Seasonal Migrations of Hoary Bats

Migrations require energy that animals get from resourcing their metabolic fuels. Bats are mammals that make their migratory journeys through flight like birds. Since fat has more energy per unit mass, birds use this as their means for enduring long migrations. It was hypothesized that due to evolutionary convergence bats would use fat stores similar to birds as fuel. Hoary bats (Lasiurus cinereus) would accomplish this through their oxidation pathways and fatty acid transport proteins (names) being seasonally upregulated in their flight muscles. The objective of this paper is to better understand how hoary bats are capable of sustaining a level of endurance that is required during their seasonal migrations.

Observations were made through collecting 8 female and 7 male non-migratory bats and pups between July 20-August 1, 2018 in Cypress Hills Interprovincial Park, Saskatchewan, Canada. 15 female and 15 male migratory bats were captured using mist nests in Bernalillo County, New Mexico and in Manzano Mountains, Cibola National Forest, New Mexico on May 5 through May 17, 2009. The bats were euthanized and their pectoralis muscles were dissected and stored at −80 °C. After preparing the tissue through RNA isolation and reverse transcription into cDNA, primers were made for target genes H-FABP, FABPpm, and FAT/CD36. H-FABP transports fatty acids from the cell membrane into the mitochondria, therefore this would increase in hibernating bats because they solely rely on stored fats during hibernating periods. FABPpm, and FAT/CD36 transport the fatty acids into the muscle cells and is upregulated in migrating sparrow birds. After the hoary bat sequence was found, PCR was performed.

By using birds as a model system predictions can be made. 3-hydroxylacyl-Coa dehydrogenase (HOAD), carnitine palmitoyltransferase (CPT), and citrate synthase (CS) are oxidative enzymes whose levels vary seasonally in birds. This should lead to an increase of these three enzymes in migrating bats.

Results showed that the target gene H-FABP increased expression 5 times for migrating females, indicating a variation among sex. Females may require extra fat in order to reach the destination faster before giving birth, or may need the extra energy to find the appropriate location to give birth. There was a 32% increase in CPT, 29% increase in CS, and 53% increase in HOAD. Males displayed a greater HOAD percent, but CS and CPT were not affected by sex differences. During spring migration the bats aerobic capacity increased and a higher demand for fatty acids was required from possibly a greater demand physiologically from the bats.

I found that this paper presented a clear hypothesis but did not include any data on female bats or their pups. This could be due to lactating females having a different metabolic rate due to pregnancy and sub-adults having a faster metabolism. If this were the case inconclusive data would have been presented. The study found that bats do not increase their fatty acid protein levels like birds. Bats may have found other ways to deal with the strains that occur during migration. Bats feed and migrate at the same time unlike birds that fly at night and feed during the day. Since bats do not feed during the day they shut off their metabolism and this can save them a lot of energy.