Elsevier

Hormones and Behavior

Volume 128, February 2021, 104913
Hormones and Behavior

Acute aggressive behavior perturbates the oxidative status of a wild bird independently of testosterone and progesterone

https://doi.org/10.1016/j.yhbeh.2020.104913Get rights and content

Highlights

  • Acute aggressive interactions perturbate the oxidative status of a wild vertebrate.

  • Acute aggressive interactions generate a decrease in antioxidant capacity.

  • Changes in oxidative status are independent of testosterone and progesterone.

  • Changes in oxidative status are stronger in females than males.

Abstract

Aerobically demanding activities like aggression can lead to an elevated oxidative metabolism affecting the concentration of pro-oxidant and antioxidant compounds and can result in an overall perturbation of the oxidative status. Aggression may also alter the oxidative status indirectly through an increase in testosterone and progesterone concentrations. Given that changes in the oxidative status could represent a physiological cost of aggression, we tested the hypothesis that acute conspecific aggression impairs the oxidative status and evaluated the role of testosterone and progesterone as potential mediators. To achieve this, we experimentally manipulated the aggressive behavior of wild female and male birds and measured the concentrations of pro-oxidants, enzymatic- and non-enzymatic antioxidants, testosterone and progesterone in blood. After 20 min of conspecific aggressive behavior, both sexes had lower concentrations of non-enzymatic antioxidants than control individuals. This effect was independent of testosterone and progesterone concentrations, and much stronger in females than in males. Further, only in females (but not in males) being more aggressive came at the expense of lower antioxidant concentration. We provide the first experimental evidence that acute aggressive behavior perturbates the oxidative state of a wild vertebrate independently of testosterone and progesterone, with potential ecological and evolutionary implications given the role of the redox system in shaping life-history traits.

Introduction

Animals frequently engage in aggressive behaviors to obtain and secure limited resources that can enhance their reproductive success, such as a breeding territory (Beckman and Ames, 1998; Duckworth, 2006; Demas et al., 2007; Rosvall, 2008; Smith and Blumstein, 2008; Clutton-Brock, 2009). However, aggressive behaviors entail costs (e.g., territory loss or injuries), which could partially explain why individuals differ in their degree of aggressiveness. A particularly relevant but understudied cost associated with this behavior concerns the oxidative state of an individual (Costantini et al., 2008; Isaksson et al., 2011). The oxidative state of an individual is determined by the concentration of pro-oxidants (i.e., reactive oxygen species) and antioxidants (i.e., non-enzymatic and enzymatic compounds) present in cells and tissues (reviewed by Costantini, 2019). A change in any of these molecular components in favor of pro-oxidants can lead to damage of biomolecules such as lipids, proteins and DNA (reviewed by Costantini, 2008; Monaghan et al., 2009). This damage can shape life-history decisions of individuals as well as life history traits such as reproduction and longevity (e.g., Finkel and Holbrook, 2000; Costantini, 2008; Monaghan et al., 2009), potentially translating into ecological and evolutionary consequences.

Aggressive behaviors are energetically demanding activities that increase the metabolic rate, exposing an individual to an elevated concentration of pro-oxidants (Fig. 1a; Costantini, 2008; Powers and Jackson, 2008; Skrip and McWilliams, 2016; Cooper-Mullin and McWilliams, 2016; but see Salin et al., 2015). Such perturbations in the oxidative status of animals are expected since more than 90% of the cellular energy is generated by the mitochondria (Bottje, 2015) and natural by-products of aerobic respiration are reactive oxygen species (ROS). However, our understanding of aggression altering the oxidative state is still in its early stages. In selected lines of mice (Mus musculus domesticus), aggressive males had lower levels of antioxidants than non-aggressive males (Costantini et al., 2008). In contrast, aggressive males of wild-caught white skinks (Egernia whitii) had higher levels of non-enzymatic antioxidants than less aggressive males, whereas in females no such relationship was apparent (Isaksson et al., 2011). Acute aggressive behaviors, such as territorial fights, that represent an increase in energy expenditure, could also incur an oxidative challenge; yet it remains unknown whether this is the case.

The oxidative state of an individual can be indirectly altered by aggressive behaviors through an increase in steroid hormone concentrations (Fig. 1b; Schantz et al., 1999; Alonso-Alvarez et al., 2007). The sex steroid testosterone is assumed to be the key hormone related to resource-defense aggression and can increase during aggressive interactions in males (Wingfield et al., 1990; Hirschenhauser and Oliveira, 2006; Goymann et al., 2007; Hau, 2007). Testosterone has been proposed to be a cause of increased ROS production (e.g., Alonso-Alvarez et al., 2007; Koch et al., 2016), which can occur either because testosterone enhances the metabolic rate of individuals (e.g., Marler and Moore, 1989; Welle et al., 1992; Wikelski et al., 1999; Buchanan et al., 2001; Koch et al., 2016) and/or because testosterone has intrinsic oxidative properties (e.g., Zhu et al., 1997; Chainy et al., 2009; Casagrande et al., 2011). An increase in aggressive behavior after a territorial intrusion can, therefore, potentially lead to an increase in testosterone concentrations (e.g., Wingfield and Wada, 1989; Wingfield and Hahn, 1994; McGlothlin et al., 2008), with testosterone levels influencing the concentrations of pro-oxidant and antioxidant compounds and resulting in an overall perturbation of the oxidative state. To date, only one study has looked at the relationship between aggression, oxidative status and testosterone concentrations in a wild-caught vertebrate (Isaksson et al., 2011). Isaksson et al. (2011) found that the aggressive phenotype of male white skinks, but not testosterone concentrations, was positively related to the oxidative condition of individuals. Aggression can also be associated with another steroid hormone: progesterone. Progesterone has been mainly proposed as a mediator of aggressive behavior in females (e.g., Goymann et al., 2008; but see e.g., Adreani et al., 2018). As with testosterone, progesterone can increase the metabolic rate of organisms (Gavrilova-Jordan and Price, 2007) and the concentration of pro-oxidants (only from studies done in vitro e.g., Zhu et al., 1997; Itagaki et al., 2005). Investigating the relationships between aggressive behavior, oxidative status, testosterone and progesterone in females and males is fundamental if we aim to understand the sex-specificity of these physiological pathways.

The main goal of our study was to test the hypothesis that an acute increase in conspecific aggressive behavior can impair the oxidative status of wild rufous horneros (Aves: Furnarius rufus, hereafter termed hornero), and to test whether this was related to testosterone and progesterone concentrations. To elicit an aggressive response, we challenged female and male birds with 20 min of simulated conspecific territorial intrusions (STI) during the nest-building period. Immediately after the STI we collected blood samples to measure the concentrations of three oxidative status markers, testosterone and progesterone. We then compared these concentrations with the ones of birds that did not engage in aggressive behaviors. The hornero represents an excellent model system to study the effects of acute aggression across sexes. It is a seasonal breeder, and both females and males are involved in territorial defense throughout the year (Fraga, 1980; Diniz et al., 2016; Mentesana et al. 2020). Further, horneros are sexually monomorphic in plumage coloration and body size (i.e., there is no difference in body condition between sexes; Diniz et al., 2016), and all breeding behaviors studied so far, except for aggressive behaviors, are shared and coordinated between the sexes (Massoni et al., 2012; Diniz et al., 2018; Mentesana et al. 2020).

Section snippets

Field site and simulated territorial intrusion (STI)

The study was conducted between August 22nd and September 28th of 2016 on the campus of INIA ‘Las Brujas’ (National Institute of Agricultural Research), Department of Canelones, Uruguay (34°40′ S, 56°20′ W; 0–35 m a.s.l.). During this period, horneros were building their nests and females were close to egg laying. In total, we collected behavioral and physiological data from birds defending 51 territories that were subjected to the experimental treatments between 7 am and 1 pm.

We experimentally

Sex differences in the concentrations of oxidative markers, testosterone and progesterone of control birds

Control females had a lower non-enzymatic antioxidant capacity (OXY) than control males (Fig. 2A; p(dif.) > 99.99%, Table S3). Both sexes had similar enzymatic antioxidant concentrations (GPX; Fig. 2B; p(dif.) = 79.03%, Table S3). We found a trend for control males having lower levels of pro-oxidants than females (ROMs; Fig. 2C; p(dif.) = 94.67%, Table S3). Control females had lower testosterone concentrations than control males (Fig. 2D; p(dif.) = 99.86%, Table S3), but we found no difference

Discussion

We experimentally tested if conspecific aggressive behavior induced an acute change in the oxidative state of female and male wild birds, and whether this effect was mediated by testosterone or progesterone. Our results provide the first evidence that an acute increase in conspecific aggressive behavior (i.e., for 20 min) perturbates the oxidative status of an individual by decreasing the concentration of non-enzymatic antioxidants in plasma. This perturbation in oxidative condition was not

Conclusions

Our study provides the first evidence that an acute increase in aggressive behavior perturbates the oxidative state of female and male wild birds. Our study also suggests that the mechanisms underlying these changes differ between sexes. Until now, the effect of aggression on the oxidative state was investigated in the framework of personality traits (Costantini et al., 2008; Isaksson et al., 2011). Altogether, the existing studies suggest that aggressive behaviors performed over both short and

Author Contributions

NMA and LM contributed equally in the study. Both conceived and designed the study, secured funding and analysed the data. LM took lead in writing the initial version of the mauscript and NMA provided critical feedback and helped shape the manuscript.

Ethical statement

The experimental procedures were approved by the Ethics Committee of Animal Experimentation (CEUA) of the Facultad de Ciencias, Universidad de la República, Uruguay (University of the Republic of Uruguay). Protocol number 186, file 2400-11000090-16.

Funding

We acknowledge funding and support from the International Max Planck Research School (IMPRS) for Organismal Biology (Max Planck Institute, Germany), and by Idea Wild (USA) that provided field equipment.

Declaration of competing interest

We declare no competing interests.

Acknowledgements

We thank Enzo Cavalli and Ernesto Guedes for their assistance in the field, and Monika Trappschuh for conducting the hormone analysis. We also thank the members from the Ethology Lab at the Universidad de la República in Montevideo and especially to Bettina Tassino for their support. Also, we thank all the “INIA Las Brujas” staff for providing us with accommodation and equipment during fieldwork. Furthermore, we are thankful to Juan Carlos Reboreda and the Ecology and Behaviour lab (LEyCA) from

References (78)

  • C.P. Villavicencio et al.

    The number of life-history stages does not influence the androgen responsiveness to male–male interactions: sedentary and migratory black redstarts (Phoenicurus ochruros) do not elevate testosterone in response to simulated territorial intrusions

    Gen. Comp. Endocrinol.

    (2014)
  • J.C. Wingfield et al.

    Testosterone and territorial behaviour in sedentary and migratory sparrows

    Anim. Behav.

    (1994)
  • X.D. Zhu et al.

    17β-Estradiol, progesterone, and testosterone inversely modulate low- density lipoprotein oxidation and cytotoxicity in cultured placental trophoblast and macrophages

    Am. J. Obstet. Gynecol.

    (1997)
  • C. Alonso-Alvarez et al.

    Testosterone and oxidative stress: the oxidation handicap hypothesis

    Proc. R. Soc. Lond. B Biol. Sci

    (2007)
  • B. Apfelbeck et al.

    Ignoring the challenge? Male black redstarts (Phoenicurus ochruros) do not increase testosterone levels during territorial conflicts but they do so in response to gonadotropin-releasing hormone

    Proceedings. Biological Sciences

    (2011)
  • Y.G. Araya-Ajoy et al.

    Characterizing behavioural “characters”: an evolutionary framework

    Proc. R. Soc. Lond. B Biol. Sci.

    (2013)
  • K.B. Beckman et al.

    The free radical theory of aging matures

    Physiol. Rev.

    (1998)
  • K.L. Buchanan et al.

    Testosterone influences basal metabolic rate in male house sparrows: a new cost of dominance signalling?

    Proc. R. Soc. Lond. Ser. B Biol. Sci.

    (2001)
  • S. Casagrande et al.

    Enzymatic antioxidants but not baseline glucocorticoids mediate the reproduction–survival trade-off in a wild bird

    Proc. R. Soc. Lond. B Biol. Sci.

    (2018)
  • S. Casagrande et al.

    Differential effects of testosterone, dihydrotestosterone and estradiol on carotenoid deposition in an avian sexually selected signal

    J. Comp. Physiol

    (2011)
  • G.B.N. Chainy et al.

    Testosterone-induced changes in testicular antioxidant system

    Andrologia

    (2009)
  • C. Cooper-Mullin et al.

    The role of the antioxidant system during intense endurance exercise: lessons from migrating birds

    J. Exp. Biol.

    (2016)
  • D. Costantini

    Oxidative stress in ecology and evolution: lessons from avian studies

    Ecol. Lett.

    (2008)
  • D. Costantini

    Understanding diversity in oxidative status and oxidative stress: the opportunities and challenges ahead

    J. Exp. Biol.

    (2019)
  • D. Costantini et al.

    Correlates of oxidative stress in wild kestrel nestlings (Falco tinnunculus)

    J. Comp. Physiol. B.

    (2006)
  • Costantini, D., Carere, C., Caramaschi, D., & Koolhaas, J. M. (2008). Aggressive and non-aggressive personalities...
  • D. Costantini et al.

    Biochemical integration of blood redox state in captive zebra finches (Taeniopygia guttata)

    J. Exp. Biol.

    (2011)
  • D. Costantini et al.

    A meta-analysis of glucocorticoids as modulators of oxidative stress in vertebrates

    J. Comp. Physiol. B.

    (2011)
  • Demas, G. E., Cooper, M. A., Albers, H.E., & Soma, K.K. (2007). Novel mechanisms underlying neuroendocrine regulation...
  • P. Diniz et al.

    Monochromatism, cryptic sexual dimorphism and lack of assortative mating in the Rufous Hornero, Furnarius rufus albogularis

    Emu - Austral Ornithology

    (2016)
  • P. Diniz et al.

    Duetting behavior in a Neotropical ovenbird: sexual and seasonal variation and adaptive signaling functions

    J. Avian Biol.

    (2018)
  • R.A. Duckworth

    Aggressive behaviour affects selection on morphology by influencing settlement patterns in a passerine bird

    Proc. R. Soc. Lond. B Biol. Sci.

    (2006)
  • T. Finkel et al.

    Oxidants, oxidative stress and the biology of ageing

    Nature

    (2000)
  • R.M. Fraga

    The breeding of Rufous Horneros (Furnarius rufus)

    Condor

    (1980)
  • B.G. Freeman et al.

    Evolution and plasticity: divergence of song discrimination is faster in birds with innate song than in song learners in Neotropical passerine birds

    Evolution

    (2017)
  • L. Gavrilova-Jordan et al.

    Actions of steroids in mitochondria

    Semin. Reprod. Med.

    (2007)
  • A. Gelman et al.

    Data Analysis Using Regression and Multilevel/Hierarchical Models

    (2007)
  • S.A. Gill et al.

    Context matters: female aggression and testosterone in a year-round territorial neotropical songbird (Thryothorus leucotis)

    Proc. R. Soc. B Biol. Sci.

    (2007)
  • W. Goymann et al.

    Progesterone modulates aggression in sex-role reversed female African black coucals

    Proc. R. Soc. Lond. B Biol. Sci.

    (2008)
  • Cited by (0)

    View full text