Environmentally cued hatching occurs when embryos adaptively alter the timing of hatching in response to environmental cues. This phenomenon is quite common in frogs. My research addresses the question of how diverse frogs are able to adaptively alter the timing of hatching in response to threats, and whether different species do this in different ways.
Red-eyed treefrogs, Agalychnis callidryas
Red-eyed treefrogs can hatch rapidly to escape snake predators, with no prior degradation of the egg capsule. How do they do it? We have found that they acutely release hatching enzyme from hatching gland cells, which are densely concentrated on the snout of embryos and quickly regress after hatching.
Here is the video abstract from our recent paper in Journal of Experimental Biology:
Hourglass treefrogs, Dendropsophus ebraccatus
Hourglass treefrogs hatch early in two contexts: under acute threat of predation by ants, and in response to dehydration, a chronic threat. We are investigating how they are able to alter hatching timing in both of these contexts. We are using an integrative approach to consider how development, physiology and behavior affect hatching regulation in this species. I use scanning electron microscopy, qPCR, and video analysis to test whether differences in hatching gland cell development, hatching enzyme gene expression, and behavior contribute to differences in hatching timing.
American toads, Anaxyrus americanus
American toads are an abundant North-American species which lay their eggs in vernal pools. These eggs can become infected with water mold, and can hatch 44% early to escape, which is before they are even capable of muscular movement. I am using scanning electron microscopy to look at hatching gland cell ontogeny and qPCR to assay hatching enzyme expression to determine how hatching is regulated in this species.
Cohen KL, Piacentino ML, Warkentin KM. (2017) The hatching process and mechanisms of adaptive hatching acceleration in hourglass treefrogs. Comp Biochem Phys, Part A. In press.
Warkentin KM, Cuccaro Diaz J, Güell BA, Jung J, Kim SJ, Cohen KL. (2017) Developmental onset of escape-hatching responses in red-eyed treefrogs depend on cue type. Anim Behav 129: 103-112.
Cohen KL, Seid MA, Warkentin KM. (2016) How embryos escape from danger: the mechanism of rapid, plastic hatching in red-eyed treefrogs. J Exp Biol 219, 1875-1883. pdf: CohenEtAl2016JExpBio
Fraser, D. F., Brosseau, C., Cohen, K. L. and Morse, S. A. (2011). Guppies as heterospecific facilitators: a precursor of exploratory behavior? Behav Ecol Sociobiol 65, 1113-1122.