“In animal life there are certain moments where what happens at that moment, could be more important than you would think…hatching is one of those moments.”
- Dr. Karen Warkentin
While trudging through the dense, soggy brush of some neotropical realm, one might come face-to-face with a translucent and gelatinous globule of tree frog eggs. Peering into the individual egg sacs fastened firmly to a leaf may reveal the distinct characteristics of life; a head, maybe even a tail. The most discerning eye might observe— through the transparent skin of this yet to be born animal—a beating, red heart. The slight movements being made throughout the habitat cause the leaves to tremble. 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, many have interpreted this experience as such. Dr. Karen Warkentin on the other hand, thought differently, leading her form the hypothesis of predator-induced escape-hatching, and embarked on a decades long journey to test it.
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 the organisms are extremely vulnerable to predation, they can receive information about the world around them and – during some developmental period – make the decision to hatch.
Phenomena so subtle as these can go unnoticed, the ferocious and loud wilderness of this planet often drowning out the nearly noiseless drop of a tiny tadpole into its aquatic home. Even more so, how perceptive of an eye would it take to capture the writhing 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 the adolescent and adult lives of the species. Understanding how the life patterns of these organisms are shaped is highly informed by the “critical transition point” of frog embryos making the decision to hatch. Taking a critical view of the many different elements of Warkentin’s research we can begin to ask further questions about the abilities of these organisms and how they might relate to our place within The Animal Kingdom. One such question might be whether these embryos are making a decision to hatch based on something inherent or something external.
The ‘will’ of an organism to survive has been described as an inherent ability, the survival mechanism a function able to be switched on and off in response to environmental pressures. Amidst this concept remains the fact of mortality, the physiological inevitability of death. Given this boundary organisms are armed with (r)evolutionarily designed tools to increase opportunities and chances for survival. Which tools to use and when to use them can be considered variable from one individual to the next, an individual's decision or in simpler terms an individual’s own will.
If there is to be an understanding of, whether the ability to make a critical decision to survive is inherent or acquired, at what point in the development of an organism does this will or ability to choose a survival mechanism arise? Further, is the choosing simply a physiological and behavioral response to environmental stimuli or rather a sentient device that actively makes personal decisions to modify the onset of death. Consider the concept of adaptive plasticity in Agalychnis callidryas, the red-eyed treefrog.
Like the red-eyed treefrog, glassfrogs lay their eggs terrestrially, on land. While studying the behavioral similarities between these species of frog can give scientist key insight into their evolutionary histories, finding a frog that is nearly transparent in a densely covered rainforest can be quite the challenge. Join Field Biologist Javier Mendez as he leads us into the realm of the elusive glassfrog.
A. Terrestrial vs. Aquatic Colonization
Lineages of frogs that evolved the ability to lay eggs on land as opposed to in water, also had to evolve mechanisms to deal with the differences in biotic and abiotic components found in these environments. How can comparing glassfrogs and their behaviors give us further knowledge of plastic hatching?
B. Glassfrog Dads
In the world of glassfrogs, it is common for the male to provide most of the parental care to their eggs. How they do so while fending off the various threats posed by the environment is an example of an evolutionary behavior that went on to alter the fate of a species.
C. Parental and Offspring Success
“Waste disposal is an issue that life faces,” explains Dr. Warkentin, and in many animals waste disposal is aided by water in its ability to flush out toxic substances which makes waste disposal much easier for aquatic animals. So how do terrestrial animals who have far less access to water cope with the issue? One answer is to let parents take care of it, but how can frog embryo’s be sure that they will be given this life saving tender love and care?