The development of behavioral defenses: a mechanistic analysis of vulnerability in red-eyed tree frog hatchlings |
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Authors: | Warkentin Karen M |
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Institution: | Department of Zoology, University of Texas, Austin, TX 78712,
USA |
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Abstract: | I examined the development and effectiveness of behavioral defensesof
red-eyed tree frog hatchlings, Agalychnis callidryas, against
predatoryshrimp Macrobrachium americanum. Arboreal eggs of A.
callidryashatch early if attacked by egg predators and later if
undisturbed,producing tadpoles that enter the water at different
developmentalstages. Older hatchlings survive better than young hatchlings
withaquatic predators, including shrimp. Hatchlings respond to shrimpby both
increasing activity and avoiding the bottom microhabitat.Older hatchlings are
more active and, in the presence of shrimp,avoid the bottom more than young
hatchlings. These ontogeneticchanges in behavior improve survival.
Specifically, the likelihoodof fleeing from shrimp increases with hatchling
age, and fleeingis an effective defense. In contrast to results from
experimentswith odonates, immobility does not reduce risk of shrimp attack,
thusthere is no trade-off between fleeing and motionless crypsis.Shrimp
spend most of their time on the bottom, where attacksare more often
successful. Avoidance of the bottom microhabitatby tadpoles therefore
improves survival. Evasive maneuvers alsofunction in defense, but evasiveness
does not change with age.Morphology may limit microhabitat use by younger
hatchlings.Failure to flee may reflect unresponsiveness to disturbance,which
would reduce unnecessarily early hatching and limit exposureof young A.
callidryas to aquatic predators. |
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Keywords: | activity Agalychnis defense development Macrobrachium microhabitat predation shrimp tadpoles |
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