Many species of bats migrate long distances, but the physiological challenges of migration are poorly understood. We tested the hypothesis that migration is physiologically demanding for bats by examining migration-related phenotypic flexibility. Both bats and birds are endothermic, flying vertebrates; therefore, we predicted that migration would result in similar physiological trade-offs. We compared hoary bats (Lasiurus cinereus) during spring migration and summer non-migratory periods, comparing our results with previous observations of birds. Migrating bats had reduced digestive organs, enlarged exercise organs, and fat stores had higher proportions of polyunsaturated fatty acids (PUFAs). These results are consistent with previous studies of migrating birds; however, we also found sex differences not typically associated with bird migration. Migrating female hoary bats increased the relative size of fat stores by reducing lean body components, while males maintained the same relative amount of fat in both seasons. The ratio of n-6 to n-3 PUFA in flight muscle membrane increased in migrating males and decreased in migrating females, consistent with males using torpor more frequently than females during spring migration. Enlarged exercise organs, reduced digestive organs and changes in adipose tissue composition reflect the elevated energetic demands of migration. Sex-specific patterns of fat storage and muscle membrane composition likely reflect challenges faced by females that migrate while pregnant. Our results provide some of the first insights into the physiological demands of bat migration and highlight key differences between bats and birds.
We gratefully acknowledge funding for this study provided by Bat Conservation International (student scholarship to L.P.M.), the Society for Integrative and Comparative Biology (travel fellowship to L.P.M.), the University of Western Ontario (research grant to L.P.M.) and the Natural Sciences and Engineering Research Council of Canada (Discovery grants to C.G.G. and M.B.F.). L.P.M. was supported by a Canada Graduate Scholarship from the Natural Sciences and Engineering Research Council of Canada.
LIST OF SYMBOLS AND ABBREVIATIONS
- double bond index
- fatty acid
- fatty acid methyl ester
- monounsaturated fatty acid
- non-esterified fatty acid
- neutral lipid
- principal component
- principal components analysis
- polyunsaturated fatty acid
- © 2013. Published by The Company of Biologists Ltd