Alex Baugh
Associate Professor Swarthmore College
Research
Integrating ecology, evolution and behavior
Evolution doesn’t tune one dial at a time. Real animals are integrated systems: metabolism, motivation, risk tolerance, sensory tuning, and signaling behavior often come packaged because they share underlying mechanisms and because selection can favor particular combinations of traits (Cheverud, 1982; Lande & Arnold, 1983). The question isn’t simply which traits vary, but what coordinates that variation—and when that coordination enables adaptation versus when it imposes constraint.
That’s where hormones are unusually illuminating. Endocrine systems broadcast body-wide information about state (energy balance, stress load, reproductive readiness) and can reorganize and prioritize multiple tissues at once. In that sense, hormones function as choreographers of trait suites: they can produce integrated, repeatable phenotypes (phenotypic integration) while still allowing context-sensitive plasticity (McGlothlin & Ketterson, 2008; Baugh et al., 2012). This is precisely the layer where mechanistic explanations start to become evolutionary predictions (i.e. where how grades into why)—because shared regulators can generate correlations among traits, shape trade-offs, and bias which phenotypic “packages” are easiest (or hardest) for selection to build or modify (Hau et al., 2016).
Across our work in behavioral endocrinology, eco-physiology, and animal communication, we treat endocrine signals as both readouts and levers: measurable markers of state, and experimental handles for causal tests. We are especially interested in how animals commit to energetically demanding behaviors (e.g., migration, reproductive signaling, mate choice) and how they switch when conditions change—often under social and environmental challenge (Romero et al., 2009). A distinctive feature of our approach is that we treat ongoing behavior as a causal input to endocrine activity (physiology–behavior coupling), not merely a downstream consequence of hormone levels (Wingfield et al., 1990; Baugh, 2024).
Questions we keep coming back to
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When do endocrine regulators generate hormone-mediated trait suites (pleiotropy that can facilitate—or constrain—adaptation)?
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What do dose–response functions look like—thresholds, saturation, or smooth continua—and what does that imply for evolvability and individual differences?
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When do elevated hormones create physiological inertia that buffers commitment against short-term disruption?
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Are entry vs exit from a behavioral state controlled by different mechanisms (hysteresis), making “turning on” distinct from “turning off”?
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Can targeted manipulations of endocrine and energetic systems “engineer” phenotypes to decompose trait architecture and expose hidden constraints and trade-offs? (Arnold, 1983; Zera & Harshman, 2001)
Recent and On-Going Projects
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I am collaborating with Drs. Pablo Salmon (Institute for Avian Research, Germany) and Jesko Partecke (Max Planck Institute for Animal Behavior, Germany) on projects aimed at elucidating the physiological mechanisms that underlie one of the greatest athletic feats in the natural world: long distance migration. We are evaluating the metabolic correlates of migratory behavior using biotelemetry in wild and captive birds along with cellular respirometry and endocrine activity.
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Previously, I demonstrated that male gray treefrogs in amplexus have substantially higher circulating concentrations of androgens, estrogens and glucocorticoids compared to adjacent solo males. Now, I am collaborating with Dr. Megan Freiler (Post-doc) and Prof. Mark Bee to experimentally test the hypothesis that the motor act of clasping itself drives these elevated and correlated hormones.
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Individuals differ in how they respond to stressors. Some react with a rapid onset of glucocorticoids (“stress hormones”) and those individuals also tend to retain elevated concentrations for long after the stressor is removed, and vice versa. What are the underlying mechanisms that explain such individual variation? In this domain my lab explores how variation in hormone receptor expression in the HPA axis maps onto these variable dynamics and how those physiological differences are related to behavioral coping.
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Working with Mark Bee (UMN) and Chris Leary (Ole Miss) we are attempting to understand the independent and interactive effects of glucocorticoids and androgens on male vocal behavior using field experiments in Cope’s grey treefrogs.
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My lab is developing techniques to estimate concentrations of hormones in frogs without the collection of tissues. We are currently using spadefoot toads 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 determined that brief, non-invasive water borne methods can effectively estimate biologically informative concentrations of multiple steroid hormones in three amphibian species.
Hyla versicolor
Tungara frog
Couch’s Spadefoot
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I am working with Alex Jordan’s research group in the Collective Behavior department at the Max Planck Institute for Animal Behavior at the University of Konstanz. We are developing techniques and testing hypotheses related to social transmission of hormones via water-borne steroids across a clade of cichlid fishes from Lake Tanganyika. So far we have demonstrated that we can precisely measure excreted cortisol in four related cichlid species that vary in their gregarious habits. Remarkably, these big differences in sociality appear unrelated the stress of social isolation. Perhaps being alone is not the same thing as being lonely in a shell-dweller.
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Here we are testing the influence of glucocorticoids on female mate choice and how the circulating concentrations of steroids interact with the expression of steroid receptors in the brain to explain behavioral effects.
Pair of H. chrysoscelis in amplexus
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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.
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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.
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.