About

Karen Warkentin is a Professor of Biology and Women’s, Gender, & Sexuality Studies at Boston University. She is a queer, gender non-conforming, white, female Canadian who grew up in small towns in Kenya and Canada, in a mixed-race Mennonite family. Her early activism as a feminist and queer advocate was shaped by her experiences as a Biology undergraduate, where she was among the few queer and female faculty members in STEM. Her research primarily focuses on Latin American herpetology, with a long-term program in Panama at the Smithsonian Tropical Research Institute and connections to Costa Rica, Colombia, and Ecuador. She is invested in mentoring and creating opportunities for young Latine herpetologists and has contributed to integrating insights from Women’s, Gender, & Sexuality Studies with her scientific work to promote inclusive biology. Warkentin has been actively involved in diversity and inclusion initiatives, co-chairing the university-wide LGBTQIA+ Faculty & Staff Task Force and serving on the CAS Diversity and Inclusion Action Team. In response to the COVID-19 pandemic and the broader social justice movements, she has prioritized antiracist work within her department and the university, aiming to foster a more inclusive environment where BIPOC students and colleagues can thrive.

Research topics

• Biology
• Ecology
• Zoology
• Cell biology
• Genetics
• Evolutionary biology
• Neuroscience
• Anatomy

Selected publications

• Effects of larval foam-making and prolonged terrestriality on morphology, nitrogen excretion and development to metamorphosis in a Leptodactylid frog

  PeerJ · 2025-02-26 · 1 citations

  articleOpen accessSenior author

  At ontogenetic transitions, animals often exhibit plastic variation in development, behavior and physiology in response to environmental conditions. Most terrestrial-breeding frogs have aquatic larval periods. Some species can extend their initial terrestrial period, as either a plastic embryonic response to balance trade-offs across environments or an enforced wait for rain that allows larvae to access aquatic habitats. Terrestrial larvae of the foam-nesting frog, Leptodactylus fragilis , can arrest development, make their own nest foam to prevent dehydration, and synthesize urea to avoid ammonia toxicity. These plastic responses enable survival during unpredictably long periods in underground nest chambers, waiting for floods to enable exit and continued development in water. However, such physiological and behavioral responses may have immediate and long-term carry-over effects across subsequent ecological and developmental transitions. We examined effects of prolonged terrestriality and larval foam-making activity on larval physiology, development, and metamorphosis in L. fragilis . We tested for changes in foam-making ability by measuring the nests larvae produced following complete removal of parental foam at different ages. We measured ammonia and urea levels in larval foam nests to assess nitrogen excretion patterns, testing for effects of larval age, soil hydration around parental nests, and repeated nest construction. We also assessed immediate and long-term effects of larval foam-making and prolonged terrestriality on larval morphology at water entry and development to metamorphosis. We found that larvae arrested development during prolonged time on land and even young larvae were able to effectively produce multiple foam nests. We found high ammonia concentrations in larval nests, very high urea excretion by developmentally arrested older larvae, and faster growth of larvae in water than while constructing nests. Nonetheless, sibling larvae had a similar aquatic larval period and size at metamorphosis, regardless of their nest-making activity and timing of water entry. Sibship size increased the size of larval foam nests, but reduced per-capita foam production and increased size at metamorphosis, suggesting maternal effects in cooperative groups. Metamorph size also decreased with aquatic larval period. Our results highlight the extent of larval ability to maintain and construct a suitable developmental environment and excrete N-waste as urea, which are both crucial for survival during enforced extensions of terrestriality. Our results suggest that the energetic reserves in large eggs are sufficient to meet metabolic costs of urea synthesis and foam production during developmental arrest over an extended period on land, with no apparent carry-over effects on fitness-relevant traits at metamorphosis.

  PublisherDOI

• Author response for "Functional Morphology of Hatching: Ontogeny and Distribution of Hatching Gland Cells in Red‐Eyed Treefrogs and a New Marker for Anuran Hatching Enzyme"

  2025-01-14

  peer-reviewSenior author
  PublisherDOI

• The Role of Vibration Amplitude in the Escape-Hatching Response of Red-Eyed Treefrog Embryos

  Integrative Organismal Biology · 2025-01-01 · 3 citations

  articleOpen accessSenior author

  Synopsis The function and adaptive significance of defensive behaviors depend on the contexts in which they naturally occur. Amplitude properties of predator cues are widely used by prey to assess predation risk, yet rarely studied in the context of the stimuli relevant to defensive decisions in nature. Red-eyed treefrog embryos, Agalychnis callidryas, hatch precociously in response to attacks on their arboreal egg clutches by snakes and wasps. They use vibrations excited during attacks to detect predators, but wind and rainstorms also excite intense vibrations. Past work has demonstrated that to avoid costly decision errors, A. callidryas nonredundantly combine information from the temporal and frequency properties of clutch vibrations. Here, we demonstrate that embryos also use absolute amplitude and fine-scale amplitude modulation information to refine their hatching decision. We used vibration recordings to characterize the amplitude properties of the most common predator and benign-source disturbances to A. callidryas egg clutches in nature and tested whether embryos at 3 ages across the onset of mechanosensory–cued hatching (4–6 days) respond to amplitude variation during playback of synthetic vibrations to eggs. Older embryos responded to much lower-amplitude vibrations, reflecting a >88-fold decrease in response threshold from 4 to 5 days. To assess how embryos combine amplitude with other vibration properties, we played embryos recorded exemplars of snake attack and rain vibrations of varying amplitudes and patterns of amplitude modulation. The amplitude response curve was steeper for snake recordings than for rain. While amplitude information alone is insufficient to discriminate predator attack from benign-source vibrations, A. callidryas employ an impressively complex strategy combining absolute amplitude, amplitude modulation, temporal, and frequency information for their hatching decision.

  PublisherDOI

• Ontogeny of the Heat‐Induced Hatching Response in the Red‐Eyed Treefrog, <i>Agalychnis callidryas</i>

  Journal of Experimental Zoology Part A Ecological and Integrative Physiology · 2025-11-29

  articleSenior author

  ABSTRACT In ectothermic vertebrates, temperature impacts the rate and success of embryonic development, and in some species, embryos show adaptive behavioral responses to thermal conditions. The arboreal embryos of red‐eyed treefrogs exhibit heat‐induced hatching, escaping to cooler water below and demonstrating a limit to their behavioral thermal tolerance, or Voluntary Thermal Maximum (VT Max ). Their escape response to warming has been studied only at developmental stages 31–34 (age 5 days), although these embryos hatch in response to other threats as early as stage 24 (age 3 days). Hence, it is unclear when heat‐induced hatching begins or how this behavior may change with further development. We conducted an ontogenetic series of warming trials to determine the onset of heat‐induced hatching, assess developmental changes in the proportion of embryos that respond, and test whether expression of VT Max changes with development. No embryo tested at stage 26 hatched; heat‐induced hatching began in some clutches at stage 27. The proportion of embryos hatched increased from 3% at stage 27 (age 4.3 days) to 86% at stage 30 (5.4 days) when all clutches were responsive. The greatest variation in response among clutches occurred at stage 29. Hatching temperature was similar across stages 27–30 (38.2 ± 1.3°C) and consistent with the VT Max reported for stage 31–34 embryos (38.1 ± 0.8°C) under similar testing conditions. These findings provide new insights into the ontogeny of heat‐induced hatching behavior and reveal that embryos can escape from heat more than a day earlier than previously shown. The ontogenetic stability of VT Max suggests a consistent thermal threshold guiding this response, providing reliable protection against lethal temperatures. This plasticity may help embryos withstand increasing thermal stress under climate change.

  PublisherDOI

• Heat-Induced Hatching: Clarifying Effects of Hydration and Heating Rate on Behavioral Thermal Tolerance of Red-Eyed Treefrog Embryos

  Integrative Organismal Biology · 2025-01-01 · 1 citations

  articleOpen accessSenior author

  Synopsis Anurans are one of the most diverse groups of vertebrates but also most threatened by current climate change effects such as increasing environmental temperatures and more frequent and prolonged periods without rain. Many tropical anurans lay terrestrial eggs that are particularly vulnerable to drying and warming. In some such species, embryos hatch prematurely to escape from drying eggs. In red-eyed treefrogs, Agalychnis callidryas, embryos hatch early to escape both drying and excessive warming, expressing a behavioral thermal tolerance (i.e., VTMax). Prior research suggested that drying reduces the VTMax of embryos. However, because hydrated clutches warmed more slowly, the effect of drying on VTMax was confounded with that of faster warming. To disentangle these dynamics, we designed a novel apparatus to warm terrestrial frog egg-clutches at controlled rates and minimize evaporative cooling. We independently manipulated clutch hydration and heat input to assess their individual and combined effects on embryo VTMax. Proportional egg-volume loss was similar across hydration × heat input categories. High heat input resulted in higher clutch warming rates and shorter trial durations, across hydration levels. Within clutches, warming rates differed between back and surface thermocouple positions, generating thermal gradients as warming progressed. Clutch dehydration reduced embryo VTMax, with no main or interacting effect of heat input. This evidence that egg drying reduces thermal tolerance across testing conditions supports a direct role for hydration in the behavioral decisions of warming embryos, rather than an indirect effect mediated by changes in evaporative cooling. It suggests that embryos assessing risk integrate information about hydration, and perhaps changes in hydration, with information about current and changing temperature. These findings highlight the value of methods to independently manipulate hydration and heating rate, showing the complexity of thermal ecology in embryonic ectotherms. We encourage further research on temperature and hydration effects on embryo hatching to better understand tropical anurans’ adaptive strategies under climate change.

  PublisherOA PDFDOI

• Functional Morphology of Hatching: Ontogeny and Distribution of Hatching Gland Cells in Red‐Eyed Treefrogs and a New Marker for Anuran Hatching Enzyme

  Journal of Morphology · 2025-01-28 · 1 citations

  articleSenior author

  Environmentally cued hatching (ECH) is widespread in animals and requires regulation of hatching mechanisms. Enzymatic digestion of the egg membrane is a common hatching mechanism in vertebrates and invertebrates. In amphibians and fishes, hatching enzymes (HE) are synthesized and released by hatching gland cells (HGC), whose functional ontogeny determines when hatching can occur. Ontogenetic studies of HGC development or HE expression are limited, based largely on external cell morphology; few markers for HGC or HE are available, and those appear specific for Xenopus. Moreover, mechanisms regulating HE release are unknown in anurans. To investigate variation in the hatching process, we need tools to identify and analyze its components. Agalychnis callidryas (Hylidae) is a well-established model of ECH, showing plastically timed, acute HE release, unlike the gradual release described for some aquatic anurans. We developed a new antibody marker for A. callidryas HE that also labels HGC/HE in glassfrogs (Centrolenidae). As glassfrogs and treefrogs diverged 62 mya, the antibody may be broadly useful in anurans. We used the AcHE antibody to examine the development and distribution of HGC and accumulation of HE, two key elements of hatching mechanisms, in A. callidryas. We found a much larger number (ca. 4200) and broader distribution of HGC than has been documented in any amphibian, with HGC densely but non-contiguously distributed over the front of the head and eyes and scattered along the dorsal midline. HE expression begins before hatching competence and is strong throughout the plastic hatching period, unlike HE gene expression which diminishes after competence. The distribution and expression ontogeny of A. callidryas' HE/HGC appear related to their hatching performance, plasticity, and embryo morphology. The AcHE antibody will enable comparative research to elucidate co-variation in the functional morphology, performance, and ecological context of hatching.

  PublisherDOI

• Sustaining socially just and accurate life sciences teaching for sex, gender, and reproduction?

  Natural sciences education · 2025-06-30 · 5 citations

  article

  Abstract For decades experts have called for improving equity in science education regarding sex, gender, and reproduction, with little large‐scale change. To identify potential approaches to change, we convened an interdisciplinary group of biologists, education researchers, and gender and science studies scholars. Our conversations revealed a fundamental need to work across multiple scales, including change within life science classes and simultaneously at larger culture and systems scales in the life sciences and society as a whole. We used the multiple‐loop learning framework to explore solutions across scales: Single‐loop learning is change within existing structures, such as addressing terminology used in teaching; double‐loop learning engages with why a problem exists, such as incorporating the history and philosophy of science into life sciences education; triple‐loop learning questions underlying assumptions, such as shifting life science's culture and norms to value interdisciplinarity; and quadruple‐loop learning involves societal‐level changes, such as working across communities and social change. We argue that cultural changes in the values and norms in the life sciences, educational institutions, and society more broadly are essential for lasting transformation.

  PublisherDOI

• Egg-Clutch Biomechanics Affect Escape-Hatching Behavior and Performance

  Integrative Organismal Biology · 2024-01-01 · 3 citations

  articleOpen accessSenior author

  Synopsis Arboreal embryos of phyllomedusine treefrogs hatch prematurely to escape snake predation, cued by vibrations in their egg clutches during attacks. However, escape success varies between species, from ∼77% in Agalychnis callidryas to just ∼9% in A. spurrelli at 1 day premature. Both species begin responding to snake attacks at similar developmental stages, when vestibular mechanosensory function begins, suggesting that sensory ability does not limit the hatching response in A. spurrelli. Agalychnis callidryas clutches are thick and gelatinous, while A. spurrelli clutches are thinner and stiffer. We hypothesized that this structural difference alters the egg motion excited by attacks. Since vibrations excited by snakes must propagate through clutches to reach embryos, we hypothesized that the species difference in attack-induced hatching may reflect effects of clutch biomechanics on the cues available to embryos. Mechanics predicts that thinner, stiffer structures have higher free vibration frequencies, greater spatial attenuation, and faster vibration damping than thicker, more flexible structures. We assessed clutch biomechanics by embedding small accelerometers in clutches of both species and recording vibrations during standardized excitation tests at two distances from the accelerometer. Analyses of recorded vibrations showed that A. spurrelli clutches have higher free vibration frequencies and greater vibration damping than A. callidryas clutches. Higher frequencies elicit less hatching in A. callidryas, and greater damping could reduce the amount of vibration embryos can perceive. To directly test if clutch structure affects escape success in snake attacks, we transplanted A. spurrelli eggs into A. callidryas clutches and compared their escape rates with untransplanted, age-matched conspecific controls. We also performed reciprocal transplantation of eggs between pairs of A. callidryas clutches as a method control. Transplanting A. spurrelli embryos into A. callidryas clutches nearly tripled their escape success (44%) compared to conspecific controls (15%), whereas transplanting A. callidryas embryos into different A. callidryas clutches only increased escape success by 10%. At hatching competence, A. callidryas eggs are no longer jelly-encapsulated, while A. spurrelli eggs retain their jelly coat. Therefore, we compared the hatching response and latency of A. spurrelli in de-jellied eggs and their control, jelly-encapsulated siblings using manual egg-jiggling to simulate predation cues. Embryos in de-jellied eggs were more likely to hatch and hatched faster than control siblings. Together, our results suggest that the properties of parentally produced egg-clutch structures, including their vibration biomechanics, constrain the information available to A. spurrelli embryos and contribute to interspecific differences in hatching responses to predator attacks.

  PublisherOA PDFDOI

• 39 LESSONS IN PATIENCE: Frog Eggs, Snakes, and Rain

  Cornell University Press eBooks · 2024-04-23

  book-chapter1st authorCorresponding
  PublisherDOI

• The role of vibration amplitude in the escape hatching response of red-eyed treefrog embryos

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-09-24

  preprintOpen accessSenior author

  Abstract The function and adaptive significance of defensive behaviors depend on the contexts in which they naturally occur. Amplitude properties of predator cues are widely used by prey to assess predation risk, yet rarely studied in the context of the stimuli relevant to defensive decisions in nature. Red-eyed treefrog embryos, Agalychnis callidryas , hatch precociously in response to attacks on their arboreal egg clutches by snakes and wasps. They use vibrations excited during attacks to detect predators, but wind and rainstorms also excite intense vibrations. Past work has demonstrated that to avoid costly decision errors, A. callidryas non-redundantly combine information from the temporal and frequency properties of clutch vibrations. Here we demonstrate that embryos also use absolute amplitude and fine-scale amplitude modulation information to refine their hatching decision. We used vibration recordings to characterize the amplitude properties of the most common predator and benign-source disturbances to A. callidryas egg clutches in nature and tested whether embryos at three ages across the onset of mechanosensory-cued hatching (4–6 days) respond to amplitude variation during playback of synthetic vibrations to eggs. Older embryos responded to much lower-amplitude vibrations, reflecting a &gt;88-fold decrease in response threshold from 4 to 5 days. To assess how embryos combine amplitude with other vibration properties, we played embryos recorded exemplars of snake attack and rain vibrations of varying amplitudes and patterns of amplitude modulation. The amplitude response curve was steeper for snake recordings than for rain. While amplitude information alone is insufficient to discriminate predator attack from benign-source vibrations, A. callidryas employ an impressively complex strategy combining absolute amplitude, amplitude modulation, temporal, and frequency information for their hatching decision.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Fear, Death, and Life History Switch Points - Cumulative Effects of Phenotypic Plasticity and Predation across Three Life Stages

  NSF · $516k · 2007–2011

• How Embryos Assess Danger: The Role of Vibrational Cues

  NSF · $308k · 2003–2007

• The Development of Adaptive Embryo Behavior

  NSF · $951k · 2014–2022

• Dissertation Research: Parent-embryo Interactions in Glassfrogs - Female Mating Strategies, Paternal Effort, and Adaptive Plasticity in Hatching

  NSF · $16k · 2015–2016

• DISSERTATION RESEARCH: Cues and Signals - Vibrational Information in Two Life Stages of the Red-Eyed Treefrog

  NSF · $10k · 2007–2008

Frequent coauthors

• Justin C. Touchon

  Vassar College

  38 shared

• Iván Gómez-Mestre

  Estación Biológica de Doñana

  29 shared

• Brandon A. Güell

  Boston University

  28 shared

• James R. Vonesh

  Virginia Commonwealth University

  26 shared

• Michael McCoy

  26 shared

• J. Gregory McDaniel

  24 shared

• Julie Jung

  University of Utah

  19 shared

• Michael S. Caldwell

  13 shared

Education

• PhD, Zoology

  University of Texas System

  1998

• MSc, Biology

  Dalhousie University

  1990

• BSc, Biology

  University of Guelph

  1985