Karen Warkentin

Karen Warkentin
Boston University | BU · Department of Biology

PhD

About

114
Publications
17,054
Reads
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3,289
Citations
Introduction
My research examines the intersections of ecology, evolution, behavior, and physiology with development. I am particularly interested in hatching as a critical transition point where rapidly changing animals move between very different selective environments, and have also applied this perspective to metamorphosis. More broadly, I study phenotypic plasticity, early life stages, the integrative organismal biology of amphibians, and predator-prey interactions. I ground my studies in field observations of animals in their natural environment and then develop methods (e.g. for vibration playbacks) to address the questions arising from those observations. Much of my work is Neotropical, based at the Smithsonian Tropical Research Institute in Panama.
Additional affiliations
September 2001 - present
Boston University
Position
  • Professor (Associate)
June 1998 - present
Smithsonian Tropical Research Institute
Position
  • Research Associate

Publications

Publications (114)
Article
Full-text available
Climate change is increasing both environmental temperatures and droughts. Many ectotherms respond behaviorally to heat, thereby avoiding damage from extreme temperatures. Within species, thermal tolerance varies with factors such as hydration as well as ontogenetic stage. Many tropical anurans lay terrestrial eggs, relying on environmental moistur...
Article
In oviparous species, the timing of hatching is a crucial decision, but for developing embryos, assessing cues that indicate the optimal time to hatch is challenging. In species with pre-hatching parental care, parents can assess environmental conditions and induce their offspring to hatch. We provide the first documentation of parental hatching re...
Article
Full-text available
Stereotyped signals can be a fast, effective means of communicating danger, but animals assessing predation risk must often use more variable incidental cues. Red eyed-treefrog, Agalychnis callidryas, embryos hatch prematurely to escape from egg predators, cued by vibrations in attacks, but benign rain generates vibrations with overlapping properti...
Article
Full-text available
Vertebrate colonization of land has occurred multiple times, including over 50 origins of terrestrial eggs in frogs. Some environmental factors and phenotypic responses that facilitated these transitions are known, but responses to water constraints and risk of ammonia toxicity during early development are poorly understood. We tested if ammonia ac...
Article
Full-text available
As animals develop, their capacities to sense cues, assess threats, and perform actions change, as do the relative costs and benefits that underlie behavioural decisions. We presented ambiguous cues to test if hatching decisions of red-eyed treefrogs, Agalychnis callidryas, change developmentally following adaptive predictions based on changing cos...
Chapter
Full-text available
How biologists and other humans understand life has been shaped by our social history and mammalian biology, which inform the questions we ask. Compared with other tetrapods, amphibians and reptiles show amazing diversity in reproductive biology and life history. Herpetology reveals this variation, expanding what we know as possible and enabling us...
Article
Full-text available
Mechanosensory-cued hatching (MCH) is widespread, diverse, and improves survival in many animals. From flatworms and insects to frogs and turtles, embryos use mechanosensory cues and signals to inform hatching timing, yet mechanisms mediating mechanosensing in ovo are largely unknown. The arboreal embryos of red-eyed treefrogs, Agalychnis callidrya...
Preprint
Mechanosensory-cued hatching (MCH) is widespread, diverse, and improves survival in many animals. From flatworms and insects to frogs and turtles, embryos use mechanosensory cues and signals to inform hatching timing, yet mechanisms mediating mechanosensing in ovo are largely unknown. The arboreal embryos of red-eyed treefrogs, Agalychnis callidrya...
Article
Full-text available
Many animals improve offspring survival through parental care. Research on coevolution between parents has provided key insight into the genesis and maintenance of biparental care. However, understanding family dynamics more broadly requires assessing potential male–female coevolutionary processes in the more widespread and common context of unipar...
Poster
Full-text available
Climate change is increasing environmental temperatures and droughts around the world. Many tropical anurans lay terrestrial eggs, relying on environmental moisture for embryonic development. These eggs are vulnerable to dehydration, which may alter development or cause mortality. However, in some species, embryos can hatch prematurely to escape fr...
Poster
Full-text available
When defense is more costly, prey should differentiate more strongly between predator cues and benign stimuli and may therefore use more sources of information. Red-eyed treefrog (Agalychnis callidryas) embryos hatch prematurely to escape from egg-eating snakes and wasps, cued by physical disturbance in attacks. Missing predator cues is always cost...
Preprint
Full-text available
The widespread ability to alter hatching timing in response to environmental cues can serve as a defense against threats to eggs. Arboreal embryos of red-eyed treefrogs, Agalychnis callidryas , hatch up to 30% prematurely to escape predation. This escape-hatching response is cued by physical disturbance of eggs during attacks, including vibrations...
Article
Full-text available
As animals develop, their abilities and needs change, altering cost/benefit trade-offs and optimal behavior responses to cues. We tested if ontogenetic changes in information use and environmentally cued hatching decisions of embryos match adaptive predictions, using red-eyed treefrogs, Agalychnis callidryas. These arboreal embryos hatch rapidly an...
Article
Full-text available
The optimal time to hatch can vary, favouring embryos that maintain the ability to hatch or remain in ovo across a broad developmental period. Terrestrial embryos of Agalychnis callidryas hatch spontaneously at 6–7 days, but leave flooded (hypoxic) eggs as young as 3 days and escape egg predators from 4 days. We investigated the hatching mechanisms...
Article
Full-text available
Phenotypic plasticity in hatching age has been documented in many animals. A growing body of research indicates that embryos can rapidly hatch to escape egg-stage risk. However, fewer studies have tested whether selective tradeoffs in post-hatching stages favor trait plasticity. We assessed hatching plasticity and its benefits to the larval stage i...
Article
Full-text available
Hatching timing is under strong selection and environmentally cued in many species. Embryos use multiple sensory modalities to inform hatching timing and many have spontaneous hatching patterns adaptively synchronized to natural cycles. Embryos can also adaptively shift their hatching timing in response to environmental cues indicating immediate th...
Article
Full-text available
Predators can directly or indirectly shape food webs through a combination of consumptive and non‐consumptive effects. Yet, how these effects vary across natural populations and their consequences for adjacent ecosystems remains poorly resolved. We examined links between terrestrial predators and aquatic ecosystems through their effects on a locall...
Preprint
Full-text available
Hatching timing is under strong selection and environmentally cued in many species. Embryos use multiple sensory modalities to inform hatching timing and many have spontaneous hatching patterns adaptively synchronized to natural cycles. Embryos can also adaptively shift their hatching timing in response to environmental cues indicating immediate th...
Preprint
Hatching timing is under strong selection and environmentally cued in many species. Embryos use multiple sensory modalities to inform hatching timing and many have spontaneous hatching patterns adaptively synchronized to natural cycles. Embryos can also adaptively shift their hatching timing in response to environmental cues indicating immediate th...
Article
Full-text available
Terrestrial eggs have evolved repeatedly in tropical anurans exposing embryos to the new threat of dehydration. Red-eyed treefrogs, Agalychnis callidryas, lay eggs on plants over water. Maternally provided water allows shaded eggs in humid sites to develop to hatching without rainfall, but unshaded eggs and those in less humid sites can die from de...
Article
Full-text available
Hatching is an essential and often behaviourally mediated process. Many animals can hatch at different developmental stages, and embryos time hatching based on cues indicating threats to eggs or opportunities outside them. However, specific mechanisms enabling such responses, and how their ontogenies combine to determine when environmentally cued h...
Article
Many animals provide parental care to offspring. Parental sex-roles vary extensively across taxa, and such patterns are considered well documented. However, information on amphibians is lacking relative to other vertebrate groups. We combine natural history observations with functional and historical analyses to examine the evolution of egg care in...
Poster
Full-text available
Hatching early allows embryos to escape threats to eggs, but increases risks to larvae. Red-eyed treefrogs hatch by rapidly releasing enzymes to digest a small hole in their membrane, then squeezing out aided by turgor pressure. Displacement from the initial hole can occur spontaneously and in predator attacks, complicating hatching by capsular col...
Article
Full-text available
Environmentally cued hatching allows embryos to escape dangers and exploit new opportunities. Such adaptive responses require a flexibly regulated hatching mechanism sufficiently fast to meet relevant challenges. Anurans show widespread, diverse cued hatching responses, but their described hatching mechanisms are slow, and regulation of timing is u...
Article
Compensatory growth is well documented across taxa and provides a fitness advantage to animals who would otherwise reach a smaller reproductive size. We investigated the role of competition-induced gut plasticity in facilitating a compensatory response in red-eyed treefrog larvae. We reared larvae at low, medium, and high densities with different p...
Article
Life history theory predicts that organisms with complex life cycles should transition between life stages when the ratio of growth rate (g) to risk of mortality (l) in the current stage falls below that in the subsequent stage. Empirical support for this idea has been mixed. Implicit in both theory and empirical work is that the risk of mortality...
Article
Theory predicts that prey behavioural responses should reflect the level of risk posed by predators. We investigated how red-eyed treefrog embryos perceive and respond to spatially variable risk during wasp attacks on their clutches. First, we spatially restricted wasp activity on clutches and compared hatching of wasp-exposed, adjacent, and protec...
Article
Full-text available
To adaptively express inducible defenses, prey must gauge risk based on indirect cues of predation. However, the information contained in indirect cues that enable prey to fine-tune their phenotypes to variation in risk is still unclear. In aquatic systems, research has focused on cue concentration as the key variable driving threat-sensitive respo...
Article
For animals with complex life cycles, conditions in the larval environment can have important effects that persist after metamorphosis. These carryover effects may influence juvenile growth plasticity and have important fitness consequences.Small juvenile red-eyed treefrogs, Agalychnis callidryas, grow faster than larger ones. We examined to what e...
Article
Most animals have complex life histories, composed of a series of ecologically distinct stages, and the transitions between stages are often plastic. Anurans are models for research on complex life cycles. Many species exhibit plastic timing of and size at metamorphosis, due to both environmental constraints on larval growth and development and ada...
Conference Paper
Background/Question/Methods Theory predicts that organisms with complex life cycles should minimize the ratio of growth rate (g) to risk of mortality (µ) when transitioning between life stages. However, the majority of studies have found no effect of predators on timing of or size at metamorphosis. Two things may contribute to this discrepancy. F...
Article
Full-text available
Most animals metamorphose, changing morphology, physiology, behavior and ecological interactions. Size- and habitat-dependent mortality risk is thought to affect the evolution and plastic expression of metamorphic timing, and high predation during the morphological transition is posited as a critical selective force shaping complex life cycles. Non...
Article
Plasticity in the timing of transitions between stages of complex life cycles allows organisms to adjust their growth and development to local environmental conditions. Genetic variation in such plasticity is common, but the evolution of context-dependent transition timing may be constrained by information reliability, lag-time and developmental co...
Article
Full-text available
Environmentally cued plasticity in hatching timing is widespread in animals. As with later life-history switch points, plasticity in hatching timing may have carryover effects that affect subsequent interactions with predators and competitors. Moreover, the strength of such effects of hatching plasticity may be context dependent. We used red-eyed t...
Article
Full-text available
In animals with complex life cycles, fitness trade-offs across life stages determine the optimal time for transitions between stages. If these trade-offs vary predictably, adaptive plasticity in the timing of life history transitions may evolve. For instance, embryos of many species are capable of accelerating hatching to escape from egg predation...
Article
Full-text available
Community ecology aims to understand how species interactions shape species diversity and abundance. Although less studied than predatory or competitive interactions, facilitative interactions can be important in communities associated with ephemeral microhabitats. Successful recruitment from these habitats requires species to rapidly colonize, dev...
Article
Full-text available
To effectively balance investment in predator defenses versus other traits, organisms must accurately assess predation risk. Chemical cues caused by predation events are indicators of risk for prey in a wide variety of systems, but the relationship between how prey perceive risk in relation to the amount of prey consumed by predators is poorly unde...
Conference Paper
Background/Question/Methods The ability of predators to alter the size structure of prey populations via consumption is well documented and can have important consequences for population and community dynamics. Predators can also alter prey size via non-consumptive mechanisms. Prey often experience reduced growth in response to indirect cues of r...
Article
Full-text available
Spatial contagion occurs when the perceived suitability of neighbouring habitat patches is not independent. As a result, organisms may colonize less-preferred patches near preferred patches and avoid preferred patches near non-preferred patches. Spatial contagion may thus alter colonization dynamics as well as the type and frequency of post-coloniz...
Conference Paper
Metamorphosis dramatically changes morphology, physiology, behavior and performance. As anurans change from aquatic tadpoles to terrestrial juveniles, they pass through a period of poor locomotor performance and high predation risk, and individuals behaviorally determine when they shift habitats. Red-eyed treefrogs, Agalychnis callidryas, alter whe...
Conference Paper
Background/Question/Methods The nonlethal effects of predators on prey phenotype and performance can propagate through foodwebs to affect the outcome of predator-prey interactions (trait mediated interactions; TMIs). To produce effective defensive phenotypes requires environmental cues that indicate both presence of predators and the level of ris...
Conference Paper
Background/Question/Methods Organisms often exhibit strong habitat preferences, but the relative importance of habitat preference for predicting species’ distributions can be strongly dependent upon the spatial configuration of patches in the landscape. Patch clustering can lead to increased colonization of both preferred and non-preferred patche...
Article
Many species of frogs and salamanders, in at least 12 families, alter their timing of hatching in response to conditions affecting mortality of eggs or larvae. Some terrestrially laid or stranded embryos wait to hatch until they are submerged in water. Some embryos laid above water accelerate hatching if the eggs are dehydrating; others hatch early...
Article
Most animals begin life in eggs, protected and constrained by a capsule, shell, or other barrier. As embryos develop, their needs and abilities change, altering the costs and benefits of encapsulation, and the risks and opportunities of the outside world. When the cost/benefit ratio is better outside the egg, animals should hatch. Adaptive timing o...
Article
Full-text available
The functional response is a critical link between consumer and resource dynamics, describing how a consumer's feeding rate varies with prey density. Functional response models often assume homogenous prey size and size-independent feeding rates. However, variation in prey size due to ontogeny and competition is ubiquitous, and predation rates are...
Conference Paper
The primitive dampwood termite Zootermopsis angusticollis uses vibrational communication to warn nestmates about dangers facing the colony. One mode of vibrational communication is the pathogen alarm response (PAR), in which the termite vibrates in a seizure-like manner warning nestmates of the presence of lethal conidia concentrations of the entom...
Article
1. Behavioural, morphological and coloration plasticity are common responses of prey to predation risk. Theory predicts that prey should respond to the relative magnitude of risk, rather than a single level of response to any risk level. In addition to conspecific and predator densities, prey growth and differentiation rates affect the duration of...
Conference Paper
Background/Question/Methods Most animals undergo substantial changes in body size and morphology during ontogeny. Body size determines many aspects of ecological performance, including foraging rate, fecundity, range size and predation risk. Size structure in prey populations can strongly influence predator-prey interactions, and prey size select...
Conference Paper
Background/Question/Methods Most species have complex life cycles in which they are vulnerable to different suites of predators as they shift habitats through ontogeny. While these predators, separated in time and space, do not interact directly, they may still interact indirectly via their effects on the density and traits of their shared prey. F...
Conference Paper
Background/Question/Methods As organisms with complex life cycles transition between life-stages, trade-offs in risks and opportunities focus selection from two sequential, potentially variable environments. Plasticity in the timing of life history switch points, such as hatching and metamorphosis, is phylogenetically widespread and allows organi...
Conference Paper
Background/Question/Methods The assembly of communities can be shaped pre-colonization by processes like habitat selection as well as post-colonization by processes such as species interactions. The relative importance of processes operating at these two scales for communities that inhabit ephemeral, patchy microhabitats are poorly understood and...
Conference Paper
Background/Question/Methods Many amphibians respond plastically to predator cues, changing behavior, morphology, and hatching or metamorphic timing. These responses are often predator-specific or modulated by factors indicative of the level and nature of risk. The terrestrial embryos of red-eyed treefrogs, Agalychis callidryas, hatch prematurely to...
Article
Development consists of growth and differentiation, which can be partially decoupled and can be affected by environmental factors to different extents. In amphibians, variation in the larval environment influences development and causes changes in post-metamorphic shape. We examined post-metamorphic consequences, both morphological and locomotory,...
Article
Full-text available
Sensitivity to substrate-borne vibrations is widespread in animals and evolutionarily precedes hearing but, compared with other sensory modalities, we know little about vibrational communication, particularly in vertebrates. For plant-dwelling arthropods, vibrations are likely as important as sound. Arboreal vertebrates excite plant vibrations with...
Article
1. Environmental variation during development is common and often has long-lasting effects on phenotypes and survival. In organisms with complex life cycles, such effects may carry over from one life stage into the subsequent stages, affecting reproductive success and survival in both direct and indirect manners. Much research has focused on the tr...
Article
Full-text available
Many organisms show adaptive phenotypic plasticity in response to environmental variation. Some environmental factors may, however, impose constraints on the ability of organisms to respond to other factors. The neotropical treefrog Dendropsophus ebraccatus lays eggs both above water on leaves and directly in water, thereby exposing embryos to diff...