Thermal preference and hibernation period of Hodgson's bats (Myotis formosus) in the temperate zone: How does the phylogenetic origin of a species affect its hibernation strategy?

Hibernation is regarded as a physiological and behavioral adaptation that permits the survival of animals such as bats during seasonal periods of energy shortage. Moreover, the phylogenetic history of a species can be used to investigate the evolution of its thermal regulation system during torpor. Hodgson's bat (Myotis formosus (Hodgson, 1835)) is a temperate species that arose phylogenetically from an Ethiopian lineage, suggesting that this bat lineage secondarily colonized a temperate climate. Therefore, the hibernation pattern of M. formosus may differ from that of other temperate bat species. This study investigated the hibernation period of M. formosus in the temperate climate zone and the relationship between thermal preference and hibernating process of bats. Myotis formosus hibernated in roosts maintained in warm (temperature, 12-14 °C) and humid (relative humidity, >95%) ambient conditions. The bats began to hibernate in early October and final arousals occurred in mid-May so that the total length of the hibernation "season" was 220 days. The period of hibernation was strongly influenced by fluctuations in the external minimal temperature. Most bats entered the hibernacula when the external minimal temperature was lower than the temperature of the hibernacula (mean, 13 °C) and emerged from the hibernacula when the external temperature exceeded the temperature of the hibernacula. This study suggests that the onset and termination of M. formosus hibernation is due to the interaction between the temperature of the hibernacula and that of the external environment and is based on the thermal preference of the bats. The study also suggests that the hibernation strategy of this species may be a product of its phylogenetic origin as a tropical bat species adapting to a severely cold climate.