The Relationship between Hormones, Glucose, and Oxidative Damage Is Condition and Stress Dependent in a Free-Living Passerine Bird

Abstract

Physiological state is an emergent property of the interactions among physiological systems within an intricate network. Understanding the connections within this network is one of the goals in physiological ecology. Here, we studied the relationship between body condition, two neuroendocrine hormones (corticosterone and insulin-like growth factor 1 [IGF-1]) as physiological regulators, and two physiological systems related to resource metabolism (glucose) and oxidative balance (malondialdehyde). We measured these traits under baseline and stress-induced conditions in free-living house sparrows (Passer domesticus). We used path analysis to analyze different scenarios about the structure of the physiological network. Our data were most consistent with a model in which corticosterone was the major regulator under baseline conditions. This model shows that individuals in better condition have lower corticosterone levels; corticosterone and IGF-1 levels are positively associated; and oxidative damage is higher when levels of corticosterone, IGF-1, and glucose are elevated. After exposure to acute stress, these relationships were considerably reorganized. In response to acute stress, birds increased their corticosterone and glucose levels and decreased their IGF-1 levels. However, individuals in better condition increased their cor-ticosterone levels more and better maintained their IGF-1 levels in response to acute stress. The acute stress-induced changes in corticosterone and IGF-1 levels were associated with an increase in glucose levels, which in turn was associated with a decrease in oxidative damage. We urge ecophysiologists to focus more on physiological networks, as the relationships between physiological traits are complex and dynamic during the organismal stress response.

Food Restriction Reveals Individual Differences in Insulin-Like Growth Factor-1 Reaction Norms

“…Our finding that heavier birds were more likely to decrease IGF-1 levels under foodrestriction, whereas light birds were more likely to increase it may support the existence of such a physiological turning point, which may explain the variance of IGF-1 reaction norm during food-restriction. Accordingly, the relationships between IGF-1 and other physiological traits such as glucose levels, glucocorticoids and a marker of oxidative stress can be reorganized during environmental challenges (Vágási et al, 2020). These results suggest that the relationship between IGF-1 and other physiological factors is context-and conditiondependent and their joint effect on life-history or fitness-related traits is still unexplored in natural populations.…”

Food restriction delays breeding and affects insulin‐like growth factor‐1, oxidative damage and haematocrit value before egg‐laying in female canaries

“…It is noteworthy that a similar decline in ROM level was not found in the treated group, where plasma IGF‐1 level increased. High levels of IGF‐1 were shown to be related to increased levels of oxidative damage (Holzenberger et al 2003, Vágási et al 2020), therefore it is possible that the increased IGF‐1 level in the treated group prevented the adaptive preparation for an improved oxidative balance before breeding. However, here we could not demonstrate a correlation of plasma IGF‐1 concentration with plasma OXY or ROM levels, thus, other physiological traits may have played important roles in these associations.…”

Does IGF-1 Shape Life-History Trade-Offs? Opposite Associations of IGF-1 With Telomere Length and Body Size in a Free-Living Bird

“…Interestingly, reduced IGF-1 signaling has also been associated with increased in vivo resistance to oxidative stress in laboratory models (Holzenberger et al, 2003). Furthermore, administration of IGF-1 in wild birds was found to lead to greater oxidative damage (Lendvai et al, 2020;Vágási et al, 2020) and higher activity of glutathione peroxidase Lendvai et al, 2020), the later possibly reflecting up-regulated antioxidant activity in response to oxidative stress Lendvai et al, 2020). Variation in oxidative stress and telomere length have been linked to the aging process, with individuals with enhanced resistance to oxidative stress and/or longer telomeres having higher annual survival or better fitness (Bize et al, 2009), and importantly exposure to oxidative stress is thought to accelerate telomere shortening (Reichert and Stier, 2017;but see Pérez-Rodríguez et al, 2019).…”