Do greater mouse-eared bats experience a trade-off between energy conservation and learning?

Bats, some species of rodents and some birds are able to save energy during the summer period by decreasing their body temperature and falling into torpor. Some studies indicate that torpor prevents sleeping and causes effects similar to sleep deprivation. Impairment of processes stabilizing memory slows down learning accuracy and speed. We conducted two experiments to test whether greater mouse-eared bats, Myotis myotis, which commonly use torpor during the summer period, experience a trade-off between energy savings and learning abilities. We compared learning speed and accuracy in bats that were exposed to low (7 degrees C) and higher ambient temperatures (22 degrees C) between training and experimental sessions. Tests were conducted in experiments with food reward (food search) and without food reward (perch search). Time spent with the skin temperature above 30 degrees C was significantly longer for bats exposed to 22 degrees C than for those exposed to 7 degrees C, and longer in experiments with food reward than without food reward. We observed only a very weak tendency for better accuracy and shorter search times in bats exposed to 22 degrees C than in those exposed to 7 degrees C. Our data indicate that memory consolidation of bats under natural conditions is not affected by daily torpor when bats are in good condition and may therefore defend against a rapid fall into torpor. We suggest that homeostatic processes connected with the circadian rhythm allow protection of the consolidation of memory for relatively simple tasks despite time spent in torpor.