Warkentin Lab Research

The Warkentin Lab – Research

Adaptive plasticity in hatching and metamorphosis:
ecology, evolution, & mechanisms

How do embryos assess danger?
The role of vibrational cues

The hatching response to egg predators depends on physical disturbance of eggs. To understand the vibrational information available to eggs, we record and analyze vibrations in egg clutches under attack, and in benign disturbances. To learn how features of vibrations affect embryo behavior, we play vibrational stimuli to egg clutches.

Dangerous and benign disturbances overlap in both frequency and temporal pattern elements. However, they can be distinguished using a combination of features. Embryos use at least two temporal pattern elements, the duration and spacing of vibration events, as well as a frequency cue, the presence of frequencies within a certain low range, to assess risk. These components are all necessary for a vibrational cue to induce hatching. Additional features of vibrations appear to further modulate the escape hatching response.

Many animals use vibrations to communicate, and to gather information about their environment. For more information on the study of vibrational signals and sensitivity, see web pages of participants in the SICB Symposium on Vibration as a Communication Channel.

• SEE A VIDEO and matching vibration recording of embryos hatching to escape from an egg-eating snake (smaller video)

Evolution of hatching plasticity in neotropical leaf-breeding treefrogs

Red-eyed treefrogs, Agalychnis callidryas (left), and gliding leaf frogs, A. spurrelli (right), differ dramatically in the response of embryos to attacks by egg-eating snakes. Red-eyed treefrog embryos hatch rapidly, up to 30% prematurely, whereas gliding leaf frog embryos show little response and are eaten. We are studying the evolution of hatching plasticity, combining phylogenetic analysis of Agalychnis and related species with experimental tests of spontaneous hatching patterns and embryo responses to risk . We are also examining the quantitative genetics of hatching-related traits in red-eyed treefrogs, using our breeding colony of this species at Boston University.

Developmental, physiological & life history plasticity: the role of oxygen stress in hatching timing

Like many amphibians, fish, and invertebrates, red-eyed treefrogs hatch prematurely if the embryos are oxygen stressed. They also show great developmental plasticity in the timing of external gill resorption: in nature, gills are maintained throughout embryonic development, but lost rapidly after hatching, even early hatching. TOP: 7 d old embryo. MIDDLE: newly hatched tadpole. BOTTOM: the same animal 3 min post-hatching. Note the reduction in gill size and perfusion.

We study connections between respiratory physiology, embryo behavior, hatching timing, and developmental plasticity. Despite their aerial incubation site, the inside of Agalychnis callidryas eggs can be strongly hypoxic. Embryo behavior may be crucially important to maintaining rapid develpment in this sparse and highly patchy oxygen environment.

• Responses of embryos to pathogens & predators: research in other laboratories

• Warkentin Lab Homepage • Biology Department, Boston University

The Warkentin Lab – Research Adaptive plasticity in hatching and metamorphosis: ecology, evolution, & mechanisms
RED-EYED TREEFROGS: Our current research with Agalychnis focuses on mechanisms, evolution, and ecological consequences of adaptive plasticity in life history switch points, particularly hatching. We are examining how hatching timing is cued by risks in the red-eyed treefrog, A. callidryas. We are studying related species, including some that differ in the response of embryos to risk, to understand how elements that contribute to hatching plasticity have evolved. We are also studying the cumulative effects of plasticity across egg, larval and metamorph stages to understand how fear and death combine to affect natural selection and population ecology. Background natural history & photo gallery of red-eyed treefrog eggs and tadpoles
How do embryos assess danger? The role of vibrational cues The hatching response to egg predators depends on physical disturbance of eggs. To understand the vibrational information available to eggs, we record and analyze vibrations in egg clutches under attack, and in benign disturbances. To learn how features of vibrations affect embryo behavior, we play vibrational stimuli to egg clutches. Dangerous and benign disturbances overlap in both frequency and temporal pattern elements. However, they can be distinguished using a combination of features. Embryos use at least two temporal pattern elements, the duration and spacing of vibration events, as well as a frequency cue, the presence of frequencies within a certain low range, to assess risk. These components are all necessary for a vibrational cue to induce hatching. Additional features of vibrations appear to further modulate the escape hatching response. Many animals use vibrations to communicate, and to gather information about their environment. For more information on the study of vibrational signals and sensitivity, see web pages of participants in the SICB Symposium on Vibration as a Communication Channel. • SEE A VIDEO and matching vibration recording of embryos hatching to escape from an egg-eating snake (smaller video)		Above: Parrot snake, Leptophis ahaetulla Below: Playback stimuli -- RED: Vibrations recorded from egg mass attacked by parrot snake; BLUE: Vibrations recorded from egg mass in rain. Stimuli are matched for duration and average amplitude. The snake playback induces hatching but the rain playback does not.

Evolution of hatching plasticity in neotropical leaf-breeding treefrogs Red-eyed treefrogs, Agalychnis callidryas (left), and gliding leaf frogs, A. spurrelli (right), differ dramatically in the response of embryos to attacks by egg-eating snakes. Red-eyed treefrog embryos hatch rapidly, up to 30% prematurely, whereas gliding leaf frog embryos show little response and are eaten. We are studying the evolution of hatching plasticity, combining phylogenetic analysis of Agalychnis and related species with experimental tests of spontaneous hatching patterns and embryo responses to risk . We are also examining the quantitative genetics of hatching-related traits in red-eyed treefrogs, using our breeding colony of this species at Boston University.

Fear, death, and life history switch points: cumulative effects of predation and predator-induced plasticity across a complex life cycle We recently discovered that not only is hatching risk-sensitve in red-eyed treefrogs, but so is metamorphosis. Like many amphibians, Agalychnis callidryas metamorphoses early in response to larval-stage risk (water bug to right). It is, however, the first species demonstrated to delay metamorphosis in response to post-metamorphic risks, specifically fishing spiders that prey on emerging metamorphs (below). We are studying how direct predation and induced responses at egg, larval, and metamorph stages interact to affect cumulative natural selection on plasticity at each stage, and the demographic importance of plastic responses.

		Developmental, physiological & life history plasticity: the role of oxygen stress in hatching timing Like many amphibians, fish, and invertebrates, red-eyed treefrogs hatch prematurely if the embryos are oxygen stressed. They also show great developmental plasticity in the timing of external gill resorption: in nature, gills are maintained throughout embryonic development, but lost rapidly after hatching, even early hatching. TOP: 7 d old embryo. MIDDLE: newly hatched tadpole. BOTTOM: the same animal 3 min post-hatching. Note the reduction in gill size and perfusion. We study connections between respiratory physiology, embryo behavior, hatching timing, and developmental plasticity. Despite their aerial incubation site, the inside of Agalychnis callidryas eggs can be strongly hypoxic. Embryo behavior may be crucially important to maintaining rapid develpment in this sparse and highly patchy oxygen environment.

Behavioral ecology of foraging in egg predators Eggs are an important resource for a variety of predators. Because near-term eggs can hatch to escape, predators might prefer young, unhatchable eggs. We studied egg foraging behavior in swarm-founding social wasps, Polybia rejecta. In fact, wasps prefered to forage on older eggs, despite their high escape rate, probably because they were easy to break into and yielded a cohesive, easy to carry prey. Thus a parental defense, the initially thick egg jelly, combines with an embryo defense, premature hatching, to focus mortality on intermediate developmental stages. In some ponds wasps attack half the egg clutches laid, so their foraging preferences might impose selection on oviposition site choice by the frogs. Moreover, developmental changes in embryo and clutch structure may affect foraging behavior in other egg-eating species.

Interacting effects of abiotic and biotic risks across three life stages in the 'pantless' treefrog
The hourglass or 'pantless' treefrog Hyla ebraccata normally lays eggs on vegetation over water, where its eggs are preyed on by ants and wasps, and require regular rainfall to avoid desiccation. In heavy rains, ponds can rise to submerge eggs, exposing them to egg-eating fishes and tadpoles. Both embryonic and larval development vary depending on environmental context. Changing rainfall patterns may be altering selection on oviposition site choice, and leading to reproductive mode variation. See J. Touchon's page for more.

	Egg ecology and defenses in vernal pool amphibians We have been studying hatching plasticity in three local (MA) amphibians, American toads (left), wood frogs and spotted salamanders. The toad eggs are frequently infected by pathogenic water molds (oomycetes), wood frogs are rarely infected and, at our study sites north of Boston, spotted salamander clutches seem never to be infected. All three species show accelerated hatching in response to mold, with toads hatching over 30% early, as soon as hatching glands develop but before they are capable of muscular movement. These precocious hatchlings appear to develop normally in the water, and may later return to feed on the water mold hyphae growing on their clutch.
• Responses of embryos to pathogens & predators: research in other laboratories
• Warkentin Lab Homepage • Biology Department, Boston University