Karen M. Warkentin, M.Sc., Ph.D. - US grants

Many prey have plastic defenses that they use only when at risk of predation, otherwise saving the costs of defense. In some contexts, these plastic responses and their costs can have surprisingly large consequences both for individuals later in life and for population dynamics. In other contexts the lethal effects of predation matter much more. This collaborative project focuses on predator-induced plasticity in hatching and metamorphosis, two ecologically pivotal events that exemplify the life-stage transitions common among animals. The focal species, red-eyed treefrogs, hatch early to escape egg predators, metamorphose early in response to tadpole predators, and delay metamorphosis in response to predators of froglets. The project uses mathematical models and field experiments integrated across these three life stages to assess how environmental context shapes the relative importance of plastic responses to risk and direct predation for both population dynamics and individual fitness.

This will advance understanding of population ecology, life history, and development, and strengthen links among these fields. It will directly support a postdoctoral researcher, 2-3 graduate students, and 6 undergraduate interns, and provide research opportunities for 15-20 more undergraduates. Students will gain cross-cultural experience and training in tropical field biology and ecology. Results will be broadly disseminated - the Principal Investigator's prior research has been widely reported in the popular media and in textbooks.

The strategies that animals use to extract information from social signals likely differ from the strategies that they use to extract information from the non-social environment. This study compares strategies for assessing vibrational cues and signals used by embryo and adult red-eyed treefrogs. Embryos use vibrational cues to detect predators, and to escape, but must distinguish these vibrations from harmless disturbances, such as rain. Adults vibrate their bodies in a dramatic signal used during contests between males over calling sites. Thus, there are unique opportunities to: (i) compare strategies for extracting information from vibrational signals and cues used in the same environment, (ii) examine how vibrational information is used by embryos and adults of the same frog species, (iii) study vibrational communication in vertebrates. The proposed research focuses on the newly discovered vibrational display of adults. The structure of this signal, and the information it contains, will be investigated using video and vibration recordings of aggressive interactions between males. Then, visual and vibrational parts of the signal will be played back to frogs to explore how these parts interact to carry information, to test whether vibrations help males locate signaling rivals, and to test whether males pay attention to signal frequency and duration. Comparing the ways animals interpret signals and cues will help us understand how signals evolve. This project also contributes more broadly to the emerging field of biological vibrations research by developing novel techniques for recording and playback of vibrations. The research provides opportunities for participation of US undergraduates and high school students in Boston and Panama. The PIs are committed to broad dissemination of results to both the academic community and the public through professional and educational presentations as well as cooperation with documentary media projects.

Understanding the processes that maintain biodiversity is of fundamental importance to ecologists and conservationists. In spatially structured habitats, ranging from tidal pools to forest fragments, explaining patterns of species distribution and abundance requires investigation of processes occurring at different spatial scales. Locally, predatory and competitive interactions affect species presence within habitats. Regionally, dispersal and colonization influence species presence across habitats. Processes at both scales likely contribute to the patterns of diversity and distribution observed in nature, however, their relative importance is not well understood. This study will evaluate the contributions of local and regional processes to patterns of variation among local communities. The community under investigation consists of four insects associated with red-eyed treefrog egg masses: a social wasp that eats frog eggs; two flies whose larvae infest egg masses; and a parasitoid wasp that attacks fly larvae. Research will examine 1) locally, how competition and parasitism influence the identity and abundance of insects emerging from egg masses and 2) regionally, how damage caused by egg-eating wasps (which is attractive to flies) and the spatial arrangement of egg masses influence where insects colonize. This research fills an important gap in our understanding of how local interactions and spatial dynamics combine to explain patterns of distribution and abundance. This dissertation trains one doctoral student as well as assistants from the US and Latin America. Results will be broadly disseminated to scientific audiences and used in public outreach and educational presentations in the US and in Panama.

Embryos of many species assess and respond to their environment in ways that matter for survival. Many features and challenges of embryonic life are broadly shared across animals, but frog eggs are particularly tractable to study. Structures such as egg capsules protect and constrain the embryo inside, creating a trade-off of costs and benefits. Upon hatching, animals enter a new environment, with both new dangers and resources. When to hatch is an essential decision embryos make, based on environmental cues. Hatching is also a physical feat that embryos must perform. The ability to assess cues, to exit the egg, and to survive outside the egg all change as embryos develop. Thus, under the same conditions, what embryos can do and what they should do to survive also changes. This project will examine how and why development changes behavior, using embryos of red-eyed treefrogs that hatch up to 40% prematurely to escape threats to the egg. It will assess the importance of maturation, adaptive changes in decisions matched to abilities, embryonic learning, and how embryos use two kinds of information; simple cues of oxygen availability and complex vibrations that can indicate predator attack. It will improve our understanding of embryo lives, behavioral development, and how animals use different kinds of information to make decisions, including broadly important but poorly understood vibrational information. The adaptive behavior of embryos is accessible and appealing, and thus ideal for scientific education and outreach. This project will offer interdisciplinary biology-engineering training for graduate and undergraduate students, as well as Neotropical research and cross-cultural experiences for US students and Latin American interns. The PIs will work with the media, museums, and zoos to disseminate results broadly. They will offer research experiences for teachers and develop online multimedia resources for educators at multiple levels. New methods and tools developed by this project will facilitate other research on embryo behavior and animal responses to vibrational cues.

This project is an integrative study of the development and regulation of environmentally cued hatching in red-eyed treefrogs, for which multiple selective trade-offs shaping hatching timing are known. Embryos use cues in at least two sensory modalities for their hatching decision. Older embryos hatch more readily, but even 30%-premature embryos sometimes hatch within seconds of a cue. This project will assess: I) how the speed and success of hatching change across effector development, focusing on hatching glands; II) how sensor development changes sensitivity to cues and cue properties, addressing developmental changes in mechanoreception by the inner ear and lateral line vs. more consistent, early developed, oxygen sensing; and III) how hatching decision rules for responses to simple hypoxia cues and complex vibrational, and potentially tactile, physical disturbance cues are shaped by developmentally changing trade-offs, a history of stage-specific selection, and the earlier experiences of embryos. The team will use (a) histology and microscopy to characterize morphological changes, (b) respirometry to assess metabolic changes, (c) measures of vestibulo-ocular reflexes to assess otic function, and (d) macro-videography to analyze embryo behavior and hatching performance. They will assess ontogenetic changes in hatching under controlled hypoxia, vibration playback, and predator attacks, and develop new playback methods for separating motion and tactile components of physical disturbance cues. Mechanosensory stimuli and hypoxia are common cues for hatching across taxa. Moreover, vibrational signals and cues inform behavior in many other contexts, later in life, and oxygen availability shapes the behavior of many aquatic animals. Results from red-eyed treefrog embryos will advance our understanding of behavioral development and animal information use more broadly. Datasets will be deposited in DRYAD. Outreach materials, including images and video, will be posted on Warkentin's lab website or contributed to the Encyclopedia of Life or National Association of Biology Teachers web resource page.

A fundamental goal of behavioral ecology is to understand how shared interests and conflicts among related individuals shape family life. Offspring benefit from increasing parental care, but parents' ability to care for young is limited by resources needed for future reproduction and survival. This conflict is thought to favor strategies that allow individuals to balance the costs and benefits of parenting. Research on this topic has typically focused on species with conventional sex roles where females care for young. In glassfrogs, males care for eggs and embryos can hatch early to escape from abandoned eggs. This project will evaluate hypotheses about father embryo co-evolution by assessing heritability and variation in ecologically important paternal and embryonic traits. It will test if females select good fathers or mate strategically to induce good parenting and how interactions between parents affect the evolution of embryos' hatching strategies. This project will offer new perspectives on family life by testing how sexual selection influences the behavior of fathers and embryos. Glassfrog family interactions have substantial appeal for scientific education and public outreach. The PIs will work with the media, museums, and zoos to disseminate results broadly. This project will offer training in integrative methods of genomics, behavioral ecology, and quantitative genetics for a graduate student and an undergraduate assistant and foster collaborations with Latin American researchers.

This research uses adaptive plasticity in hatching to examine parent offspring interactions and their consequences in a glassfrog with male care of eggs. In Hyalinobatrachium colymbiphyllum, higher mating success results in more paternal effort, longer embryonic periods, and higher offspring survival. The team will use a next-generation genotype-by-sequencing method for maternity analysis, in combination with detailed histories of male mating and caring behavior, to assess female mating choices in the context of social environments. Specifically, they will test whether females mate tactically to exploit male care and assess potential mutual benefits to co-nesting females. The team will test hypotheses of father embryo co-evolution by assessing covariation between paternal traits, measured in a field experiment, and hatching responses of their embryos, measured in a common-garden experiment. This study extends fundamental tests of parent offspring interactions to a system with male-only care, and will inform and motivate other research on parental and embryo strategies. Data will be shared in online supplements to publications or in public archives (DRYAD, the Sequence Read Archive, GenBank) as appropriate. Outreach materials will be posted online.