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Abstract Many organisms engage in metabolic tradeoffs to manage costs associated with reproductive output which often leads to these costs carrying over into the future. Compensatory mechanisms vary across life history strategies and are expected to result in near-optimal fitness gains for the investor. Here we investigated whether environmental differences associated with increasing montane elevation and variation in reproductive output of a resident passerine songbird, the Mountain Chickadee (Poecile gambeli), were related to physiological conditions during annual molt. Higher elevations are associated with harsher environmental conditions during the winter, which results in later and shorter breeding seasons than at lower elevations. We sampled the outermost tail feathers from adult birds in the fall after their prebasic molt, which initiates closely after reproduction (e.g., after parental care has ceased, ~1–3 weeks). We measured the hormone corticosterone deposited in feathers (fCORT) and feather growth rates for evidence of physiological effort predicted to be driven by several units of reproductive output (e.g., breeding timing, clutch and brood size, and offspring mass). There were no relationships between any measure of reproductive output and feather characteristics between elevations or across years, despite substantial variation in reproductive output in the wider population across this same time. However, birds at the high-elevation site grew their tail feathers significantly faster and had higher fCORT deposition compared to low-elevation birds. These results suggest that although differences in reproductive output and any related signals of associated physiological effort (e.g., fCORT and feather growth rate) may not extend into individual conditions during annual molt, shorter breeding seasons associated with harsher environmental conditions may favor faster feather growth as required by earlier onset of winter.
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Long term stability of corticosterone in feathers
Measuring corticosterone in feathers allows researchers to make long-term, retrospective assessments of physiology with non-invasive sampling. To date, there is little evidence that steroids degrade within the feather matrix, however this has yet to be determined from the same sample over many years. In 2009, we made a pool of European starling (Sturnus vulgaris) feathers that had been ground to a homogenous powder using a ball mill and stored on a laboratory bench. Over the past 14 years, a subset of this pooled sample has been assayed via radioimmunoassay (RIA) 19 times to quantify corticosterone. Despite high variability across time (though low variability within assays), there was no effect of time on measured feather corticosterone concentration. In contrast, two enzyme immunoassays (EIA) produced higher concentrations than the samples assayed with RIA, though this difference is likely due to different binding affinities of the antibodies used. The present study provides further support for researchers to use specimens stored long-term and from museums for feather corticosterone quantification, and likely applies to corticosteroid measurements in other keratinized tissues.
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- Award ID(s):
- 1655269
- PAR ID:
- 10469498
- Publisher / Repository:
- Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology
- Date Published:
- Journal Name:
- Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology
- Volume:
- 283
- Issue:
- C
- ISSN:
- 1095-6433
- Page Range / eLocation ID:
- 111472
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.cbpa.2023.111472
