Primary dermal fibroblasts and pectoralis muscle show similar patterns of oxidative stress in tropical and temperate birds despite differing life‐histories

Abstract

Tropical birds have a 'slower pace of life', with lower rates of whole-animal metabolism, smaller metabolically active organs and lower cellular metabolic rates than their temperate counterparts. Oxidative stress is a physiological mechanism that may dictate differing life-histories such as those found between tropical and temperate birds. Oxygen is required to make ATP, resulting in the production of reactive oxygen species (ROS). If left unchecked, ROS can structurally alter proteins, induce mutations in DNA and damage structural lipids. To combat accumulating oxidative damage, organisms have evolved an elaborate and costly antioxidant system that serves to sequester ROS before they wreak cellular havoc. We examined whether oxidative stress would differ between tropical and temperate birds. We used isolated primary dermal fibroblasts and pectoralis muscle tissue for measurements. We measured four aspects of oxidative stress in primary fibroblasts -reduced glutathione (GSH) concentration, ROS production, mitochondrial content and lipid peroxidation (LPO) damage. We found no significant differences in the four variables between temperate and tropical birds. In muscle tissue, we measured catalase (CAT), superoxide dismutase (SOD) glutathione peroxidase (GPx) activity, peroxyl and hydroxyl scavenging capacity and LPO damage. We found that peroxyl scavenging capacity was significantly higher in tropical birds compared with temperate birds.

Metabolic rate is negatively linked to adult survival but does not explain latitudinal differences in songbirds

“…If tropical species invest in processes that mitigate oxidative stress (e.g. Beattie et al ) by lesser investment in growth or reproduction, such a trade‐off could explain the longer life and slower life‐history strategies of tropical species despite broadly similar metabolic rates across latitudes. However, this trade‐off is only profitable when extrinsic mortality is low.…”

“…These patterns have been interpreted as evidence that metabolic rate and adult survival are causally linked across latitudes. Other studies, in contrast, found no difference in metabolic rates across latitudes in either adult birds (Vleck & Vleck ; Bennett & Harvey ) or embryos (Martin et al ) and levels of oxidative stress were similar across phylogenetically paired tropical and temperate species (Beattie et al ). Latitudinal variation in metabolism may be directly related to extrinsic environmental conditions (White et al ; Jetz et al ) independent of a causal association with survival.…”

“…Yet, metabolism may be decoupled from senescence because mechanisms to prevent or repair damage (e.g. endogenous antioxidants, mitochondrial membrane composition and telomere dynamics) may coevolve with metabolic rate (Brand 2000;Brand et al 2004;Monaghan & Haussmann 2006;Hulbert et al 2007;Costantini 2008;Salin et al 2015;Skrip & Mcwilliams 2016;Vagasi et al 2019;Beattie et al 2019). Furthermore, survival rates may be entirely unrelated to the accumulation of cellular damage entirely (Reznick et al 2004).…”