GOMEZ-MESTRE, I.*; WARKENTIN, K.M.; Boston University; Boston University: Embryo response to risk varies among species of leaf-breeding treefrogs, genus Agalychnis
Arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, hatch prematurely in response to various egg-stage risks, including attack by egg-eating snakes and wasps, infection by pathogenic fungus, and submergence underwater (risk of drowning). Early hatching is an effective defense against egg-stage risks (ca. 80% escape from snakes and wasps), but early-hatched tadpoles are more vulnerable to aquatic predators. Similar risk-cued hatching plasticity occurs in several other anuran species, as well as in salamanders, fishes, and spiders. To understand its evolution, we need comparative studies including species that are unresponsive to risk, as well as risk-sensitive species. We examined embryo responses to risk in other species of Agalychnis to assess how variable they are across the genus, as a first step toward a phylogenetic analysis of the evolution of hatching plasticity. Like A. callidryas, both A. spurrelli and A. annae showed extended hatching periods. A. annae can be induced to hatch by mechanical disturbance or submergence underwater 24-48 h before spontaneous hatching occurs, but A. spurrelli is much less responsive to the same stimuli. Embryos of A. spurrelli and A. annae are also preyed upon by egg-eating snakes. However, when exposed to snake attack within the hatching period, the escape rate of A. spurrelli embryos was less than that of A. callidryas or A. annae eggs, averaging only 15%. Most embryos that were consumed showed no attempt at escape, remaining passive during the physical disturbance of their clutch. A. spurrelli clutches submerged underwater hatch much more slowly than A. callidryas and A. annae of the same age. Like A. callidryas, A. annae suffers a trade-off between egg- and larval-stage risks. Planned work will examine hatching responses to standardized risk treatments in other Agalychnis species and frame the results in a phylogenetic context.
