Scientists at the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) and Helmholtz Munich have now demonstrated that fatty acid oxidation plays a key role in the metabolism of some bats. By measuring metabolic by-products in the bats’ blood, they found that fatty acid oxidation is particularly important during migration in Nathusius' pipistrelles. The findings have been published in the journal The FASEB Journal.
For the study, the research team led by Alesia Walker (Helmholtz Munich), Shannon Currie and Christian Voigt (both Leibniz-IZW) analysed blood samples from Nathusius’ pipistrelles (Pipistrellus nathusii) that had flown in a wind tunnel under controlled conditions, as well as from wild individuals of the same species during the migration and non-migration seasons. The bats studied were captured at the Engure and Pape ornithological research stations in Latvia. Using specialised chromatographic methods (hydrophilic interaction chromatography/ ultra-high-performance liquid chromatography, HILIC/UHPLC), the scientists searched for polar metabolites and fats (lipids) within the blood of bats immediately after flight, and after a one-hour recovery period. Data were collected from 16 individuals that flew at constant speeds for 30 minutes in a wind tunnel at Lund University, and a further 47 individuals captured during their nightly flights in the wild.
Bat migration is enabled by high rate of fatty acid oxidation
Analysis of the metabolites provided clear evidence of the significant role played by fatty acid oxidation during migration. When bats are in flight for longer periods, for example, levels of acyl carnitines in the blood are elevated by around 70%. Acyl carnitines are the transport form of fatty acids as they are shuttled into the mitochondria (the cells’ ‘powerhouses’), where they are oxidised (burnt) to produce energy. Without the transport molecule carnitine, the mitochondrial membrane would be impassable for fatty acids. Furthermore, the scientists observed significantly higher levels of phosphatidylethanolamines with unsaturated fatty acids, as well as several phosphatidylcholines, in the bats sampled during the migration period compared to bats that had not yet migrated.
“We were able to demonstrate that the products of lipid metabolism were significantly elevated during the migration of Nathusius’ pipistrelles. This contradicts the established view that mammals have only limited capacity to transport and oxidise fatty acids during periods of intense activity”, explains Dr Alesia Walker, senior scientist in the Department of Analytical Biogeochemistry at Helmholtz Munich. “This applies in particular to the metabolites of unsaturated fatty acids, whilst the metabolites of saturated fatty acids show no significant differences between migrating and non-migrating bats.” Like all mammals, bats cannot synthesise polyunsaturated fatty acids themselves and must derive them through their diet. During the migration season, Nathusius’ pipistrelles feed primarily on aquatic or riparian insects. These are often richer in long-chain, polyunsaturated fatty acids than forest-dwelling insects.
Physiological adaptations of bats to seasonal migration are similar to those of birds
“Our findings show how Nathusius’ pipistrelles gear up their metabolism for the long migration to their winter roosts by burning fatty acids,” says Prof Dr Christian Voigt, Head of the Department of Evolutionary Ecology at the Leibniz-IZW. “Just like other mammals, we humans are not capable of doing this to the same extent, because during periods of intense exertion we can only meet our high energy requirements to a very limited extent by burning fatty acids. When we exercise, our body provides the necessary energy mainly from glycogen, a stored form of carbohydrates.” When glycogen stores are depleted during training or competition, the body does not have enough energy to sustain the same level muscle activity. This can lead to a drop in performance and rapid fatigue. Many athletes recognise this phenomenon as ‘hitting the wall’.
Given that Nathusius’ pipistrelles migrate seasonally over several thousand kilometres between their summer habitats in north-eastern Europe and their winter habitats in western and southern Europe, such a drop in performance would be fatal. “Bats therefore perform to some extent like birds and are able to sustain high levels of performance through the oxidation of fatty acids,” concludes Voigt. This means that, theoretically, like many European songbirds, they could even migrate further, as far as Africa. “However, they do not do so, quite simply because they do not need to: bats hibernate for several months in their winter quarters, something birds cannot do. The Nathusius’ pipistrelle, for example, can easily survive the winter in the Mediterranean region and does not need to migrate to even warmer climes.”
