Individual Condition and Mitochodnrial Function

Condition is a nearly ubiquitous term in the behavioral, physiological, and evolutionary literature on ornamental traits in animals, yet existing definitions are incomplete or ambiguous.  Too often in the literature, condition is defined as nutrient reserves with signal honesty being maintained by tradeoffs in the distribution of the pools of resources that define condition.  This poor conceptualization has led to confusion regarding what is being signaled by condition-dependent traits and how to interpret links between ornamentation and individual characteristics such as nutrient reserves, oxidative state, and immunocompetence.   In an Ideas paper in Ecology Letter, I recently proposed that the combined effects of the somatic state, epigenetic state, and genotype of an organism determine condition.  I defined condition as the relative capacity to maintain optimal functionality of vital systems within the body.   My lab group is particularly interested in testing the idea that links between certain ornamental traits like carotenoid coloration or cognitive displays and performance such as immunocompetence arise because both ornaments and performance require high mitochondrial function.  We are testing this idea both with experiments with birds and copepods and by writing synthesis papers that bring insights from cell biology to behavioral ecology.

Key recent citations related to condition from the Hill Lab:

Weaver, R. J., R. E. Koch, and G. E. Hill. 2017. What maintains signal honesty in animal color displays used in mate choice? Phil. Trans. Roy. Soc. Lond. 372(1724) 


RE Koch, AN Kavazis, D Hasselquist, WR Hood, Y Zhang, MB Toomey, G E Hill. 2018. No evidence that carotenoid pigments boost either immune or antioxidant defenses in a songbird. Nature communications 9 (1), 491

RE Koch, GE Hill. 2018. Behavioural mating displays depend on mitochondrial function: a potential mechanism for linking behaviour to individual condition.  Biological Reviews

RE Koch, GE Hill. 2018. Do carotenoid‐based ornaments entail resource trade-offs? An evaluation of theory and data.  Functional Ecology

Koch, R.E., C.J. Josefson, and G.E. Hill. 2016. Mitochondrial function, ornamentation, and immunocompetence. Biological Reviews.

Weaver, R. J., Hill G E., Kuan P L, and Tseng,Y-C. 2016. Copper exposure reduces production of red carotenoids in a marine copepod. Environmental Indicators 70:393-400.

232. Koch, R. E. and G. E. Hill. 2016. An assessment of techniques to manipulate oxidative stress in animals. Functional Ecology doi:10.1111/1365-2435.12664

Ge, R., Johnson, J.D., P. A. Cobine, K. J. McGraw, R. Garcia, G. E. Hill. 2015. High concentrations of keto-carotenoids found in the Hepatic Mitochondrial fraction of a molting red songbird. Physiological and Biochemical Zoology 88.4: 444-450.

Balenger S. L. Bonneaud, C., Sefick, S., Edwards, S. V., Hill, G. E. 2015. Plumage color and pathogen-induced gene expression in a wild songbird. Behavioral Ecology 26(4), 1100–1110. doi:10.1093/beheco/arv055


Hill, G. E. 2014. Stress, condition, and ornamentation. Integrative and Comparative Biology 54: 533-538.


Hill, G. E. 2014. Cellular respiration: the nexus of stress, condition, and ornamentation. Integrative and Comparative Biology 54: 539-554.


McGraw, K. J., Giraudeau, M., Hill, G. E., Toomey, M. B., & Staley, M. (2013). Ketocarotenoid circulation, but not retinal carotenoid accumulation, is linked to eye disease status in a wild songbird. Archives of Biochemistry and Biophysics. 539(2): 156-162.

Hill, G. E. and J. D. Johnson. 2013. The Vitamin A-Redox Hypothesis: A Biochemical Basis for Honest Signaling via Carotenoid Pigmentation. American Naturalist.

Hill, G. E. 2011. Condition-dependent traits as signals of the functionality of vital cellular processes. Ecology Letters 14: 625-634.

The Hill Lab

Dept of Biological Sciences, Auburn University

331 Funchess Hall
Auburn, AL 36849-5414


Phone: (334) 844-9269

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