The role of ketogenesis in the migratory fattening of the northern wheatearOenanthe oenanthe

Abstract

The fuelling capacity of migratory birds and their ability to avoid health conditions derived from the subsequent fat overload are exceptional among vertebrates. In this work, we screen the expression of the genes involved in the production of ketone bodies (KB) in the liver of northern wheatears ( Oenanthe oenanthe ) during the development and resolution of migratory fattening. Thirteen genes were found to be regulated among the migratory stages. Based on the dynamics of gene expression, we concluded that KB play a versatile role in wheatears' energy metabolism homeostasis. The ketogenic pathway can adaptively: (i) provide carbon equivalents for lipogenesis, speeding up fuelling; (ii) replace glucose during long-distance flights using lipids as the substrate; (iii) act as a floodgate to avoid steatosis; and (iv) might provide a metabolic solution to defatting in captive birds.

Flexibility underlies differences in mitochondrial respiratory performance between migratory and non-migratory White-crowned Sparrows (Zonotrichia leucophrys)

“…Similarly, β-hydroxybutyrate was also elevated only during migration, indicating that the availability of ketone bodies was high during migration in Gambel’s individuals but low during the non-migratory period. Frias-Soler et al showed that 13 different genes regulating ketogenesis are differentially expressed relative to migratory status in the migratory Northern Wheatear ( Oenanthe oenanthe ) 26 providing added support for the hypothesis that ketone bodies are vital for pre-migratory fattening and long-distance migratory flight.…”

“…To test whether individuals in the Gambel’s population possess a high capacity to deliver oxygen and energy to the mitochondria, as is observed in other migrants, we measured hematocrit and hemoglobin. We used hematocrit as a proxy for oxygen-carrying capacity, β-hydroxybutyrate as a measure of ketone bodies supplied to flight muscles, which appears to be an important replacement for glucose while fasting 26 , and citrate synthase as a proxy for mitochondrial volume. Because hematocrit and hemoglobin have been shown to be persistently different between migrants and non-migrants, while migrants display within-population flexibility between the migratory and non-migratory period 3 , 13 , we predicted that hematocrit, hemoglobin, and citrate synthase would be higher in Gambel’s than Nuttall’s White-crowned Sparrows.…”

“…In contrast, we predicted that these variables would be consistent throughout the year in Nuttall’s individuals and similar to Gambel’s individuals during the non-migratory period. β-hydroxybutyrate is known to increase in response to the intense demands of migratory flight 26 , and thus, this ketone body is expected to be high only during migration in Gambel’s individuals.…”

Seasonal plasticity and energy efficiency in migratory buntings is an assemblage of alterations in metabolic and gut microbe adaptations

“…Migratory birds adopt strategies to accumulate and switch energy substrates, expedite lipogenesis, and transport fatty acids to muscles to achieve continuum of extreme metabolic transitions from nonM, preM, M up to posM , while limiting unfavourable metabolic consequences (Mcfarlan, 2009; Guglielmo, 2010). For example, during migration, hyperglycaemic (Szwergold, 2014) northern wheatears’ adaptively replace glucose with lipid substrates to improve energy homeostasis, whereas in captive birds gives metabolic solution to defatting (Frias-Soler et al, 2021). Tiny Ruby-throated hummingbird are reported to avoid glucosuria through higher turnover rates of red blood cells and proteins (Hargrove, 2005).…”