Comparing risk-induced hatching across species of tropical treefrogs, genus Agalychnis.
Gomez-Mestre, Ivan*,1, Warkentin, Karen1, 2, 1 Dept. of Biology, Boston, MA, USA2 Smithsonian Tropical Research Institute, Panama City, Panama
ABSTRACT- Risk-induced hatching is a widespread embryonic response to environmental hazards, both biotic and abiotic. To understand the evolution of risk-induced hatching and its mechanism we need comparative studies including species that are unresponsive to risk, as well as risk-sensitive species. We have examined embryo responses to risk in several species of tropical treefrogs from the genus Agalychnis, as a first step toward a phylogenetic analysis of the evolution of hatching plasticity. As previously shown for A. callidryas, its congeners A. spurrelli, A. annae, A. saltator, and A. calcarifer exhibit extended hatching periods. A. callidryas, A. annae and A. spurrelli can be induced to hatch by mechanical disturbance or submergence underwater 24-48 h before spontaneous hatching occurs, and A. calcarifer can be induced up to 72h before spontaneous hatching. Embryos of all these species are naturally preyed upon by egg-eating arboreal snakes. However, when exposed to snake attack within the hatching period, the escape rate of A. spurrelli embryos (15% per clutch on average) was remarkably lower than that of A. callidryas or A. annae embryos (80%). Most A. spurrelli embryos that were consumed showed no attempt to escape, remaining passive during the physical disturbance of their clutch. Risk of drowning by submergence underwater induces similar early hatching responses in A. callidryas and A. annae. Although sensitive to this stimulus, A. spurrelli clutches submerged underwater hatch much more slowly than A. callidryas and A. annae of the same age. Current phylogenetic information on this group suggests that the sensitivity and efficacy of risk-induced hatching may have been secondarily reduced in A. spurrelli.
Key words: hatching timing, phenotypic plasticity, anti-predator behavior, comparative analysis
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