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First published online January 30, 2009
Journal of Experimental Biology 212, 566-575 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026518
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Frequency information in the vibration-cued escape hatching of red-eyed treefrogs

Michael S. Caldwell1,*, J. Gregory McDaniel2 and Karen M. Warkentin1,3

1 Department of Biology, Boston University, Boston, MA 02215, USA
2 Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA
3 Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Panama


Figure 1
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  		Fig. 1. Methods for recording vibrations within egg clutches of Agalychnis callidryas. (A) Hatching-competent egg clutch with embedded accelerometer. (B) Clutches were either (left) mounted on a rigid support by taping their leaf to a plastic card, then taping the card to a jar of water or brick or (right) collected on a larger plant cutting that was maintained in a jar of water. Accelerometer and wire are colored black, duct tape and PlasticineTM mounting materials are grey.

 

Figure 2
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  		Fig. 2. Frequency spectra for eight common vibrational disturbances to Agalychnis callidryas egg clutches. Data are mean spectra and 95% confidence intervals calculated across individual spectra standardized to peak power. Dominant frequencies (means ± s.d.) and sample sizes are listed for each type of disturbance. Egg predators include the snakes (A) Leptophis ahaetulla, (B) Leptodeira annulata, (C) Leptodeira septentrionalis and (D) Imantodes inornatus and (E) the wasp Polybia rejecta. Benign disturbances include (F) wind, (G) routine embryo movements and (H) rain. Note that both embryo movements and rain are plotted over broader frequency ranges than are the other disturbances. Vibrations were recorded using accelerometers embedded in hatching-competent egg clutches. Predator attacks induced substantial hatching; benign disturbances induced little or no hatching.

 

Figure 3
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  		Fig. 3. Absolute frequency spectra for eight common vibrational disturbances to Agalychnis callidryas egg clutches, showing amplitude variation across predator and benign-source vibrations. Values are plotted on a quadratic scale in arbitrary units. Rain and wind sampled were of above-average intensity but were within the range commonly experienced by A. callidryas embryos. Note that, across all frequencies, hard rain excites higher intensity vibrations than do all other common types of vibrational disturbance. Included are 95% confidence intervals around the spectra for rain and for one typical predator class (the snake Leptophis ahaetulla).

 

Figure 4
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  		Fig. 4. Escape hatching response of Agalychnis callidryas embryos to vibration playbacks varying in frequency between 0 and 1000 Hz. Data are mean proportion hatched + s.e.m. Stimuli were 1-s bursts of 250 Hz-wide bands of noise, separated by 1-s periods of silence, played for 5 min to 5-day-old embryos. Embryos hatched in response to the lowest frequency range and showed little response to frequencies above 250 Hz.

 

Figure 5
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  		Fig. 5. Escape hatching response of Agalychnis callidryas embryos to variation in vibration frequency in the 0–250 Hz range that elicits hatching in broadband playbacks. Data are mean proportion hatched + s.e.m. Stimuli were 10 Hz-wide bands of noise, in a temporal pattern of 1-s noise:1-s silence, repeated for 5 min. Playbacks used two different shaker types, as indicated. All stimuli but one were delivered directly to clutches mounted on an immobile substrate via vibrating tines inserted among eggs. The lowest frequency stimulus (0–10 Hz) was also played to clutches mounted on a vibrating substrate. Embryos hatch more strongly in response to lower frequencies and in response to direct stimulation rather than stimulation transferred from the substrate.

 

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© The Company of Biologists Ltd 2009