the embryo in response to external cues. These Microscopic Revelations suggest that the interaction between embryos and the outside world may be happening at a neurological level, even more complex than previously believed. Perhaps it is with this possibility that we can begin to question what it means for an organism to inherit the will to survive. Consider the concept of adaptive plasticity in Agalychnis callidryas, the red-eyed treefrog.