The Sweet Escape

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Work funded by Karen M. Warkentin and done in collabortion with KMW, Julie Jung, Ana M. Ospina, and Rachel Snyder.

Also find the poster, presented by me at the 2019 ESEB conference in Turku Finland here

It’s not only Gwen Stephani that sings about a Sweet Escape. . . turns out that the natural world is full of pretty ferocious predators that have evolved a myriad of adaptations to rip, tear, dismember, and sneak up on their unsuspecting prey. But predation isn’t a one way street– prey have developed some evasion tactics of their own. . .

But you already knew that. Crabs have shells, gazelles use evasive darting tactics, and stick-bugs use morphological camouflage to look like. . . well. . . sticks! But did you know that there are embryos, meaning individuals that haven’t even hatched from their egg capsules yet, use information from the outside world to that trigger escape hatching responses?

That’s right, and we see this in red-eyed treefrogs– imagine a snake sneaking up a tree branch where an unsuspecting clutch (which has no parent to protect it, as there is no parental care in the species) hangs over a nearby pool. Well, instead of just laying around and becoming fresh snake food, embryos cue on both tactile and motion modalities to inform premature escape hatching. Read more about our findings in our abstract and conference poster below! (with hopeful full-length paper coming out in 2020 🙂 )

ABSTRACT— When defense is more costly, prey should differentiate more strongly between predator cues and benign stimuli and may therefore use more sources of information. Red-eyed treefrog (Agalychnis callidryas) embryos hatch prematurely to escape from egg-eating snakes and wasps, cued by physical disturbance in attacks. Missing predator cues is always costly, but false alarm costs decrease with development. We assessed developmental changes in how embryos use and combine information from two sensory modalities, using a playback system to present motion (shaking), tactile contact (rubbing), or both cue types to eggs in custom-made trays at two ages. Younger embryos showed a stronger hatching response to bimodal over unimodal cues. This synergistic effect disappeared in older embryos, which responded equally strongly to unimodal and bimodal cues and had a shorter latency to hatch. This indicates younger embryos – facing higher predation risk as tadpoles – use more information for their hatching decisions. We also investigated changes in response to tactile cues (simulated wasp attack) manually applied directly to embryos through the capsule (higher threat) or on the capsule away from embryo (lower threat). Younger embryos hatched faster in response to direct tactile contact than capsule-only contact, whereas older embryos responded equally to both. Both within and across sensory modalities, developmental changes in embryos’ cue use are consistent with ontogenetic adaptation, based on improved survival chances outside the egg. Embryo hatching timing can be crucial for survival, and the cognitive processes underlying their behavioral responses have likely been shaped by developmentally changing selection pressures.

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