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Research

Research Scope

We examine the causes and consequences of animal behavior, and do so by integrating across the traditional disciplines of behavioral ecology, neuroethology and environmental endocrinology.

One stream of our research centers on understanding the forces that generate and maintain individual (co)variation in decision making (e.g., communication and coping behavior) and its physiological regulation (e.g., sensory processing and stress reactivity) in wild animals. We take an ecological approach, testing evolutionary hypotheses in the context of an organism’s natural environment. The types of questions we explore include:

  • Which behavioral traits are stable versus plastic, and what are the extrinsic (environmental) and intrinsic (physiological and neural) bases of such variation?
  • What are the developmental factors and sensitive periods that sculpt behavioral and physiological variation, and which environmental and experiential factors influence developmental trajectories and impact fitness?

While the study of single traits has proven fruitful, the study of animal behavior has become increasingly interested in understanding higher order traits, including suites of correlated characters. This is essential in order to understand the targets on which natural and sexual selection may act. Therefore we also explore questions such as:

  • Do regulatory systems, such as steroid hormones, exert pleiotropic effects and hence generate suites of correlated behavioral traits?
  • By manipulating the physiological systems that regulate behavior, can we engineer phenotypes in order to experimentally decompose and thus understand the structure of behavior and the trade-offs organisms face?

In the domain of animal communication, our model systems include acoustic signaling and auditory behavior in anuran amphibians (frogs and toads). We test hypotheses about the physiological basis for reproductive decision making (acoustic signaling and acoustically-guided behavior).

In the domain of behavioral endocrinology, we seek to understand the intrinsic and experience-dependent factors that organize and activate behavioral responses to challenge, such as exposure to environmental and social stressors.

Current Projects

  • How does the endocrine stress axis modulate female mate choice behavior?

    Do experimental elevations in plasma corticosterone modulate female choosiness and how do neuroendocrine markers predict such changes?

    Working in collaboration with Mark Bee (University of Minnesota) and Megan Gall (Vassar College), we are testing the influence of experimentally elevated concentrations of corticosterone on female choosiness in a dynamic mate choice assay, and how the circulating concentrations of steroids interact with the expression of steroid receptors in the brain to explain behavioral effects.

  • How do urban environments impact tungara frog breeding biology?

    The behavioral, ecological and physiological impacts of urban environments on tungara frogs: what causes urban males to be more risk-taking?

    This project (CITISENSE), which is led by Wouter Halfwerk aims to uncover the basis (heritable and acquired traits) for differences in urban and forest dwelling tungara frogs. The urban populations (e.g. in Panama City) express more risk-taking behavior compared to their forest counterparts. This multi-institution collaboration aims to identify the source of this population variation, including a look at differences in the hormonal milieu.

  • Neural and hormonal regulation of female receptivity signaling in brown-headed cowbirds

    How do steroid hormones and the nervous system regulate female sexual receptivity and preference?

    This is a collaboration with labs at the University of Pennsylvania, including the Schmidt Lab, and with the White Lab at Wilfrid Laurier University. We are investigating the neural and hormonal control of female copulation solicitation displays and how female and male interactions influence group dynamics.

  • The difference a day makes: phenotypic shifts after breeding in Cope's gray treefrog

    Does brain, physiology and behavior shift rapidly after an female frog breeds?

    Mating is typically a brief and key life history chapter in a sexually reproducing animal’s life. Because successful reproduction requires a set of essential adaptations that are less important during a non-breeding period, we expect substantial phenotypic remodeling during this transition, and for these shifts to occur in a coordinated fashion (i.e. phenotypic integration). For example, receivers need to be able to detect and discriminate conspecific advertisement signals before choosing a mate and copulating, and thus need a suite of sensory and behavioral adaptations to subserve those tasks. Once a seasonally breeding female has mated, however, these traits may shift in order to support other lifestyle needs.

    This project is a collaboration with Drs. Mark Bee (Univ. Minnesota) and Megan Gall (Vassar College). We are testing this hypothesis of phenotypic integration using wild-caught female Cope’s gray treefrogs (Hyla chrysoscelis) and evaluating how three trait categories shift over the course of a single day following mating: behavioral (phonotaxis), neural (auditory thresholds) and endocrinological (glucocorticoids, testosterone, estradiol); and how these three levels of the phenotype interact.

  • Non-invasive endocrinology in amphibians

    Can we estimate hormone status from a water sample?

    My lab is developing techniques to estimate concentrations of hormones in frogs without the collection of tissues. We are currently using treefrogs and tungara frogs to establish and validate effective methods for steroid collection, extraction and quantification and we are now applying this non-invasive method to problems in behavioral endocrinology and conservation physiology in the lab and field. Thus far we have extensively validated four steroids: corticosterone, estradiol, progesterone and testosterone.

  • How female frogs choose their mates

    Why are some females choosier than others?

    Few decisions in life are more consequential than the choice of a mate. Sexually reproducing animals ensure passage of their genes to the next generation by choosing compatible mates, which often rests on species-specific perception of communication signals. In addition to species and sex recognition, females favor certain males over others, thus generating sexual selection for attractive traits. But this process of decision making is predictably complex: it is subject to a variety of influences, including the effects of developmental experience, immediate physiological condition, environmental context and the past evolutionary history of the organism. We study vocal communication and auditory perception in anuran amphibians (grey tree frogs and tungara frogs) as tractable models for decomposing the decision-making process and identifying the forces shaping behavioral phenotypes.

  • Stress physiology in songbirds

    Why do some individuals cope better than others?

    Wild organisms encounter myriad dangers and opportunities in their everyday lives. Whether it’s deciding to engage in conflict with a territorial neighbor or explore a novel prey item, taking risks inherently involves trade-offs. In our rapidly changing world, the nature and magnitude of stressors impinging upon wild populations is poorly understood but of exceptional relevance. We do know, however, that there is often remarkable standing variation in the capacity for flexibility in individuals. And yet, we now know that behavioral flexibility is not unlimited: while a given individual might exhibit flexibility in behavior over time, their average response often differs from other individuals in the population. What are the causes (proximate and ultimate) of these inter-individual differences? Our on-going projects test hypotheses about the inter-relationships among neural, hormonal and behavioral variation in wild and captive great tits (Parus major). Research is carried out at the Max Planck Institute for Ornithology in Radolfzell and Seewiesen, Germany, the Netherlands Institute for Ecology in Wageningen, the Netherlands, and here at Swarthmore.