Avian fitness: birds go easy on their pectoral muscles

Common quails, Photo: Gianni Pola

Common quails, Photo: Gianni Pola  1

A European research team led by Vetmeduni Vienna has discovered a protective mechanism in migratory birds. According to the study, common quails are able to specifically safeguard their pectoral muscles from oxidative stress during migration. The researchers believe this mechanism is an essential factor in the ability of migratory birds to successfully complete their long flights.

High caloric intake, as seen in migratory birds during their travels, can increase the production of reactive oxygen and nitrogen compounds. These free radicals can damage vitally important molecules, including nucleic acids, proteins and lipids, resulting in oxidative stress. However, aerobic organisms have various defensive strategies using both exogenous and endogenously produced antioxidants to counteract such damage. Studies of different vertebrate species show that changes in oxidative status can have fitness consequences, for example influencing the probability of survival and reproductive behaviour.

Bird migration accompanied by tissue-specific changes in oxidative status

A team of researchers led by Valeria Marasco from the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine Vienna studied a captive population of common quails (Coturnix coturnix) to examine whether the emergence of the migratory phenotype, which is primarily signalled by increased food intake and fuelling, is accompanied by changes in oxidative status. The researchers induced autumn migration in the birds, followed by a non-migratory wintering phase, and then compared three markers of oxidative status: thiobarbituric acid reactive substances (TBARS); superoxide dismutase (SOD); and glutathione peroxidase (GPx). These exhibited significant changes in birds during the migratory phase, as Valeria Marasco explains: “We found that the emergence of the migratory phenotype was associated with higher TBARS in the liver, lower SOD values in red blood cells, higher GPx in the pectoral muscle, and changes in red blood cells and the liver.”

Pectoral muscles protected from oxidative stress

However, the researchers found no link between food intake and variation in markers of oxidative status in any of the tissue examined, despite food intake being higher in the migratory birds. However, the increase in body mass was positively correlated with muscle GPx activity as birds entered the pre-migratory fattening phase,  while the amount of decrease in body mass was negatively correlated with muscle GPx as birds transitioned to the non-migratory phase. Such correlations were absent in red blood cells and liver. Marasco: “Our work suggests that during the emergence of the migratory phenotype birds might strategically displace oxidative costs on the liver in order to safeguard the pectoral muscles, which play a fundamental role in the successful completion of the migratory flight.”

Sex-specific differences in one marker of oxidative stress

The researchers conclude that their study, which was recently published in the Journal of Experimental Biology, provides novel and clear evidence that birds undergo tissue-specific changes in oxidative status during their transition to the migratory and the non-migratory state. According to the researchers, future studies with different bird species in the wild, ideally under a naturally varied diet, are now needed to validate the assumption that migratory birds strategically protect their flight muscles from detrimental increases in oxidative damage and so improve their fitness during migration. The data on GPx also suggest sex-specific differences in the migratory phase in the red blood cells and liver. Further studies are needed to explore whether these sex-specific differences are functionally linked with markers of oxidative stress.

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