No simple measures for antioxidant status in birds: complexity in inter- and intraspecific correlations among circulating antioxidant types


  • Alan A. Cohen,

    Corresponding author
    1. Department of Biology, R223 Research Building, University of Missouri-St Louis, 8001 Natural Bridge Road, St Louis, MO 63121, USA
      *Correspondence author. Centre for Global Health Research, 70 Richmond Street, East Suite 202A, Toronto, ON, Canada M5K 1N8. E-mail:
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  • Kevin J. McGraw

    1. School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
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*Correspondence author. Centre for Global Health Research, 70 Richmond Street, East Suite 202A, Toronto, ON, Canada M5K 1N8. E-mail:


  • 1Recently, ecologists have shown interest in examining antioxidant protection in wild animals; carotenoids in particular have received attention as antioxidants that play an important role in mediating health, life-history trade-offs and sexual selection. However, we know almost nothing about the relationships among levels of different antioxidants in wild animals or whether variation in antioxidants can be viewed as a single coherent system.
  • 2Here we use a data set of 903 individuals from 99 bird species to examine covariation among concentrations of three types of antioxidants (uric acid, vitamin E and four carotenoids), and their relationship to a summary measure, Trolox-equivalent antioxidant capacity (TEAC), both inter- and intraspecifically in 30 species.
  • 3Three axes were necessary to adequately describe variation in nine antioxidant measures, and these axes corresponded to the basic categories of antioxidant measured: uric acid, vitamin E and carotenoids. There was substantial heterogeneity in the correlations across species.
  • 4TEAC covaried strongly with uric acid levels, both interspecifically and in 23 of the 30 species. Concentrations of different carotenoids covaried both inter- and intraspecifically, but there was also substantial variance explained by each carotenoid independent of the others. Vitamin E concentration did not robustly correlate with any other antioxidant parameters.
  • 5Overall, we show that although antioxidants tend to covary with those of similar type, these correlations demonstrate evolutionary lability and/or ecological heterogeneity. Even the most general associations are absent in some species, suggesting that conceptualization of a single antioxidant system is oversimplified and that ecological studies attempting to examine antioxidant function should use multiple measures.