Do wild-caught urban house sparrows show desensitized stress responses to a novel stressor?

Noraine Salleh Hudin,Diederik Strubbe,Aimeric Teyssier,Joël White,Graham D Fairhurst,Luc Lens,Johan Aerts,Liesbeth De Neve

doi:10.1242/bio.031849

Abstract

ABSTRACTWhile urbanization exposes individuals to novel challenges, urban areas may also constitute stable environments in which seasonal fluctuations are buffered. Baseline and stress-induced plasma corticosterone (cort) levels are often found to be similar in urban and rural populations. Here we aimed to disentangle two possible mechanisms underlying such pattern: (i) urban environments are no more stressful or urban birds have a better ability to habituate to stressors; or (ii) urban birds developed desensitized stress responses. We exposed wild-caught urban and rural house sparrows (Passer domesticus) to combined captivity and diet treatments (urban versus rural diet) and measured corticosterone levels both in natural tail feathers and in regrown homologous ones (cortf). Urban and rural house sparrows showed similar cortf levels in the wild and in response to novel stressors caused by the experiment, supporting the growing notion that urban environments are no more stressful during the non-breeding season than are rural ones. Still, juveniles and males originating from urban populations showed the highest cortf levels in regrown feathers. We did not find evidence that cortf was consistent within individuals across moults. Our study stresses the need for incorporating both intrinsic and environmental factors for the interpretation of variation in cortf between populations.

Highlights

Cortf of regrown feathers was not correlated with fluctuating asymmetry (FA) or growth bar widths (GBW), and there were no interactions with sex, age, urbanization or diet (FA model, all P>0.31; GBW model, all P>0.13)
No descriptive or experimental studies to date have provided conclusive evidence that urban-dwelling passerines such as house sparrows exhibit different HPA axis functioning compared to their rural counterparts (Bókony et al, 2012; Chavéz-Zichinelli et al, 2010; Fokidis et al, 2009; Meillere et al, 2015), while evidence is growing that HPA axis functioning is plastic and variable among ages and sexes (Aharon-Rotman et al, 2017; Dantzer et al, 2014)
Cities may provide urban-dwelling species with favorable foraging opportunities, at least for adults, which appears to contradict the common finding that urban sparrows are often leaner than rural ones (Bókony et al, 2012; Meillere et al, 2015; Salleh Hudin et al, 2016)

Summary

Introduction

Repeated challenges may cause alterations in HPA activity and attenuate the release of cort in response to stressors without the perception that a challenge is no longer threatening [desensitization sensu (Cyr and Romero, 2009; Rich and Romero, 2005)]. In such cases, environmental stressors can affect the organism-wide stress physiology which may incur costs if it comprises an individual’s ability to respond to ecologically-relevant stressors (Cyr and Romero, 2009). If stress continues to increase, the physiological system may eventually break down and cort release may decrease as the stress response can no longer be maintained (Cyr and Romero, 2009)

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