1
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Little AG, Seebacher F. A review of the empirical evidence for costs of plasticity in ectothermic animals. J Exp Biol 2025; 228:jeb249226. [PMID: 39783040 DOI: 10.1242/jeb.249226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2025]
Abstract
Phenotypic plasticity can represent a vital adaptive response to environmental stressors, including those associated with climate change. Despite its evolutionary advantages, the expression of plasticity varies significantly within and among species, and is likely to be influenced by local environmental conditions. This variability in plasticity has important implications for evolutionary biology and conservation physiology. Theoretical models suggest that plasticity might incur intrinsic fitness costs, although the empirical evidence is inconsistent and there is ambiguity in the term 'cost of plasticity'. Here, we systematically review the literature to investigate the prevalence of costs associated with phenotypic plasticity in ectothermic animals. We categorized studies into those assessing 'costs of phenotype' (trade-offs between different plastic trait values) and 'costs of plasticity' (intrinsic costs of the capacity for plasticity). Importantly, the experimental designs required to detect costs of plasticity are inherently more complex and onerous than those required to detect costs of phenotype. Accordingly, our findings reveal a significant focus on costs of phenotype over costs of plasticity, with the former more frequently detecting costs. Contrary to theoretical expectations, our analysis suggests that costs of plasticity are neither universal nor widespread. This raises questions about the evolutionary dynamics of plasticity, particularly in stable environments. Our analysis underscores the need for precise terminology and methodology in researching costs of plasticity, to avoid conflating costs associated with plastic traits with costs more intrinsic to plasticity. Understanding these nuances is crucial for predicting how species might adapt to rapidly changing environments.
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Affiliation(s)
- Alexander G Little
- Department of Biology, Life Sciences Building, McMaster University, Hamilton, ON, Canada, L8S 4K1
| | - Frank Seebacher
- School of Life and Environmental Sciences, A08 , University of Sydney, Sydney, NSW 2006, Australia
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2
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Taff CC, Baldan D, Mentesana L, Ouyang JQ, Vitousek MN, Hau M. Endocrine flexibility can facilitate or constrain the ability to cope with global change. Philos Trans R Soc Lond B Biol Sci 2024; 379:20220502. [PMID: 38310929 PMCID: PMC10838644 DOI: 10.1098/rstb.2022.0502] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2023] [Accepted: 11/21/2023] [Indexed: 02/06/2024] Open
Abstract
Global climate change has increased average environmental temperatures world-wide, simultaneously intensifying temperature variability and extremes. Growing numbers of studies have documented phenological, behavioural and morphological responses to climate change in wild populations. As systemic signals, hormones can contribute to orchestrating many of these phenotypic changes. Yet little is known about whether mechanisms like hormonal flexibility (reversible changes in hormone concentrations) facilitate or limit the ability of individuals, populations and species to cope with a changing climate. In this perspective, we discuss different mechanisms by which hormonal flexibility, primarily in glucocorticoids, could promote versus hinder evolutionary adaptation to changing temperature regimes. We focus on temperature because it is a key gradient influenced by climate change, it is easy to quantify, and its links to hormones are well established. We argue that reaction norm studies that connect individual responses to population-level and species-wide patterns will be critical for making progress in this field. We also develop a case study on urban heat islands, where several key questions regarding hormonal flexibility and adaptation to climate change can be addressed. Understanding the mechanisms that allow animals to cope when conditions become more challenging will help in predicting which populations are vulnerable to ongoing climate change. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'.
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Affiliation(s)
- Conor C. Taff
- Laboratory Ornithology and Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
- Department of Biology, Colby College, Waterville, ME 04901, USA
| | - Davide Baldan
- Department of Biology, University of Nevada, Reno, NV 89557, USA
| | - Lucia Mentesana
- Evolutionary Physiology, Max Planck Institute for Biological Intelligence, 82319 Seewiesen, Germany
- Faculty of Sciences, Republic University, Montevideo, 11200, Uruguay
| | - Jenny Q. Ouyang
- Department of Biology, University of Nevada, Reno, NV 89557, USA
| | - Maren N. Vitousek
- Laboratory Ornithology and Department of Ecology & Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
| | - Michaela Hau
- Evolutionary Physiology, Max Planck Institute for Biological Intelligence, 82319 Seewiesen, Germany
- Department of Biology, University of Konstanz, Konstanz, 78467, Germany
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3
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Radley JJ, Herman JP. Preclinical Models of Chronic Stress: Adaptation or Pathology? Biol Psychiatry 2023; 94:194-202. [PMID: 36631383 PMCID: PMC10166771 DOI: 10.1016/j.biopsych.2022.11.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 10/15/2022] [Accepted: 11/02/2022] [Indexed: 11/11/2022]
Abstract
The experience of prolonged stress changes how individuals interact with their environment and process interoceptive cues, with the end goal of optimizing survival and well-being in the face of a now-hostile world. The chronic stress response includes numerous changes consistent with limiting further damage to the organism, including development of passive or active behavioral strategies and metabolic adjustments to alter energy mobilization. These changes are consistent with symptoms of pathology in humans, and as a result, chronic stress has been used as a translational model for diseases such as depression. While it is of heuristic value to understand symptoms of pathology, we argue that the chronic stress response represents a defense mechanism that is, at its core, adaptive in nature. Transition to pathology occurs only after the adaptive capacity of an organism is exhausted. We offer this perspective as a means of framing interpretations of chronic stress studies in animal models and how these data relate to adaptation as opposed to pathology.
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Affiliation(s)
- Jason J Radley
- Department of Psychological and Brain Sciences, Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa
| | - James P Herman
- Department of Pharmacology and Systems Physiology, University of Cincinnati, Cincinnati, Ohio; Cincinnati Veterans Administration Medical Center, Cincinnati, Ohio.
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4
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Vitousek MN, Dantzer B, Fuxjager MJ, Schlinger BA. Evolutionary behavioral endocrinology: Introduction to the special issue. Horm Behav 2023; 152:105356. [PMID: 37031556 DOI: 10.1016/j.yhbeh.2023.105356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 04/11/2023]
Affiliation(s)
- Maren N Vitousek
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, United States of America; Cornell Lab of Ornithology, Ithaca, NY 14850, United States of America
| | - Ben Dantzer
- Department of Psychology, University of Michigan, Ann Arbor, MI 48109, United States of America; Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, United States of America
| | - Matthew J Fuxjager
- Department of Ecology, Evolution, and Organismal Biology, Brown University, Providence, RI 02912, United States of America
| | - Barney A Schlinger
- Department of Integrative Biology and Physiology, UCLA, Los Angeles, CA 90095, United States of America; Department of Ecology and Evolutionary Biology, UCLA, Los Angeles, CA 90095, United States of America.
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5
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Dantzer B. Frank Beach Award Winner: The centrality of the hypothalamic-pituitary-adrenal axis in dealing with environmental change across temporal scales. Horm Behav 2023; 150:105311. [PMID: 36707334 DOI: 10.1016/j.yhbeh.2023.105311] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2022] [Revised: 01/02/2023] [Accepted: 01/06/2023] [Indexed: 01/26/2023]
Abstract
Understanding if and how individuals and populations cope with environmental change is an enduring question in evolutionary ecology that has renewed importance given the pace of change in the Anthropocene. Two evolutionary strategies of coping with environmental change may be particularly important in rapidly changing environments: adaptive phenotypic plasticity and/or bet hedging. Adaptive plasticity could enable individuals to match their phenotypes to the expected environment if there is an accurate cue predicting the selective environment. Diversifying bet hedging involves the production of seemingly random phenotypes in an unpredictable environment, some of which may be adaptive. Here, I review the central role of the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoids (GCs) in enabling vertebrates to cope with environmental change through adaptive plasticity and bet hedging. I first describe how the HPA axis mediates three types of adaptive plasticity to cope with environmental change (evasion, tolerance, recovery) over short timescales (e.g., 1-3 generations) before discussing how the implications of GCs on phenotype integration may depend upon the timescale under consideration. GCs can promote adaptive phenotypic integration, but their effects on phenotypic co-variation could also limit the dimensions of phenotypic space explored by animals over longer timescales. Finally, I discuss how organismal responses to environmental stressors can act as a bet hedging mechanism and therefore enhance evolvability by increasing genetic or phenotypic variability or reducing patterns of genetic and phenotypic co-variance. Together, this emphasizes the crucial role of the HPA axis in understanding fundamental questions in evolutionary ecology.
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Affiliation(s)
- Ben Dantzer
- Department of Psychology, University of Michigan, MI 48109 Ann Arbor, MI, USA; Department of Ecology and Evolutionary Biology, University of Michigan, MI 48109, Ann Arbor, MI, USA.
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6
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Hau M, Deimel C, Moiron M. Great tits differ in glucocorticoid plasticity in response to spring temperature. Proc Biol Sci 2022; 289:20221235. [PMID: 36350212 PMCID: PMC9653245 DOI: 10.1098/rspb.2022.1235] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 10/14/2022] [Indexed: 09/05/2023] Open
Abstract
Fluctuations in environmental temperature affect energy metabolism and stimulate the expression of reversible phenotypic plasticity in vertebrate behavioural and physiological traits. Changes in circulating concentrations of glucocorticoid hormones often underpin environmentally induced phenotypic plasticity. Ongoing climate change is predicted to increase fluctuations in environmental temperature globally, making it imperative to determine the standing phenotypic variation in glucocorticoid responses of free-living populations to evaluate their potential for coping via plastic or evolutionary changes. Using a reaction norm approach, we repeatedly sampled wild great tit (Parus major) individuals for circulating glucocorticoid concentrations during reproduction across five years to quantify individual variation in glucocorticoid plasticity along an environmental temperature gradient. As expected, baseline and stress-induced glucocorticoid concentrations increased with lower environmental temperatures at the population and within-individual level. Moreover, we provide unique evidence that individuals differ significantly in their plastic responses to the temperature gradient for both glucocorticoid traits, with some displaying greater plasticity than others. Average concentrations and degree of plasticity covaried for baseline glucocorticoids, indicating that these two reaction norm components are linked. Hence, individual variation in glucocorticoid plasticity in response to a key environmental factor exists in a wild vertebrate population, representing a crucial step to assess their potential to endure temperature fluctuations.
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Affiliation(s)
- Michaela Hau
- Max Planck Institute for Ornithology, Seewiesen, Germany
- University of Konstanz, Konstanz, Germany
| | | | - Maria Moiron
- Institute of Avian Research, Wilhelmshaven, Germany
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7
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Petrullo L, Delaney D, Boutin S, McAdam AG, Lane JE, Boonstra R, Palme R, Dantzer B. The glucocorticoid response to environmental change is not specific to agents of natural selection in wild red squirrels. Horm Behav 2022; 146:105262. [PMID: 36191397 DOI: 10.1016/j.yhbeh.2022.105262] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 08/30/2022] [Accepted: 09/07/2022] [Indexed: 11/04/2022]
Abstract
Evolutionary endocrinology aims to understand how natural selection shapes endocrine systems and the degree to which endocrine systems themselves can induce phenotypic responses to environmental changes. Such responses may be specialized in that they reflect past selection for responsiveness only to those ecological factors that ultimately influence natural selection. Alternatively, endocrine responses may be broad and generalized, allowing organisms to cope with a variety of environmental changes simultaneously. Here, we empirically tested whether the endocrine response of female North American red squirrels (Tamiasciurus hudsonicus) was specialized or generalized. We first quantified the direction and magnitude of natural selection acting on three female life history traits (parturition date, litter size, offspring postnatal growth rate) during 32 years of fluctuations in four potential ecological agents of selection (food availability, conspecific density, predator abundance, and temperature). Only three of the four variables (food, density, and predators) affected patterns of natural selection on female life history traits. We then quantified fecal glucocorticoid metabolites (FGMs) across 7 years and found that all four environmental variables, regardless of their effects on patterns of selection, were associated with glucocorticoid production. Our results provide support for a generalized, rather than specific, glucocorticoid response to environmental change that can integrate across multiple co-occurring environmental stressors.
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Affiliation(s)
- Lauren Petrullo
- Department of Psychology, University of Michigan, Ann Arbor, MI 48108, USA.
| | - David Delaney
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA
| | - Stan Boutin
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
| | - Andrew G McAdam
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA
| | - Jeffrey E Lane
- Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
| | - Rudy Boonstra
- Department of Biological Sciences, Centre for the Neurobiology of Stress, University of Toronto Scarborough, Toronto, ON M1C 1A6, Canada
| | - Rupert Palme
- Unit of Physiology, Pathophysiology and Experimental Endocrinology, Department of Biomedical Sciences, University of Veterinary Medicine Vienna, Veterina ̈rplatz 1, Vienna 1210, Austria
| | - Ben Dantzer
- Department of Psychology, University of Michigan, Ann Arbor, MI 48108, USA; Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48108, USA
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8
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Santicchia F, Wauters LA, Dantzer B, Palme R, Tranquillo C, Preatoni D, Martinoli A. Native species exhibit physiological habituation to invaders: a reason for hope. Proc Biol Sci 2022; 289:20221022. [PMID: 36168765 PMCID: PMC9515632 DOI: 10.1098/rspb.2022.1022] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 09/05/2022] [Indexed: 11/12/2022] Open
Abstract
Animals cope with environmental perturbations through the stress response, a set of behavioural and physiological responses aimed to maintain and/or return to homeostasis and enhance fitness. Vertebrate neuroendocrine axis activation in response to environmental stressors can result in the secretion of glucocorticoids (GCs), whose acute increases may be adaptive, while chronic elevation may be detrimental. Invasive grey squirrels (Sciurus carolinensis) act as a stressor eliciting elevation of GCs in native red squirrels (Sciurus vulgaris). Here we used 6-year data of variation in faecal glucocorticoid metabolite (FGM) concentrations following invasion by grey squirrels in three red squirrel populations, to identify if red squirrels showed physiological habituation to this stressor. The decrease in FGMs over time was more pronounced shortly after invasion and at high densities of grey squirrels while it decreased less strongly and was no longer influenced by the invader density as time since invasion elapsed. At the individual level, FGMs also decreased more markedly as each red squirrel experienced prolonged contact with the invader. Our study provides compelling new data suggesting that native species in the wild can habituate to prolonged contact with invasive species, showing that they may avoid the potentially harmful effects of chronic elevations in GCs.
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Affiliation(s)
- Francesca Santicchia
- Environment Analysis and Management Unit - Guido Tosi Research Group - Department of Theoretical and Applied Sciences, Università degli Studi dell'Insubria, via J. H. Dunant 3, 21100 Varese, Italy
| | - Lucas Armand Wauters
- Environment Analysis and Management Unit - Guido Tosi Research Group - Department of Theoretical and Applied Sciences, Università degli Studi dell'Insubria, via J. H. Dunant 3, 21100 Varese, Italy
- Evolutionary Ecology Group, Department of Biology, University of Antwerp, Campus Drie Eiken Universiteitsplein 1, 2610 Wilrijk, Belgium
| | - Ben Dantzer
- Department of Psychology, University of Michigan, 530 Church Street, Ann Arbor, MI, 48109, USA
- Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University, Ann Arbor, MI 48109, USA
| | - Rupert Palme
- Unit of Physiology, Pathophysiology and Experimental Endocrinology, Department of Biomedical Sciences, University of Veterinary Medicine Vienna, Veterinärplatz 1, 1210 Vienna, Austria
| | - Claudia Tranquillo
- Environment Analysis and Management Unit - Guido Tosi Research Group - Department of Theoretical and Applied Sciences, Università degli Studi dell'Insubria, via J. H. Dunant 3, 21100 Varese, Italy
| | - Damiano Preatoni
- Environment Analysis and Management Unit - Guido Tosi Research Group - Department of Theoretical and Applied Sciences, Università degli Studi dell'Insubria, via J. H. Dunant 3, 21100 Varese, Italy
| | - Adriano Martinoli
- Evolutionary Ecology Group, Department of Biology, University of Antwerp, Campus Drie Eiken Universiteitsplein 1, 2610 Wilrijk, Belgium
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9
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Cockrem JF. Individual variation, personality, and the ability of animals to cope with climate change. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.897314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The Sixth Assessment of the Intergovernmental Panel on Climate Change describes negative effects of climate change on animals occurring on a larger scale than previously appreciated. Animal species are increasingly experiencing more frequent and extreme weather in comparison with conditions in which the species evolved. Individual variation in behavioural and physiological responses of animals to stimuli from the environment is ubiquitous across all species. Populations with relatively high levels of individual variation are more likely to be able to survive in a range of environmental conditions and cope with climate change than populations with low levels of variation. Behavioural and physiological responses are linked in animals, and personality can be defined as consistent individual behavioural and physiological responses of animals to changes in their immediate environment. Glucocorticoids (cortisol and corticosterone) are hormones that, in addition to metabolic roles, are released when the neuroendocrine stress system is activated in response to stimuli from the environment perceived to be threatening. The size of a glucocorticoid response of an animal is an indication of the animal’s personality. Animals with reactive personalities have relatively high glucocorticoid responses, are relatively slow and thorough to explore new situations, and are more flexible and able to cope with changing or unpredictable conditions than animals with proactive personalities. Animals with reactive personalities are likely to be better able to cope with environmental changes due to climate change than animals with proactive personalities. A reaction norm shows the relationship between phenotype and environmental conditions, with the slope of a reaction norm for an individual animal a measure of phenotypic plasticity. If reaction norm slopes are not parallel, there is individual variation in plasticity. Populations with relatively high individual variation in plasticity of reaction norms will have more animals that can adjust to a new situation than populations with little variation in plasticity, so are more likely to persist as environments change due to climate change. Future studies of individual variation in plasticity of responses to changing environments will help understanding of how populations of animals may be able to cope with climate change.
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10
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Dantzer B, Newman AEM. Expanding the frame around social dynamics and glucocorticoids: From hierarchies within the nest to competitive interactions among species. Horm Behav 2022; 144:105204. [PMID: 35689971 DOI: 10.1016/j.yhbeh.2022.105204] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 05/10/2022] [Accepted: 05/18/2022] [Indexed: 11/25/2022]
Abstract
The effect of the social environment on individual state or condition has largely focused on glucocorticoid levels (GCs). As metabolic hormones whose production can be influenced by nutritional, physical, or psychosocial stressors, GCs are a valuable (though singular) measure that may reflect the degree of "stress" experienced by an individual. Most work to date has focused on how social rank influences GCs in group-living species or how predation risk influences GCs in prey. This work has been revealing, but a more comprehensive assessment of the social environment is needed to fully understand how different features of the social environment influence GCs in both group living and non-group living species and across life history stages. Just as there can be intense within-group competition among adult conspecifics, it bears appreciating there can also be competition among siblings from the same brood, among adult conspecifics that do not live in groups, or among heterospecifics. In these situations, dominance hierarchies typically emerge, albeit, do dominants or subordinate individuals or species have higher GCs? We examine the degree of support for hypotheses derived from group-living species about whether differential GCs between dominants and subordinates reflect the "stress of subordination" or "costs of dominance" in these other social contexts. By doing so, we aim to test the generality of these two hypotheses and propose new research directions to broaden the lens that focuses on social hierarchies and GCs.
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Affiliation(s)
- Ben Dantzer
- Department of Psychology, University of Michigan, 48109 Ann Arbor, MI, USA; Department of Ecology and Evolutionary Biology, University of Michigan, 48109, Ann Arbor, MI, USA.
| | - Amy E M Newman
- Department of Integrative Biology, University of Guelph, Guelph, ON N1G2W1, Canada
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11
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Grindstaff JL, Beaty LE, Ambardar M, Luttbeg B. Integrating theoretical and empirical approaches for a robust understanding of endocrine flexibility. J Exp Biol 2022; 225:274311. [PMID: 35258612 PMCID: PMC8987727 DOI: 10.1242/jeb.243408] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
There is growing interest in studying hormones beyond single 'snapshot' measurements, as recognition that individual variation in the endocrine response to environmental change may underlie many rapid, coordinated phenotypic changes. Repeated measures of hormone levels in individuals provide additional insight into individual variation in endocrine flexibility - that is, how individuals modulate hormone levels in response to the environment. The ability to quickly and appropriately modify phenotype is predicted to be favored by selection, especially in unpredictable environments. The need for repeated samples from individuals can make empirical studies of endocrine flexibility logistically challenging, but methods based in mathematical modeling can provide insights that circumvent these challenges. Our Review introduces and defines endocrine flexibility, reviews existing studies, makes suggestions for future empirical work, and recommends mathematical modeling approaches to complement empirical work and significantly advance our understanding. Mathematical modeling is not yet widely employed in endocrinology, but can be used to identify innovative areas for future research and generate novel predictions for empirical testing.
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Affiliation(s)
| | - Lynne E Beaty
- School of Science, Penn State Erie - The Behrend College, Erie, PA 16563, USA
| | - Medhavi Ambardar
- Department of Biological Sciences, Fort Hays State University, Hays, KS 67601, USA
| | - Barney Luttbeg
- Department of Integrative Biology, Oklahoma State University, OK 74078, USA
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12
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Abstract
The naked mole-rat (Heterocephalus glaber) and the Damaraland mole-rat (Fukomys damarensis) live in large colonies in underground tunnel systems in sub-Saharan Africa. Most members of the colonies are suppressed from reproduction and they are unlikely to reproduce during their lifetime. Only one female and a small number of males reproduce. This extreme cooperative social system has fascinated researchers since the naked mole-rat was first described as eusocial. Despite much research into the mechanisms of social suppression, the exact mechanisms are still unclear. Much evidence points towards high glucocorticoid concentrations caused by agonistic behaviour by the breeding female suppressing reproduction of non-breeders, but laboratory studies have not found any differences in glucocorticoids between breeders and non-breeders. There is, however, considerable evidence from field studies and other social mole-rats that social stress may indeed be an important factor of social suppression in social mole-rats and that those mechanisms are affected by the stability of the colony and environmental conditions. This review aims to provide a summary of the current knowledge of the relationship between environmental conditions, colony stability, glucocorticoids and reproductive suppression in social mole-rat species and suggests some avenues for future research.
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Affiliation(s)
- Katarina Medger
- Department of Biology, University of Kentucky, Lexington, KY, USA
- Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
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13
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Petrullo L, Ren T, Wu M, Boonstra R, Palme R, Boutin S, McAdam AG, Dantzer B. Glucocorticoids coordinate changes in gut microbiome composition in wild North American red squirrels. Sci Rep 2022; 12:2605. [PMID: 35173201 PMCID: PMC8850573 DOI: 10.1038/s41598-022-06359-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Accepted: 01/24/2022] [Indexed: 12/31/2022] Open
Abstract
The gut microbiome impacts host health and fitness, in part through the diversification of gut metabolic function and pathogen protection. Elevations in glucocorticoids (GCs) appear to reduce gut microbiome diversity in experimental studies, suggesting that a loss of microbial diversity may be a negative consequence of increased GCs. However, given that ecological factors like food availability and population density may independently influence both GCs and microbial diversity, understanding how these factors structure the GC-microbiome relationship is crucial to interpreting its significance in wild populations. Here, we used an ecological framework to investigate the relationship between GCs and gut microbiome diversity in wild North American red squirrels (Tamiasciurus hudsonicus). As expected, higher GCs predicted lower gut microbiome diversity and an increase in metabolic taxa. Surprisingly, but in line with prior empirical studies on wild animals, gastrointestinal pathogens decreased as GCs increased. Both dietary heterogeneity and an upcoming food pulse exhibited direct effects on gut microbiome diversity, whereas conspecific density and reproductive activity impacted diversity indirectly via changes in host GCs. Our results provide evidence of a gut-brain axis in wild red squirrels and highlight the importance of situating the GC-gut microbiome relationship within an ecological framework.
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Affiliation(s)
- Lauren Petrullo
- Department of Psychology, University of Michigan, Ann Arbor, MI, 48108, USA.
| | - Tiantian Ren
- Department of Biology, University of Virginia, Charlottesville, VA, 22904, USA
| | - Martin Wu
- Department of Biology, University of Virginia, Charlottesville, VA, 22904, USA
| | - Rudy Boonstra
- Department of Biological Sciences, Centre for the Neurobiology of Stress, University of Toronto Scarborough, Toronto, ON, M1C 1A6, Canada
| | - Rupert Palme
- Unit of Physiology, Pathophysiology and Experimental Endocrinology, Department of Biomedical Sciences, University of Veterinary Medicine Vienna, Veterina ̈rplatz 1, 1210, Vienna, Austria
| | - Stan Boutin
- Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada
| | - Andrew G McAdam
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
| | - Ben Dantzer
- Department of Psychology, University of Michigan, Ann Arbor, MI, 48108, USA.
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48108, USA.
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14
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Dantzer B, Boutin S, Lane JE, McAdam AG. Integrative Studies of the Effects of Mothers on Offspring: An Example from Wild North American Red Squirrels. ADVANCES IN NEUROBIOLOGY 2022; 27:269-296. [PMID: 36169819 DOI: 10.1007/978-3-030-97762-7_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Animal species vary in whether they provide parental care or the type of care provided, and this variation in parental care among species has been a common focus of comparative studies. However, the proximate causes and ultimate consequences of within-species variation in parental care have been less studied. Most studies about the impacts of within-species variation in parental care on parental fitness have been in primates, whereas studies in laboratory rodents have been invaluable for understanding what causes inter-individual variation in parental care and its influence on offspring characteristics. We integrated both of these perspectives in our long-term study of North American red squirrels (Tamiasciurus hudsonicus) in the Yukon, Canada, where we have focused on understanding the impacts of mothers on offspring. This includes documenting the impacts that mothers or the maternal environment itself has on their offspring, identifying how changes in maternal physiology impact offspring characteristics, the presence of individual variation in maternal attentiveness toward offspring before weaning and its fitness consequences, and postweaning maternal care and its fitness consequences. We provide an overview of these contributions to understanding the impacts mothers have on their offspring in red squirrels using an integrative framework and contrast them with studies in the laboratory.
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Affiliation(s)
- Ben Dantzer
- Department of Psychology, University of Michigan, Ann Arbor, MI, USA.
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
| | - Stan Boutin
- Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Jeffrey E Lane
- Department of Biology, University of Saskatchewan, Saskatoon, SK, Canada
| | - Andrew G McAdam
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
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15
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Predicting the individual identity of non-invasive faecal and hair samples using biotelemetry clusters. Mamm Biol 2021. [DOI: 10.1007/s42991-021-00173-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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16
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Malkoc K, Mentesana L, Casagrande S, Hau M. Quantifying Glucocorticoid Plasticity Using Reaction Norm Approaches: There Still is So Much to Discover! Integr Comp Biol 2021; 62:58-70. [PMID: 34665256 PMCID: PMC9375136 DOI: 10.1093/icb/icab196] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Hormones are highly responsive internal signals that help organisms adjust their phenotype to fluctuations in environmental and internal conditions. Our knowledge of the causes and consequences of variation in circulating hormone concentrations has improved greatly in the past. However, this knowledge often comes from population-level studies, which generally tend to make the flawed assumption that all individuals respond in the same way to environmental changes. Here, we advocate that we can vastly expand our understanding of the ecology and evolution of hormonal traits once we acknowledge the existence of individual differences by quantifying hormonal plasticity at the individual level, where selection acts. In this review, we use glucocorticoid (GC) hormones as examples of highly plastic endocrine traits that interact intimately with energy metabolism but also with other organismal traits like behavior and physiology. First, we highlight the insights gained by repeatedly assessing an individual's GC concentrations along a gradient of environmental or internal conditions using a “reaction norm approach.” This study design should be followed by a hierarchical statistical partitioning of the total endocrine variance into the among-individual component (individual differences in average hormone concentrations, i.e., in the intercept of the reaction norm) and the residual (within-individual) component. The latter is ideally further partitioned by estimating more precisely hormonal plasticity (i.e., the slope of the reaction norm), which allows to test whether individuals differ in the degree of hormonal change along the gradient. Second, we critically review the published evidence for GC variation, focusing mostly on among- and within-individual levels, finding only a good handful of studies that used repeated-measures designs and random regression statistics to investigate GC plasticity. These studies indicate that individuals can differ in both the intercept and the slope of their GC reaction norm to a known gradient. Third, we suggest rewarding avenues for future work on hormonal reaction norms, for example to uncover potential costs and trade-offs associated with GC plasticity, to test whether GC plasticity varies when an individual's reaction norm is repeatedly assessed along the same gradient, whether reaction norms in GCs covary with those in other traits like behavior and fitness (generating multivariate plasticity), or to quantify GC reaction norms along multiple external and internal gradients that act simultaneously (leading to multidimensional plasticity). Throughout this review, we emphasize the power that reaction norm approaches offer for resolving unanswered questions in ecological and evolutionary endocrinology.
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Affiliation(s)
- Kasja Malkoc
- Research Group for Evolutionary Physiology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Lucia Mentesana
- Research Group for Evolutionary Physiology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Stefania Casagrande
- Research Group for Evolutionary Physiology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Michaela Hau
- Department of Biology, University of Konstanz, Konstanz, Germany
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17
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Malkoc K, Casagrande S, Hau M. Inferring Whole-Organism Metabolic Rate From Red Blood Cells in Birds. Front Physiol 2021; 12:691633. [PMID: 34335298 PMCID: PMC8322697 DOI: 10.3389/fphys.2021.691633] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 06/21/2021] [Indexed: 11/13/2022] Open
Abstract
Metabolic rate is a key ecological variable that quantifies the energy expenditure needed to fuel almost all biological processes in an organism. Metabolic rates are typically measured at the whole-organism level (woMR) with protocols that can elicit stress responses due to handling and confinement, potentially biasing resulting data. Improved, non-stressful methodology would be especially valuable for measures of field metabolic rate, which quantifies the energy expenditure of free-living individuals. Recently, techniques to measure cellular metabolic rate (cMR) in mitochondria of blood cells have become available, suggesting that blood-based cMR can be a proxy of organismal aerobic performance. Aerobic metabolism actually takes place in the mitochondria. Quantifying cMR from blood samples offers several advantages such as direct estimates of metabolism and minimized disturbance of individuals. To our knowledge, the hypothesis that blood-based cMR correlates with woMR has not yet been directly tested. We measured cMR in red blood cells of captive great tits (Parus major), first during their morning activity period and second after subjecting them to a 2.5 h day-time respirometry protocol to quantify woMR. We predicted cMR to decrease as individuals transitioned from an active to a resting state. In the two blood samples we also assessed circulating corticosterone concentrations to determine the perceived disturbance of individuals. From respirometry traces we extracted initial and final woMR measures to test for a predicted positive correlation with cMR measures, while accounting for corticosterone concentrations. Indeed, cMR declined from the first to the second measurement. Furthermore, woMR and cMR were positively related in individuals that had relatively low corticosterone concentrations and displayed little locomotor activity throughout respirometry. By contrast, woMR and cMR covaried negatively in birds that increased corticosterone concentrations and activity levels substantially. Our results show that red blood cell cMR represents a proxy for woMR when birds do not display signs of stress, i.e., either before increases in hormonal or behavioral parameters have occurred or after they have abated. This method represents a valuable tool for obtaining metabolic data repeatedly and in free-living individuals. Our findings also highlight the importance of accounting for individual stress responses when measuring metabolic rate at any level.
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Affiliation(s)
- Kasja Malkoc
- Research Group for Evolutionary Physiology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Stefania Casagrande
- Research Group for Evolutionary Physiology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Michaela Hau
- Research Group for Evolutionary Physiology, Max Planck Institute for Ornithology, Seewiesen, Germany.,Department of Biology, University of Konstanz, Konstanz, Germany
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18
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Baldan D, Negash M, Ouyang JQ. Are individuals consistent? Endocrine reaction norms under different ecological challenges. J Exp Biol 2021; 224:269204. [PMID: 34142697 DOI: 10.1242/jeb.240499] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Accepted: 05/21/2021] [Indexed: 12/29/2022]
Abstract
Quantifying organismal capacity for compensatory mechanisms is essential to forecast responses to environmental change. Despite accumulating evidence for individual variation in physiological plasticity, the causes and consequences of this variation remain unclear. An outstanding question is whether individual reaction norms are consistent across different environmental challenges, i.e. whether an individual that is responsive to one environmental variable will be equally responsive to a different environmental variable. Additionally, are these reaction norms themselves consistent over time, i.e. repeatable? Here, we quantified individual baseline glucocorticoid responses in house sparrows, Passer domesticus, to sequential manipulations of temperature, wind speed and food unpredictability that were repeated in discrete blocks of sampling under both control and stressor-exposed conditions. Individuals significantly decreased their baseline corticosterone levels and increased their mass during treatment exposure. This response was consistent across environmental challenge types. There was high repeatability in the intercept and slope of the baseline corticosterone reaction norm between environmental challenges but broad credible intervals in the repeatability of the reaction norm slope, suggesting that although glucocorticoid levels during baseline conditions are repeatable, among-individual variation in the shape of the glucocorticoid response may be higher than within-individual variation. Within-subject variation in baseline corticosterone levels was mainly explained by within-individual variation in body mass during stressor exposure. Despite the high lability in physiological traits, endocrine plasticity is repeatable across environmental challenges and may be able to evolve as a result of genetic accommodation, in which selection acts on genetic variation of reaction norms.
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Affiliation(s)
- Davide Baldan
- Department of Biology, University of Nevada, Reno, Reno, NV 89557-0314, USA
| | - Mekail Negash
- Department of Biology, University of Nevada, Reno, Reno, NV 89557-0314, USA
| | - Jenny Q Ouyang
- Department of Biology, University of Nevada, Reno, Reno, NV 89557-0314, USA
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19
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Westrick SE, van Kesteren F, Boutin S, Lane JE, McAdam AG, Dantzer B. Maternal glucocorticoids have minimal effects on HPA axis activity and behavior of juvenile wild North American red squirrels. J Exp Biol 2021; 224:jeb.236620. [PMID: 33795416 DOI: 10.1242/jeb.236620] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 03/29/2021] [Indexed: 12/27/2022]
Abstract
As a response to environmental cues, maternal glucocorticoids (GCs) may trigger adaptive developmental plasticity in the physiology and behavior of offspring. In North American red squirrels (Tamiasciurus hudsonicus), mothers exhibit increased GCs when conspecific density is elevated, and selection favors more aggressive and perhaps more active mothers under these conditions. We tested the hypothesis that elevated maternal GCs cause shifts in offspring behavior that may prepare them for high-density conditions. We experimentally elevated maternal GCs during gestation or early lactation. We measured two behavioral traits (activity and aggression) in weaned offspring using standardized behavioral assays. Because maternal GCs may influence offspring hypothalamic-pituitary-adrenal (HPA) axis dynamics, which may in turn affect behavior, we also measured the impact of our treatments on offspring HPA axis dynamics (adrenal reactivity and negative feedback), and the association between offspring HPA axis dynamics and behavior. Increased maternal GCs during lactation, but not gestation, slightly elevated activity levels in offspring. Offspring aggression and adrenal reactivity did not differ between treatment groups. Male, but not female, offspring from mothers treated with GCs during pregnancy exhibited stronger negative feedback compared with those from control mothers, but there were no differences in negative feedback between lactation treatment groups. Offspring with higher adrenal reactivity from mothers treated during pregnancy (both controls and GC-treated) exhibited lower aggression and activity. These results suggest that maternal GCs during gestation or early lactation alone may not be a sufficient cue to produce substantial changes in behavioral and physiological stress responses in offspring in natural populations.
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Affiliation(s)
- Sarah E Westrick
- Department of Psychology, University of Michigan, Ann Arbor, MI48109-1043, USA
| | - Freya van Kesteren
- Department of Psychology, University of Michigan, Ann Arbor, MI48109-1043, USA
| | - Stan Boutin
- Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2E9
| | - Jeffrey E Lane
- Department of Biology, University of Saskatchewan, Saskatoon, SK, Canada, S7N 5E2
| | - Andrew G McAdam
- Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309-0334, USA
| | - Ben Dantzer
- Department of Psychology, University of Michigan, Ann Arbor, MI48109-1043, USA.,Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109-1085, USA
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20
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Century-long cod otolith biochronology reveals individual growth plasticity in response to temperature. Sci Rep 2020; 10:16708. [PMID: 33028859 PMCID: PMC7541619 DOI: 10.1038/s41598-020-73652-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Accepted: 09/21/2020] [Indexed: 11/08/2022] Open
Abstract
Otolith biochronologies combine growth records from individual fish to produce long-term growth sequences, which can help to disentangle individual from population-level responses to environmental variability. This study assessed individual thermal plasticity of Atlantic cod (Gadus morhua) growth in Icelandic waters based on measurements of otolith increments. We applied linear mixed-effects models and developed a century-long growth biochronology (1908-2014). We demonstrated interannual and cohort-specific changes in the growth of Icelandic cod over the last century which were mainly driven by temperature variation. Temperature had contrasting relationships with growth-positive for the fish during the youngest ages and negative during the oldest ages. We decomposed the effects of temperature on growth observed at the population level into within-individual effects and among-individual effects and detected significant individual variation in the thermal plasticity of growth. Variance in the individual plasticity differed across cohorts and may be related to the mean environmental conditions experienced by the group. Our results underscore the complexity of the relationships between climatic conditions and the growth of fish at both the population and individual level, and highlight the need to distinguish between average population responses and growth plasticity of the individuals for accurate growth predictions.
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21
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Guindre-Parker S. Individual Variation in Glucocorticoid Plasticity: Considerations and Future Directions. Integr Comp Biol 2020; 60:79-88. [DOI: 10.1093/icb/icaa003] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Abstract
The hypothalamic–pituitary–adrenal (HPA) axis regulates the secretion of glucocorticoids, hormones with diverse roles ranging from regulating daily metabolic demand to coping with sudden perturbations. As a result, glucocorticoids are thought to help vertebrates track their changing environments and coordinate plasticity in diverse phenotypes. While this endocrine system is highly plastic—where one individual can produce multiple phenotypes across varying environmental conditions—little is understood about the degree to which individuals, populations, or species differ in circulating glucocorticoid plasticity. Empirical research quantifying individual variation in glucocorticoid plasticity has increased in recent years, though the multiple complex roles of the HPA-axis make it challenging to generalize the extent to which individual variation in plasticity exists. I provide an overview of current findings on variation in glucocorticoids plasticity, and outline multiple types of glucocorticoid plasticity researchers should consider in future work to advance our understanding of the causes and consequences of individual variation in glucocorticoid plasticity.
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Affiliation(s)
- Sarah Guindre-Parker
- Department of Ecology, Evolution & Organismal Biology, Kennesaw State University, Kennesaw, GA 30144, USA
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22
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Guindre-Parker S, Mcadam AG, van Kesteren F, Palme R, Boonstra R, Boutin S, Lane JE, Dantzer B. Individual variation in phenotypic plasticity of the stress axis. Biol Lett 2019; 15:20190260. [PMID: 31337294 DOI: 10.1098/rsbl.2019.0260] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Phenotypic plasticity-one individual's capacity for phenotypic variation under different environments-is critical for organisms facing fluctuating conditions within their lifetime. North American red squirrels (Tamiasciurus hudsonicus) experience drastic among-year fluctuations in conspecific density. This shapes juvenile competition over vacant territories and overwinter survival. To help young cope with competition at high densities, mothers can increase offspring growth rates via a glucocorticoid-mediated maternal effect. However, this effect is only adaptive under high densities, and faster growth often comes at a cost to longevity. While red squirrels can adjust hormones in response to fluctuating density, the degree to which mothers differ in glucocorticoid plasticity across changing densities remains unknown. Findings from our reaction norm approach revealed significant individual variation not only in a female red squirrel's mean endocrine phenotype but also in endocrine plasticity in response to changes in local density. Future work on proximate and ultimate drivers of variation in endocrine plasticity and maternal effects is needed, particularly in free-living animals experiencing fluctuating environments.
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Affiliation(s)
- Sarah Guindre-Parker
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada.,Department of Psychology, University of Michigan, Ann Arbor, MI, USA
| | - Andrew G Mcadam
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | | | - Rupert Palme
- Department of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria
| | - Rudy Boonstra
- Department of Biological Sciences, University of Toronto Scarborough, Scarborough, Ontario, Canada
| | - Stan Boutin
- Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada
| | - Jeffrey E Lane
- Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Ben Dantzer
- Department of Psychology, University of Michigan, Ann Arbor, MI, USA.,Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA
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