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Bailey ML, Nixon C, Rusch DB, Buechlein A, Rosvall KA, Bentz AB. Maternal social environment shapes yolk testosterone allocation and embryonic neural gene expression in tree swallows. Horm Behav 2024; 163:105561. [PMID: 38759417 DOI: 10.1016/j.yhbeh.2024.105561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Revised: 05/03/2024] [Accepted: 05/06/2024] [Indexed: 05/19/2024]
Abstract
Offspring from females breeding in competitive social environments are often exposed to more testosterone (T) during embryonic development, which can affect traits from growth to behavior in potentially adaptive ways. Despite the important role of maternally derived steroids in shaping offspring development, the molecular mechanisms driving these processes are currently unclear. Here, we use tree swallows (Tachycineta bicolor) to explore the effects of the maternal social environment on yolk T concentrations and genome-wide patterns of neural gene expression in embryos. We measured aggressive interactions among females breeding at variable densities and collected their eggs at two timepoints, including the day laid to measure yolk T concentrations and on embryonic day 11 to measure gene expression in whole brain samples. We found that females breeding in high-density sites experienced elevated rates of physical aggression and their eggs had higher yolk T concentrations. A differential gene expression and weighted gene co-expression network analysis indicated that embryos from high-density sites experienced an upregulation of genes involved in hormone, circulatory, and immune processes, and these gene expression patterns were correlated with yolk T levels and aggression. Genes implicated in neural development were additionally downregulated in embryos from high-density sites. These data highlight how early neurogenomic processes may be affected by the maternal social environment, giving rise to phenotypic plasticity in offspring.
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Affiliation(s)
- M Leigh Bailey
- School of Biological Sciences, University of Oklahoma, Norman, OK 73019, USA
| | - Cameron Nixon
- School of Biological Sciences, University of Oklahoma, Norman, OK 73019, USA
| | - Douglas B Rusch
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN, USA
| | - Aaron Buechlein
- Center for Genomics and Bioinformatics, Indiana University, Bloomington, IN, USA
| | | | - Alexandra B Bentz
- School of Biological Sciences, University of Oklahoma, Norman, OK 73019, USA; Department of Biology, Indiana University, Bloomington, IN 47405, USA.
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Taff CC, McNew SM, Zimmer C, Uehling JJ, Houtz JL, Ryan TA, Chang van Oordt D, Injaian AS, Vitousek MN. Social signal manipulation and environmental challenges have independent effects on physiology, internal microbiome, and reproductive performance in tree swallows (Tachycineta bicolor). JOURNAL OF EXPERIMENTAL ZOOLOGY. PART A, ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY 2023; 339:723-735. [PMID: 37306329 DOI: 10.1002/jez.2722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Revised: 04/10/2023] [Accepted: 05/25/2023] [Indexed: 06/13/2023]
Abstract
The social environment that individuals experience appears to be a particularly salient mediator of stress resilience, as the nature and valence of social interactions are often related to subsequent health, physiology, microbiota, and overall stress resilience. Relatively few studies have simultaneously manipulated the social environment and ecological challenges under natural conditions. Here, we report the results of experiments in wild tree swallows (Tachycineta bicolor) in which we manipulated both ecological challenges (predator encounters and flight efficiency reduction) and social interactions (by experimental dulling of a social signal). In two experiments conducted in separate years, we reversed the order of these treatments so that females experienced either an altered social signal followed by a challenge or vice-versa. Before, during, and after treatments were applied, we tracked breeding success, morphology and physiology (mass, corticosterone, and glucose), nest box visits via an RFID sensor network, cloacal microbiome diversity, and fledging success. Overall, we found that predator exposure during the nestling period reduced the likelihood of fledging and that signal manipulation sometimes altered nest box visitation patterns, but little evidence that the two categories of treatment interacted with each other. We discuss the implications of our results for understanding what types of challenges and what conditions are most likely to result in interactions between the social environment and ecological challenges.
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Affiliation(s)
- Conor C Taff
- Department of Ecology & Evolutionary Biology and Lab of Ornithology, Cornell University, Ithaca, New York, USA
| | - Sabrina M McNew
- Department of Ecology & Evolutionary Biology and Lab of Ornithology, Cornell University, Ithaca, New York, USA
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, USA
| | - Cedric Zimmer
- Laboratoire d'Ethologie Expérimentale et Comparée, University Sorbonne Paris Nord, Paris, France
| | - Jennifer J Uehling
- Department of Ecology & Evolutionary Biology and Lab of Ornithology, Cornell University, Ithaca, New York, USA
| | - Jennifer L Houtz
- Department of Ecology & Evolutionary Biology and Lab of Ornithology, Cornell University, Ithaca, New York, USA
| | - Thomas A Ryan
- Department of Ecology & Evolutionary Biology and Lab of Ornithology, Cornell University, Ithaca, New York, USA
| | - David Chang van Oordt
- Department of Ecology & Evolutionary Biology and Lab of Ornithology, Cornell University, Ithaca, New York, USA
| | | | - Maren N Vitousek
- Department of Ecology & Evolutionary Biology and Lab of Ornithology, Cornell University, Ithaca, New York, USA
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3
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Smiley KO, Lipshutz SE, Kimmitt AA, DeVries MS, Cain KE, George EM, Covino KM. Beyond a biased binary: A perspective on the misconceptions, challenges, and implications of studying females in avian behavioral endocrinology. Front Physiol 2022; 13:970603. [PMID: 36213250 PMCID: PMC9532843 DOI: 10.3389/fphys.2022.970603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Accepted: 08/18/2022] [Indexed: 12/04/2022] Open
Abstract
For decades, avian endocrinology has been informed by male perspectives and male-focused research, leaving significant gaps in our understanding of female birds. Male birds have been favored as research subjects because their reproductive behaviors are considered more conspicuous and their reproductive physiology is presumably less complex than female birds. However, female birds should not be ignored, as female reproductive behavior and physiology are essential for the propagation of all avian species. Endocrine research in female birds has made much progress in the last 20 years, but a substantial disparity in knowledge between male and female endocrinology persists. In this perspective piece, we provide examples of why ornithology has neglected female endocrinology, and we propose considerations for field and laboratory techniques to facilitate future studies. We highlight recent advances that showcase the importance of female avian endocrinology, and we challenge historic applications of an oversimplified, male-biased lens. We further provide examples of species for which avian behavior differs from the stereotypically described behaviors of male and female birds, warning investigators of the pitfalls in approaching endocrinology with a binary bias. We hope this piece will inspire investigators to engage in more comprehensive studies with female birds, to close the knowledge gap between the sexes, and to look beyond the binary when drawing conclusions about what is ‘male’ versus ‘female’ biology.
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Affiliation(s)
- Kristina O. Smiley
- Centre for Neuroendocrinology and Department of Anatomy, School of Biomedical Sciences, University of Otago, Dunedin, New Zealand
- Center for Neuroendocrine Studies and Department of Psychological and Brain Sciences, University of Massachusetts-Amherst, Amherst, MA, United States
- *Correspondence: Kristina O. Smiley,
| | - Sara E. Lipshutz
- Biology Department, Loyola University Chicago, Chicago, IL, United States
| | - Abigail A. Kimmitt
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, United States
| | - M. Susan DeVries
- Department of Biological Sciences, University of Wisconsin-Whitewater, Whitewater, WI, United States
| | - Kristal E. Cain
- School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Elizabeth M. George
- Biology Department, Texas A&M University, College Station, TX, United States
| | - Kristen. M. Covino
- Biology Department, Loyola Marymount University, Los Angeles, CA, United States
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4
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George EM, Rosvall KA. Bidirectional relationships between testosterone and aggression: a critical analysis of four predictions. Integr Comp Biol 2022; 62:icac100. [PMID: 35759399 PMCID: PMC9494517 DOI: 10.1093/icb/icac100] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 06/05/2022] [Accepted: 06/09/2022] [Indexed: 12/12/2022] Open
Abstract
Experimentally elevated testosterone (T) often leads to enhanced aggression, with examples across many different species, including both males and females. Indeed, the relationship between T and aggression is among the most well-studied and fruitful areas of research at the intersection of behavioral ecology and endocrinology. This relationship is also hypothesized to be bidirectional (i.e., T influences aggression, and aggression influences T), leading to four key predictions: (1) Individuals with higher T levels are more aggressive than individuals with lower T. (2) Seasonal changes in aggression mirror seasonal changes in T secretion. (3) Aggressive territorial interactions stimulate increased T secretion. (4) Temporary elevations in T temporarily increase aggressiveness. These predictions cover a range of timescales, from a single snapshot in time, to rapid fluctuations, and to changes over seasonal timescales. Adding further complexity, most predictions can also be addressed by comparing among individuals or with repeated sampling within-individuals. In our review, we explore how the spectrum of results across predictions shapes our understanding of the relationship between T and aggression. In all cases, we can find examples of results that do not support the initial predictions. In particular, we find that predictions 1-3 have been tested frequently, especially using an among-individual approach. We find qualitative support for all three predictions, though there are also many studies that do not support predictions 1 and 3 in particular. Prediction 4, on the other hand, is something that we identify as a core underlying assumption of past work on the topic, but one that has rarely been directly tested. We propose that when relationships between T and aggression are individual-specific or condition-dependent, then positive correlations between the two variables may be obscured or reversed. In essence, even though T can influence aggression, many assumed or predicted relationships between the two variables may not manifest. Moving forward, we urge greater attention to understanding how and why it is that these bidirectional relationships between T and aggression may vary among timescales and among individuals. In doing so, we will move towards a deeper understanding on the role of hormones in behavioral adaptation.
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Affiliation(s)
- Elizabeth M George
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
- Center for the Integrated Study of Animal Behavior, Indiana University, Bloomington, IN 47405, USA
| | - Kimberly A Rosvall
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
- Center for the Integrated Study of Animal Behavior, Indiana University, Bloomington, IN 47405, USA
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George EM, Wolf SE, Bentz AB, Rosvall KA. Testing hormonal responses to real and simulated social challenges in a competitive female bird. Behav Ecol 2022; 33:233-244. [PMID: 35210941 PMCID: PMC8857935 DOI: 10.1093/beheco/arab129] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2021] [Revised: 09/14/2021] [Accepted: 10/18/2021] [Indexed: 08/25/2024] Open
Abstract
Competitive interactions often occur in series; therefore animals may respond to social challenges in ways that prepare them for success in future conflict. Changes in the production of the steroid hormone testosterone (T) are thought to mediate phenotypic responses to competition, but research over the past few decades has yielded mixed results, leading to several potential explanations as to why T does not always elevate following a social challenge. Here, we measured T levels in tree swallows (Tachycineta bicolor), a system in which females compete for limited nesting cavities and female aggression is at least partially mediated by T. We experimentally induced social challenges in two ways: (1) using decoys to simulate territorial intrusions and (2) removing subsets of nesting cavities to increase competition among displaced and territory-holding females. Critically, these experiments occurred pre-laying, when females are physiologically capable of rapidly increasing circulating T levels. However, despite marked aggression in both experiments, T did not elevate following real or simulated social challenges, and in some cases, socially challenged females had lower T levels than controls. Likewise, the degree of aggression was negatively correlated with T levels following a simulated territorial intrusion. Though not in line with the idea that social challenges prompt T elevation in preparation for future challenges, these patterns nevertheless connect T to territorial aggression in females. Coupled with past work showing that T promotes aggression, these results suggest that T may act rapidly to allow animals to adaptively respond to the urgent demands of a competitive event.
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Affiliation(s)
- Elizabeth M George
- Department of Biology, Indiana University Bloomington, Bloomington, IN, USA
| | - Sarah E Wolf
- Department of Biology, Indiana University Bloomington, Bloomington, IN, USA
| | - Alexandra B Bentz
- Department of Biology, Indiana University Bloomington, Bloomington, IN, USA
| | - Kimberly A Rosvall
- Department of Biology, Indiana University Bloomington, Bloomington, IN, USA
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