1
|
Mahr K, Anzengruber M, Hellerschmid A, Slezacek J, Hoi H, Subbiahdoss G, Gabor F, Lendvai ÁZ. Biocompatible polymeric microparticles serve as novel and reliable vehicles for exogenous hormone manipulations in passerines. Gen Comp Endocrinol 2023; 336:114234. [PMID: 36791824 DOI: 10.1016/j.ygcen.2023.114234] [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: 07/14/2022] [Revised: 02/02/2023] [Accepted: 02/09/2023] [Indexed: 02/15/2023]
Abstract
The administration of exogenous hormones emerged as an essential tool for field studies in endocrinology. However, working with wild animals remains challenging, because under field conditions not every available method meets the necessary requirements. Achieving a sustained elevation in hormone levels, while simultaneously minimising handling time and invasiveness of the procedure is a difficult task in field endocrinology. Facing this challenge, we have investigated the suitability of biocompatible polymeric microparticles, a novel method for drug-administration, as a tool to manipulate hormones in small songbirds. We chose the insulin-like growth factor-1 (IGF-1) as target hormone, because it receives great interest from the research community due to its important role in shaping life-history traits. Moreover, its short half-life and hydrophilic properties imply a major challenge in finding a suitable method to achieve a sustained, systemic long-term release. To study the release kinetics, we injected either IGF-1 loaded polylactic-co-glycolic acid (PLGA) microparticles or dispersion medium (control group) in the skin pocket of the interscapular region of captive bearded reedlings (Panurus biarmicus). We collected blood samples for 7 consecutive days plus an additional sampling period after two weeks and complemented these with an in vitro experiment. Our results show that in vitro, PLGA microparticles allowed a stable IGF-1 release for more than 15 days, following a burst release at the beginning of the measurement. In vivo, the initial burst was followed by a drop to still elevated levels in circulating IGF-1 until the effect vanished by 16 days post-treatment. This study is the first to describe the use of PLGA-microparticles as a novel tool for exogenous hormone administration in a small passerine. We suggest that this method is highly suitable to achieve the systemic long-term release of hydrophilic hormones with short half-life and reduces overall handling time, as it requires only one subcutaneous injection.
Collapse
Affiliation(s)
- Katharina Mahr
- Konrad Lorenz Institute of Ethology, Department of Interdisciplinary Life Sciences, University of Veterinary Medicine, Vienna, Austria.
| | - Maria Anzengruber
- Department of Pharmaceutical Sciences, Division of Pharmaceutical Technology and Biopharmaceutics, University of Vienna, Austria
| | - Anna Hellerschmid
- Konrad Lorenz Institute of Ethology, Department of Interdisciplinary Life Sciences, University of Veterinary Medicine, Vienna, Austria
| | - Julia Slezacek
- Konrad Lorenz Institute of Ethology, Department of Interdisciplinary Life Sciences, University of Veterinary Medicine, Vienna, Austria
| | - Herbert Hoi
- Konrad Lorenz Institute of Ethology, Department of Interdisciplinary Life Sciences, University of Veterinary Medicine, Vienna, Austria
| | - Guruprakash Subbiahdoss
- Institute of Biologically Inspired Materials, Department of Nanobiotechnology, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria
| | - Franz Gabor
- Department of Pharmaceutical Sciences, Division of Pharmaceutical Technology and Biopharmaceutics, University of Vienna, Austria
| | - Ádám Z Lendvai
- Department of Evolutionary Zoology and Human Biology, University of Debrecen, 4032 Debrecen, Hungary
| |
Collapse
|
2
|
Lee DS, Knittel T, Deschner T, Heistermann M, Higham JP. Testing the role of testosterone versus estrogens in mediating reproductive transitions in female rhesus macaques. Horm Behav 2022; 139:105123. [PMID: 35149292 DOI: 10.1016/j.yhbeh.2022.105123] [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: 10/07/2021] [Revised: 01/11/2022] [Accepted: 01/20/2022] [Indexed: 11/16/2022]
Abstract
In male vertebrates, testosterone is generally known to coordinate reproductive trade-offs, in part by promoting the transition to the next reproduction at the expense of current parental care. The role of testosterone in reproductive transitions has been little tested in female vertebrates, especially in mammals. The present study sought to fill this gap, by first undertaking an experimental study, in which we identified DHT, androstenediol, and in particular etiocholanolone, as fecal androgen metabolites which reflect serum testosterone concentration in female rhesus macaques (Macaca mulatta). Using concentrations of fecal etiocholanolone as proxy for circulating testosterone, we then conducted a field study on 46 free-ranging rhesus macaques of Cayo Santiago, Puerto Rico, to test if testosterone mediates the trade-off between reproductive transition (a higher chance of reproducing in the next year) and current reproduction (providing more care to current offspring). While the evidence for testosterone was weak, the testing of fecal immunoreactive estrogen metabolites suggested a potential role of estrogen in reproductive trade-offs. We found large individual differences in fecal etiocholanolone concentrations during the early postpartum period that were unexplained even after accounting for sociodemographic factors such as age and dominance rank. Further investigation is needed to understand this variation. Our study suggests that the actions of testosterone in females may not have evolved to fulfil the same role in primate reproductive transitions as it does in males, and we encourage more studies to consider the function of testosterone in reproductive behaviors and life history transitions in females of mammalian taxa.
Collapse
Affiliation(s)
- D Susie Lee
- Department of Anthropology, New York University, 25 Waverly Place, New York 10003, NY, USA; New York Consortium in Evolutionary Primatology, New York 10024, NY, USA.
| | - Tina Knittel
- Max Planck Institute for Evolutionary Anthropology, Interim Group Primatology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Tobias Deschner
- Max Planck Institute for Evolutionary Anthropology, Interim Group Primatology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Michael Heistermann
- Endocrinology Laboratory, German Primate Center, Leibniz Institute for Primate Research, Kellnerweg 4, 37077 Göttingen, Germany
| | - James P Higham
- Department of Anthropology, New York University, 25 Waverly Place, New York 10003, NY, USA; New York Consortium in Evolutionary Primatology, New York 10024, NY, USA
| |
Collapse
|
3
|
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: 5.0] [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.
Collapse
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
| |
Collapse
|
4
|
Moore IT, Vernasco BJ, Escallón C, Small TW, Ryder TB, Horton BM. Tales of testosterone: Advancing our understanding of environmental endocrinology through studies of neotropical birds. Gen Comp Endocrinol 2019; 273:184-191. [PMID: 29990493 DOI: 10.1016/j.ygcen.2018.07.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 06/21/2018] [Accepted: 07/06/2018] [Indexed: 01/29/2023]
Abstract
Studies of birds have greatly advanced our understanding of how testosterone modulates complex phenotypes, specifically its role in mediating male reproductive and associated behaviors. Yet most of the foundational studies have been limited to northern latitude breeding species despite the fact that they represent only a small fraction of worldwide avian diversity. In contrast, phylogenetic, life-history, and mating system diversity all reach their apex in neotropical avifauna and yet these birds, along with more southern latitude species, remain very poorly understood from an endocrine perspective. Despite the relatively limited previous work on taxa breeding in Central and South America, empirical findings have had a disproportionately large impact on our understanding of testosterone's role in everything from geographic variation to behavioral roles and neuroplasticity. Here, we synthesize how studies of neotropical breeding avifauna have advanced our understanding of how testosterone's actions can and are associated with the broad patterns of phenotypic diversity that we see in birds. In addition, we outline how these studies can be used individually or in a comparative context to address fundamental questions about the environmental endocrinology of testosterone and to understand the diversity of roles that testosterone plays in mediating behavioral variation, reproductive strategies, and associated life-history trade-offs.
Collapse
Affiliation(s)
- I T Moore
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA.
| | - B J Vernasco
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA
| | - C Escallón
- Departamento de Ciencias Básicas, Universidad de la Salle, Cra 2 No. 10-70, Bogotá, Colombia
| | - T W Small
- Department of Biology, University of Memphis, Memphis, TN 38152, USA
| | - T B Ryder
- Migratory Bird Center, Smithsonian Conservation Biology Institute, National Zoological Park, PO Box 37012, MRC 5503, Washington DC 20013, USA
| | - B M Horton
- Department of Biology, Millersville University of Pennsylvania, Millersville, PA 17551, USA
| |
Collapse
|
5
|
Huber N, Fusani L, Ferretti A, Mahr K, Canoine V. Measuring short-term stress in birds: Comparing different endpoints of the endocrine-immune interface. Physiol Behav 2017; 182:46-53. [DOI: 10.1016/j.physbeh.2017.09.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Revised: 09/11/2017] [Accepted: 09/18/2017] [Indexed: 01/10/2023]
|
6
|
Assis VR, Monteiro Titon SC, Teixeira Queiroz-Hazarbassanov NG, de Oliveira Massoco C, Ribeiro Gomes F. Corticosterone transdermal application in toads (Rhinella icterica): Effects on cellular and humoral immunity and steroid plasma levels. JOURNAL OF EXPERIMENTAL ZOOLOGY PART 2017; 327:200-213. [DOI: 10.1002/jez.2093] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 08/02/2017] [Accepted: 08/03/2017] [Indexed: 11/05/2022]
Affiliation(s)
- Vania Regina Assis
- Departamento de Fisiologia; Instituto de Biociências; Universidade de São Paulo; Rua do Matão; São Paulo Brazil
| | | | | | - Cristina de Oliveira Massoco
- Departamento de Patologia; Faculdade de Medicina Veterinária e Zootecnia; Universidade de São Paulo; São Paulo Brazil
| | - Fernando Ribeiro Gomes
- Departamento de Fisiologia; Instituto de Biociências; Universidade de São Paulo; Rua do Matão; São Paulo Brazil
| |
Collapse
|
7
|
Nguyen N, Lee LM, Fashing PJ, Nurmi NO, Stewart KM, Turner TJ, Barry TS, Callingham KR, Goodale CB, Kellogg BS, Burke RJ, Bechtold EK, Claase MJ, Eriksen GA, Jones SC, Kerby JT, Kraus JB, Miller CM, Trew TH, Zhao Y, Beierschmitt EC, Ramsay MS, Reynolds JD, Venkataraman VV. Comparative primate obstetrics: Observations of 15 diurnal births in wild gelada monkeys (Theropithecus gelada) and their implications for understanding human and nonhuman primate birth evolution. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2017; 163:14-29. [DOI: 10.1002/ajpa.23141] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 11/11/2016] [Accepted: 11/21/2016] [Indexed: 11/11/2022]
Affiliation(s)
- Nga Nguyen
- Department of Anthropology & Environmental Studies Program; California State University, Fullerton; Fullerton California
- Centre for Ecological and Evolutionary Synthesis (CEES); Department of Biosciences, University of Oslo; Oslo Norway
| | - Laura M. Lee
- School of Veterinary Medicine; University of Wisconsin; Madison Wisconsin
| | - Peter J. Fashing
- Department of Anthropology & Environmental Studies Program; California State University, Fullerton; Fullerton California
- Centre for Ecological and Evolutionary Synthesis (CEES); Department of Biosciences, University of Oslo; Oslo Norway
| | - Niina O. Nurmi
- Department of Behavioral Ecology; Johann-Friedrich-Blumenbach Institute for Zoology and Anthropology, University of Göttingen; Göttingen Germany
| | | | | | | | | | - C. Barret Goodale
- School of Natural Resources and Extension; University of Alaska Fairbanks; Fairbanks Alaska
| | | | - Ryan J. Burke
- Department of Zoology; University of Oxford; Oxford England, UK
| | - Emily K. Bechtold
- Department of Microbiology; University of Massachusetts; Amherst Massachusetts
| | - Megan J. Claase
- Windy Ridge, Spring Hill, Little Staughton, Bedford; Bedfordshire England, UK
| | - G. Anita Eriksen
- Centre for Ecological and Evolutionary Synthesis (CEES); Department of Biosciences, University of Oslo; Oslo Norway
| | - Sorrel C.Z. Jones
- School of Biological Sciences; Royal Holloway, University of London; England, UK
| | - Jeffrey T. Kerby
- Department of Biological Sciences; Dartmouth College; Hanover New Hampshire
| | - Jacob B. Kraus
- Smithsonian Conservation Biology Institute; Front Royal Virginia
| | - Carrie M. Miller
- Department of Anthropology; University of Minnesota; Minneapolis Minnesota
| | | | - Yi Zhao
- Environmental Studies Program California State University Fullerton; Fullerton California
| | - Evan C. Beierschmitt
- Department of Anthropology; University of California, Santa Barbara; Santa Barbara California
| | - Malcolm S. Ramsay
- Department of Anthropology; University of Toronto; Toronto Ontario Canada
| | | | - Vivek V. Venkataraman
- Department of Human Evolutionary Biology; Harvard University; Cambridge Massachusetts
| |
Collapse
|
8
|
Dantzer B, Westrick SE, van Kesteren F. Relationships between Endocrine Traits and Life Histories in Wild Animals: Insights, Problems, and Potential Pitfalls. Integr Comp Biol 2016; 56:185-97. [DOI: 10.1093/icb/icw051] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
|
9
|
delBarco-Trillo J, Greene LK, Goncalves IB, Fenkes M, Wisse JH, Drewe JA, Manser MB, Clutton-Brock T, Drea CM. Beyond aggression: Androgen-receptor blockade modulates social interaction in wild meerkats. Horm Behav 2016; 78:95-106. [PMID: 26545817 DOI: 10.1016/j.yhbeh.2015.11.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2015] [Revised: 11/01/2015] [Accepted: 11/02/2015] [Indexed: 01/26/2023]
Abstract
In male vertebrates, androgens are inextricably linked to reproduction, social dominance, and aggression, often at the cost of paternal investment or prosociality. Testosterone is invoked to explain rank-related reproductive differences, but its role within a status class, particularly among subordinates, is underappreciated. Recent evidence, especially for monogamous and cooperatively breeding species, suggests broader androgenic mediation of adult social interaction. We explored the actions of androgens in subordinate, male members of a cooperatively breeding species, the meerkat (Suricata suricatta). Although male meerkats show no rank-related testosterone differences, subordinate helpers rarely reproduce. We blocked androgen receptors, in the field, by treating subordinate males with the antiandrogen, flutamide. We monitored androgen concentrations (via baseline serum and time-sequential fecal sampling) and recorded behavior within their groups (via focal observation). Relative to controls, flutamide-treated animals initiated less and received more high-intensity aggression (biting, threatening, feeding competition), engaged in more prosocial behavior (social sniffing, grooming, huddling), and less frequently initiated play or assumed a 'dominant' role during play, revealing significant androgenic effects across a broad range of social behavior. By contrast, guarding or vigilance and measures of olfactory and vocal communication in subordinate males appeared unaffected by flutamide treatment. Thus, androgens in male meerkat helpers are aligned with the traditional trade-off between promoting reproductive and aggressive behavior at a cost to affiliation. Our findings, based on rare endocrine manipulation in wild mammals, show a more pervasive role for androgens in adult social behavior than is often recognized, with possible relevance for understanding tradeoffs in cooperative systems.
Collapse
Affiliation(s)
- Javier delBarco-Trillo
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Department of Evolutionary Anthropology, Duke University, Durham, USA; School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, UK
| | - Lydia K Greene
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Department of Evolutionary Anthropology, Duke University, Durham, USA; University Program in Ecology, Duke University, Durham, USA
| | - Ines Braga Goncalves
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - Miriam Fenkes
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - Jillian H Wisse
- Department of Evolutionary Anthropology, Duke University, Durham, USA
| | - Julian A Drewe
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Royal Veterinary College, University of London, London, UK
| | - Marta B Manser
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland; Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Tim Clutton-Brock
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Mammal Research Institute, University of Pretoria, Pretoria, South Africa; Department of Zoology, University of Cambridge, Cambridge, UK
| | - Christine M Drea
- Kalahari Research Trust, Kuruman River Reserve, Northern Cape, South Africa; Department of Evolutionary Anthropology, Duke University, Durham, USA; University Program in Ecology, Duke University, Durham, USA; Department of Biology, Duke University, Durham, USA.
| |
Collapse
|
10
|
Soldatini C, Albores-Barajas YV, Tagliavia M, Massa B, Fusani L, Canoine V. Effects of human disturbance on cave-nesting seabirds: the case of the storm petrel. CONSERVATION PHYSIOLOGY 2015; 3:cov041. [PMID: 27293726 PMCID: PMC4778440 DOI: 10.1093/conphys/cov041] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 07/30/2015] [Accepted: 08/01/2015] [Indexed: 06/06/2023]
Abstract
Human disturbance is an important stress factor with potentially strong impact on breeding activity in animals. The consequences can be extinction of the breeding population, because disturbed animals might desert their breeding area and find no suitable substitute area. In this study, we investigated the effects of anthropogenic disturbance on a breeding population of Mediterranean storm petrels. Seabirds are increasingly used as bio-indicators for sea environmental parameters, because they are very sensitive to changing conditions. Burrowing or cave-nesting species may be particularly susceptible to human disturbance because their direct contact with humans is usually minimal or absent. First, we compared two different populations (exposed or not exposed to human disturbance) for their individual stress response to a standardized stressor (handling and keeping in a cloth bag). Second, we compared the two sub-colonies for their population-level stress response. Third, we tested experimentally whether sub-colonies of storm petrels exposed to tourism have physiological adaptations to anthropogenic disturbances. Our results indicate that storm petrels may be habituated to moderate disturbance associated with boat traffic close to the colony.
Collapse
Affiliation(s)
- Cecilia Soldatini
- Unidad La Paz, Centro de Investigación Científica y de Educación Superior de Ensenada, Miraflores 334, La Paz, Baja California Sur 23050, Mexico
| | | | - Marcello Tagliavia
- IAMC-CNR (Institute for Coastal Marine Environment), Via del Mare, 3 Torretta Granitola (Campobello di Mazara, TP), 91021, Italy
| | - Bruno Massa
- Department Agriculture and Forest Sciences, University of Palermo, Viale Scienze 13, I-90128 Palermo, Italy
| | - Leonida Fusani
- Department of Behavioural Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria
- Konrad Lorenz Institute for Ethology, University of Veterinary Medicine, Savoyenstrasse 1, 1160 Vienna, Austria
| | - Virginie Canoine
- Department of Behavioural Biology, University of Vienna, Althanstraße 14, 1090 Vienna, Austria
| |
Collapse
|
11
|
Hau M, Goymann W. Endocrine mechanisms, behavioral phenotypes and plasticity: known relationships and open questions. Front Zool 2015; 12 Suppl 1:S7. [PMID: 26816524 PMCID: PMC4722346 DOI: 10.1186/1742-9994-12-s1-s7] [Citation(s) in RCA: 120] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Behavior of wild vertebrate individuals can vary in response to environmental or social factors. Such within-individual behavioral variation is often mediated by hormonal mechanisms. Hormones also serve as a basis for among-individual variations in behavior including animal personalities and the degree of responsiveness to environmental and social stimuli. How do relationships between hormones and behavioral traits evolve to produce such behavioral diversity within and among individuals? Answering questions about evolutionary processes generating among-individual variation requires characterizing how specific hormones are related to variation in specific behavioral traits, whether observed hormonal variation is related to individual fitness and, whether hormonal traits are consistent (repeatable) aspects of an individual's phenotype. With respect to within-individual variation, we need to improve our insight into the nature of the quantitative relationships between hormones and the traits they regulate, which in turn will determine how they may mediate behavioral plasticity of individuals. To address these questions, we review the actions of two steroid hormones, corticosterone and testosterone, in mediating changes in vertebrate behavior, focusing primarily on birds. In the first part, we concentrate on among-individual variation and present examples for how variation in corticosterone concentrations can relate to behaviors such as exploration of novel environments and parental care. We then review studies on correlations between corticosterone variation and fitness, and on the repeatability over time of corticosterone concentrations. At the end of this section, we suggest that further progress in our understanding of evolutionary patterns in the hormonal regulation of behavior may require, as one major tool, reaction norm approaches to characterize hormonal phenotypes as well as their responses to environments. In the second part, we discuss types of quantitative relationships between hormones and behavioral traits within individuals, using testosterone as an example. We review conceptual models for testosterone-behavior relationships and discuss the relevance of these models for within-individual plasticity in behavior. Next, we discuss approaches for testing the nature of quantitative relationships between testosterone and behavior, concluding that again reaction norm approaches might be a fruitful way forward. We propose that an integration of new tools, especially of reaction norm approaches into the field of behavioral endocrinology will allow us to make significant progress in our understanding of the mechanisms, the functional implications and the evolution of hormone–behavior relationships that mediate variation both within and among individuals. This knowledge will be crucial in light of already ongoing habitat alterations due to global change, as it will allow us to evaluate the mechanisms as well as the capacity of wild populations to adjust hormonally-mediated behaviors to altered environmental conditions.
Collapse
Affiliation(s)
- Michaela Hau
- Max Planck Institute for Ornithology, Eberhard-Gwinner-Str., D-82319 Seewiesen, Germany; University of Konstanz, Department of Biology, Universitätsstraße 10, D-78464 Konstanz, Germany
| | - Wolfgang Goymann
- Max Planck Institute for Ornithology, Eberhard-Gwinner-Str., D-82319 Seewiesen, Germany
| |
Collapse
|
12
|
Butler LK, Ries L, Bisson IA, Hayden TJ, Wikelski MM, Romero LM. Opposite but analogous effects of road density on songbirds with contrasting habitat preferences. Anim Conserv 2012. [DOI: 10.1111/j.1469-1795.2012.00576.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- L. K. Butler
- Department of Biology; The College of New Jersey; Ewing; NJ; 08628; USA
| | - L. Ries
- Department of Biology; University of Maryland; College Park; MD; USA
| | - I.-A. Bisson
- Department of Ecology and Evolutionary Biology; Princeton University; Princeton; NJ; USA
| | - T. J. Hayden
- Engineer Research and Development Center; Champaign; IL; USA
| | - M. M. Wikelski
- Department of Ecology and Evolutionary Biology; Princeton University; Princeton; NJ; USA
| | - L. M. Romero
- Department of Biology; The College of New Jersey; Ewing; NJ; 08628; USA
| |
Collapse
|
13
|
Rivers JW, Liebl AL, Owen JC, Martin LB, Betts MG. Baseline corticosterone is positively related to juvenile survival in a migrant passerine bird. Funct Ecol 2012. [DOI: 10.1111/j.1365-2435.2012.02025.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- James W. Rivers
- Department for Forest Ecosystems and Society; Oregon State University; Corvallis; Oregon; 97331; USA
| | - Andrea L. Liebl
- Division of Integrative Biology; University of South Florida; Tampa; Florida; 33620; USA
| | - Jennifer C. Owen
- Department of Fisheries and Wildlife and Department of Large Animal Clinical Sciences; Michigan State University; East Lansing; Michigan; 48824; USA
| | - Lynn B. Martin
- Division of Integrative Biology; University of South Florida; Tampa; Florida; 33620; USA
| | - Matthew G. Betts
- Department for Forest Ecosystems and Society; Oregon State University; Corvallis; Oregon; 97331; USA
| |
Collapse
|
14
|
Nguyen N, Gesquiere L, Alberts SC, Altmann J. Sex differences in the mother–neonate relationship in wild baboons: social, experiential and hormonal correlates. Anim Behav 2012. [DOI: 10.1016/j.anbehav.2012.01.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
|
15
|
Caro SP. Avian ecologists and physiologists have different sexual preferences. Gen Comp Endocrinol 2012; 176:1-8. [PMID: 22222933 DOI: 10.1016/j.ygcen.2011.12.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Revised: 12/16/2011] [Accepted: 12/17/2011] [Indexed: 11/20/2022]
Abstract
Seasonal timing is studied by ecologists and physiologists alike and it is now widely recognized that further integration of these fields is needed for a full understanding of phenology. This is especially true in the light of the impact of global climate change on living organisms. In studies of avian reproduction, one obstacle to this integration is that ecologists and physiologists do not allocate their research efforts equally to males and females. The physiological orchestration of breeding stages has been studied almost exclusively in males, while in avian ecology and evolutionary biology females are more often considered. This sex bias has severe implications: sexes differ in the way they use external cues to organize their life cycles, but often cue in on each other's physiology and behavior. The simultaneous investigation of both males and females within single studies is thus essential. In this review, I begin by illustrating the sex-bias in studies and attempt to explain its origin. I then provide a number of examples in which focusing on a single sex would have resulted in misleading conclusions. Finally, I review some classical studies of female reproductive physiology that have promoted and developed research on the "forgotten-sex".
Collapse
Affiliation(s)
- Samuel P Caro
- Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 50, 6700 AB Wageningen, The Netherlands.
| |
Collapse
|
16
|
Johnson MA, Cohen RE, Vandecar JR, Wade J. Relationships among reproductive morphology, behavior, and testosterone in a natural population of green anole lizards. Physiol Behav 2011; 104:437-45. [DOI: 10.1016/j.physbeh.2011.05.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Revised: 04/11/2011] [Accepted: 05/03/2011] [Indexed: 10/18/2022]
|
17
|
Hau M, Beebe K. Plastic endocrine regulation of year-round territorial aggression in tropical male spotted antbirds. Gen Comp Endocrinol 2011; 172:305-13. [PMID: 21447333 DOI: 10.1016/j.ygcen.2011.03.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Revised: 03/14/2011] [Accepted: 03/19/2011] [Indexed: 12/16/2022]
Abstract
Studies investigating the hormonal regulation of aggression often focus on the role of the steroid hormone testosterone (T). These studies have generally found an association in temperate zone species between T and male aggression in a reproductive context. However, in most temperate zone species seasonal variation in reproductive context cannot easily be separated from concomitant seasonal changes in other variables, including territory location and partner presence. Therefore, we investigated the hormonal regulation of territorial aggression in a tropical bird that breeds seasonally, but remains mated and territorial year-round. Free-living male spotted antbirds (Hylophylax n. naevioides) displayed similar aggressive behavior in the non-breeding, early, and middle breeding seasons when exposed to a simulated territorial intrusion (STI). Plasma T concentrations after STIs were low and seasonally invariant, but plasma dehydroepiandrosterone (DHEA) was elevated during the non-breeding season. Simultaneous administration of pharmacological inhibitors of androgenic and estrogenic actions during the non-breeding season was less effective in reducing aggressive behavior of captive males compared with a previous study conducted during the breeding season. Hence, in male spotted antbirds endocrine mechanisms appear to vary with reproductive context, both in DHEA concentrations and in the importance of T for regulating aggressive behavior. Furthermore, combining the current data with previous findings suggests that short-term increases in T during aggressive interactions in this tropical species are dependent on the context and the intensity of aggressive stimuli, regardless of season.
Collapse
Affiliation(s)
- Michaela Hau
- Max Planck Institute for Ornithology, Department of Migration and Immuno-Ecology, Radolfzell, Germany.
| | | |
Collapse
|
18
|
Husak JF, Irschick DJ. Steroid use and human performance: Lessons for integrative biologists. Integr Comp Biol 2009; 49:354-64. [PMID: 21665826 DOI: 10.1093/icb/icp015] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
While recent studies have begun to address how hormones mediate whole-animal performance traits, the field conspicuously lags behind research conducted on humans. Recent studies of human steroid use have revealed that steroid use increases muscle cross-sectional area and mass, largely due to increases in protein synthesis, and muscle fiber hypertrophy attributable to an increased number of satellite cells and myonuclei per unit area. These biochemical and cellular effects on skeletal muscle morphology translate into increased power and work during weight-lifting and enhanced performance in burst, sprinting activities. However, there are no unequivocal data that human steroid use enhances endurance performance or muscle fatigability or recovery. The effects of steroids on human morphology and performance are in general consistent with results found for nonhuman animals, though there are notable discrepancies. However, some of the discrepancies may be due to a paucity of comparative data on how testosterone affects muscle physiology and subsequent performance across different regions of the body and across vertebrate taxa. Therefore, we advocate more research on the basic relationships among hormones, morphology, and performance. Based on results from human studies, we recommend that integrative biologists interested in studying hormone regulation of performance should take into account training, timing of administration, and dosage administered when designing experiments or field studies. We also argue that more information is needed on the long-term effects of hormone manipulation on performance and fitness.
Collapse
Affiliation(s)
- Jerry F Husak
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA.
| | | |
Collapse
|
19
|
Garamszegi L, Hirschenhauser K, Bókony V, Eens M, Hurtrez‐Boussès S, Møller A, Oliveira R, Wingfield J. Latitudinal Distribution, Migration, and Testosterone Levels in Birds. Am Nat 2008; 172:533-46. [DOI: 10.1086/590955] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
|
20
|
Fusani L. Endocrinology in field studies: problems and solutions for the experimental design. Gen Comp Endocrinol 2008; 157:249-53. [PMID: 18550056 DOI: 10.1016/j.ygcen.2008.04.016] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 04/18/2008] [Accepted: 04/30/2008] [Indexed: 11/25/2022]
Abstract
The increasing interest in hormones among field biologists can be frustrating because of the difficulties of applying classical endocrinological methods to natural settings. A few thoroughly tested methods have become popular because of their simplicity of use. This does not mean that such methods are the best or the appropriate ones for all studies. In this brief review I will examine some common problems encountered by field biologists who want to study the relationships between a morphological, behavioral, or physiological trait and a hormone. First, I will discuss why questions asked in the field often differ substantially from those asked in the laboratory, and how to adapt the design of the experiment accordingly. Second, I will review alternative methods to study hormone-trait relationships and how to combine them to strengthen the conclusions that can be drawn from the study. Then, I will discuss how to find the right control for a hormonal manipulation. Finally, I will examine the pitfalls associated with long-term hormonal treatment and the available methods for such types of studies.
Collapse
Affiliation(s)
- Leonida Fusani
- Department of Biology and Evolution, University of Ferrara, Via Luigi Borsari 46, 44100 Ferrara, Italy.
| |
Collapse
|
21
|
Canoine V, Fusani L, Schlinger B, Hau M. Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain. Dev Neurobiol 2007; 67:57-67. [PMID: 17443772 DOI: 10.1002/dneu.20296] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Male aggressive behavior is generally regulated by testosterone (T). In most temperate breeding males, aggressive behavior is only expressed during the reproductive period. At this time circulating T concentrations, brain steroid receptors, and steroid metabolic enzymes are elevated in many species relative to the nonreproductive period. Many tropical birds, however, display aggressive behavior both during the breeding and the nonbreeding season, but plasma levels of T can remain low throughout the year and show little seasonal fluctuation. Studies on the year-round territorial spotted antbird (Hylophylax n. naevioides) suggest that T nevertheless regulates aggressive behavior in both the breeding and nonbreeding season. We hypothesize that to regulate aggressive behaviors during the nonbreeding season, when T is at its minimum, male spotted antbirds increase brain sensitivity to steroids. This can be achieved by locally up-regulating androgen receptors (ARs), estrogen receptors (ERs), or the enzyme aromatase (AROM) that converts T into estradiol. We therefore compared mRNA expression of AR, ERalpha, and AROM in free- living male spotted antbirds across reproductive and nonreproductive seasons in two brain regions known to regulate both reproductive and aggressive behaviors. mRNA expression of ERalpha in the preoptic area and AR in the nucleus taeniae were elevated in male spotted antbirds during the nonbreeding season when circulating T concentrations were low. This unusual seasonal receptor regulation may represent a means for the year-round regulation of vertebrate aggressive behavior via steroids by increasing the brain's sensitivity to sex steroids during the nonbreeding season.
Collapse
Affiliation(s)
- Virginie Canoine
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA.
| | | | | | | |
Collapse
|
22
|
Horton BM, Long JA, Holberton RL. Intraperitoneal delivery of exogenous corticosterone via osmotic pump in a passerine bird. Gen Comp Endocrinol 2007; 152:8-13. [PMID: 17428484 DOI: 10.1016/j.ygcen.2007.02.030] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Revised: 02/22/2007] [Accepted: 02/27/2007] [Indexed: 11/21/2022]
Abstract
Selecting the most reliable method to deliver exogenous steroids remains a problem for researchers, particularly when designing experiments on small birds. We used intraperitoneal (IP) osmotic pumps to deliver exogenous corticosterone (CORT) and RU486 in captive White-throated Sparrows. Males received implants containing either a low (LD) or moderate dose (MD) of CORT, RU486 (RU), or polyethylene glycol vehicle only (V). This method provided sustained elevations in baseline CORT in both LD and MD males compared to V males, with higher CORT levels induced in MD males. Slight increases in post-implant CORT resulted in V males, but not in RU males. We observed no significant change in the condition of V males in terms of body mass, furcular fat score or food intake rates, although locomotor activity declined slightly after implantation. Taken together, our results suggest that IP pumps had little impact on the overall health of the birds. CORT levels were maintained within natural ranges for this species, suggesting that our results are biologically relevant and useful for future endocrine studies with small birds.
Collapse
Affiliation(s)
- Brent M Horton
- Department of Biological Sciences, University of Maine, Orono, USA.
| | | | | |
Collapse
|
23
|
Meitzen J, Perkel DJ, Brenowitz EA. Seasonal changes in intrinsic electrophysiological activity of song control neurons in wild song sparrows. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2007; 193:677-83. [PMID: 17440735 DOI: 10.1007/s00359-007-0222-1] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2007] [Revised: 03/19/2007] [Accepted: 03/21/2007] [Indexed: 12/26/2022]
Abstract
Song behavior and its underlying neural substrate can change seasonally in adult songbirds. To test whether environmental cues induce seasonal changes in electrophysiological characteristics of song control neurons, we measured in vitro intrinsic neuronal activity in the song control nucleus RA of adult male song sparrows (Melospiza melodia) in both the fall non-breeding and spring breeding seasons. We found that RA neurons in spring-captured birds show a more than threefold increase in spontaneous firing rate compared to those from fall-captured birds. We conclude that environmental cues are sufficient to induce seasonal changes in electrophysiological properties of song control neurons, and that changes in these properties may underlie seasonal changes in song behavior.
Collapse
Affiliation(s)
- John Meitzen
- Graduate Program in Neurobiology and Behavior, University of Washington, Seattle, WA 98195, USA.
| | | | | |
Collapse
|
24
|
Santangelo N, Bass AH. New insights into neuropeptide modulation of aggression: field studies of arginine vasotocin in a territorial tropical damselfish. Proc Biol Sci 2007; 273:3085-92. [PMID: 17015351 PMCID: PMC1679891 DOI: 10.1098/rspb.2006.3683] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The neuropeptides arginine vasotocin (AVT) and arginine vasopressin are key modulators of affiliation and aggression among non-mammalian and mammalian vertebrates, respectively. Here, we explored AVT's effect on aggression in a wild population of beaugregory damselfish, Stegastes leucostictus, a highly territorial species. Aggression by territorial males towards 'intruders' (bottled fishes) was assessed before and after each male received intramuscular injections of either AVT, Manning compound (an AVT V1a receptor antagonist), isotocin (the teleost homologue of mammalian oxytocin differing from AVT by two amino acids) or saline (vehicle control). Compared to saline controls, AVT and Manning increased and decreased aggression, respectively, while isotocin had no effect. Response selectivity was further established in a dose-response study that revealed an inverted U-shaped function. Compared to saline controls, aggression levels for low and high AVT doses were similar, while medium dose treatments were significantly greater. This type of behavioural response, the first that we know of for a vertebrate neuropeptide, could depend on the binding of AVT to both V1-type and other AVT or non-AVT receptors. The pattern revealed here for damselfish may be symptomatic of species- and context-dependent specificity of AVT's modulation of aggression across teleosts, as is currently proposed for tetrapods.
Collapse
Affiliation(s)
- Nick Santangelo
- Department of Neurobiology and Behaviour, Cornell University, Mudd Hall, Ithaca, NY 14853, USA.
| | | |
Collapse
|
25
|
Canoine V, Fusani L, Schlinger B, Hau M. Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain. ACTA ACUST UNITED AC 2007. [DOI: 10.1002/neu.20296] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
26
|
Use of ethanol for preserving steroid and indoleamine hormones in bird plasma. Gen Comp Endocrinol 2006; 150:191-5. [PMID: 17094990 DOI: 10.1016/j.ygcen.2006.09.014] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/06/2006] [Revised: 09/25/2006] [Accepted: 09/30/2006] [Indexed: 10/23/2022]
Abstract
Endocrinological research on wild animals inhabiting remote areas has been hampered by the need to store plasma samples at subzero temperatures. In an attempt to remedy this logistical issue, we here investigate the use of ethanol as an alternative to freezing for the preservation of steroid and indoleamine hormones in avian plasma. Known quantities of the steroids 5alpha-dihydrotestosterone (DHT), testosterone, 17beta-estradiol, corticosterone, and the indoleamine melatonin were added to a stripped pool of chicken plasma. Samples were either immediately frozen at -40 degrees C, or treated with pure ethanol. Ethanol-treated samples were either immediately frozen, or-to simulate storage conditions at various field locations-left sitting at room temperature for one to two months, or incubated at 36 degrees C for one month before all treatment groups were frozen at -40 degrees C. All samples were then analyzed by radioimmunoassay. For DHT and estradiol there were no differences among treatment groups suggesting that ethanol-treatment is as effective as immediate freezing in preserving plasma steroid concentrations. For testosterone, corticosterone and melatonin ethanol-treated samples differed significantly from immediately frozen samples suggesting that caution is needed when comparing absolute concentrations of hormones between samples preserved in different ways. However, differences among ethanol-treated samples in general were small, demonstrating the feasibility of this preservation method in the field at remote locations.
Collapse
|
27
|
Schuett GW, Repp RA, Taylor EN, DeNardo DF, Earley RL, Van Kirk EA, Murdoch WJ. Winter profile of plasma sex steroid levels in free-living male western diamond-backed rattlesnakes, Crotalus atrox (Serpentes: Viperidae). Gen Comp Endocrinol 2006; 149:72-80. [PMID: 16828091 DOI: 10.1016/j.ygcen.2006.05.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2005] [Revised: 05/08/2006] [Accepted: 05/10/2006] [Indexed: 11/20/2022]
Abstract
Recent field studies on the reproductive ecology of western diamond-backed rattlesnakes (Crotalus atrox) from populations in southern Arizona showed significant differences in the concentration of plasma sex steroids (testosterone, T; 5alpha-dihydrotestosterone, DHT; and 17beta-estradiol, E2) throughout the active season (March-October), and peak levels were coincident with the two mating periods (late summer and early spring). There is, however, no information on levels of sex steroids during winter. Similar to most snakes, hibernating individuals of C. atrox are typically inaccessible, but in southern Arizona, where environmental conditions are typically mild during winter, adult males frequently bask at or near the entrances of communal dens. Basking activity, therefore, offers a unique logistical opportunity to assess the complete annual profile of plasma sex steroid levels in males of a temperate reptile in nature. From November to February, we measured levels of plasma T, DHT, and E2 in adult male C. atrox that were located basking at communal dens. Additionally, cloacal, core body, and ambient air temperatures were obtained to investigate potential relationships between body temperatures and levels of sex steroids. Mean levels of T, DHT, and E2 were relatively high, and the concentration hierarchy was T>DHT>E2. Mean levels of T, DHT, and E2 showed no significant variation across the four months of sampling; however, E2 levels decreased progressively. In the annul cycle, sex steroid levels during winter were not basal when compared to values obtained during the active season. Mean cloacal temperatures of basking males were significantly higher than core body temperatures of non-basking males (inside dens) from November-December, and in February, which suggests that one function of winter basking is to elevate body temperatures. Steroid levels, nonetheless, were not significantly correlated with cloacal temperatures. We suggest that future field studies of male C. atrox should: (a) investigate sex steroid levels in non-basking individuals and (b) test whether elevated levels of sex steroids during winter facilitate the large increases that occur in early spring, which are coincident with the second mating season. Our findings on the reproductive biology of C. atrox and other viperids are discussed in the context of the associated-dissociated model of reproduction.
Collapse
Affiliation(s)
- Gordon W Schuett
- Department of Biology, Center for Behavioral Neuroscience, Georgia State University, 33 Gilmer Street, S. E., Atlanta, GA 30303-3088, USA.
| | | | | | | | | | | | | |
Collapse
|