Summer dormancy in edible dormice (Glis glis) without energetic constraints

Abstract

Average longevity in free-living edible dormice (Glis glis) can reach 9 years, which is extremely high for a small rodent. This remarkable life span has been related to a peculiar life history strategy and the rarity of reproductive bouts in these seed eaters. Most females (96%) reproduce only once or twice in their lifetime, predominantly during years of mast seeding of, e.g., beech, but entire populations can skip reproduction in years of low seed availability. Surprisingly, in non-reproductive years, large fractions of populations apparently vanished and were never captured above ground. Therefore, we determined the duration of above-ground activity, and body temperature profiles in a subset of animals, of dormice under semi-natural conditions in outdoor enclosures. We found that non-reproductive dormice returned to dormancy in underground burrows throughout summer after active seasons as short as <2 weeks. Thus, animals spent up to >10 months per year in dormancy. This exceeds dormancy duration of any other mammal under natural conditions. Summer dormancy was not caused by energy constraints, as it occurred in animals in good condition, fed ad libitum and without climatic stress. We suggest that almost year-round torpor has evolved as a strategy to escape birds of prey, the major predators of this arboreal mammal. This unique predator-avoidance strategy clearly helps in explaining the unusually high longevity of dormice.

Seasonality of torpor patterns and physiological variables of a free-ranging subtropical bat

“…This suggests that N. bifax, like N. geoffroyi, is reducing MR and T b significantly more during these short bouts of hibernation in comparison to the shallow torpor bouts seen in daily heterotherms, thus maximising energy savings (Geiser and Brigham, 2000;Geiser, 2004). Our current study and preliminary data that show MR are similar in both seasons (C. S., unpublished data) provide further support for the argument that, apart from the observed temperature effects, there is no apparent functional difference between the physiology of prolonged and short bouts of torpor of hibernators, which are capable of showing both (Hock, 1951;Geiser and Brigham, 2000;Bieber and Ruf, 2009). N. bifax, like many other species of bats and other mammals, appear to be 'opportunistic hibernators' and make use of increased food availability during occasional increases in T a during winter and enter prolonged bouts of torpor when conditions are unfavourable (Körtner and Geiser, 2000b).…”

“…In the subtropical winter even when T a was variable and much warmer than in temperate winters, N. bifax entered prolonged torpor bouts (up to 128.5h) regularly which clearly classify them as 'hibernators' (Geiser and Ruf, 1995;Schmid and Ganzhorn, 2009). Consequently, the short bouts of torpor observed in our study during summer, as found for dormice, most likely are short bouts of hibernation, which simply are shortened because of high and fluctuating T a , rather than daily torpor (Geiser, 2004;Bieber and Ruf, 2009). This suggests that N. bifax, like N. geoffroyi, is reducing MR and T b significantly more during these short bouts of hibernation in comparison to the shallow torpor bouts seen in daily heterotherms, thus maximising energy savings (Geiser and Brigham, 2000;Geiser, 2004).…”

Seasonal variation in telomere length of a hibernating rodent

“…The mean RTL of our study population remained largely unchanged over the winter hibernation season, whereas over the active season, telomeres shortened in sub-adults, but lengthened in adults. At the individual level, variation in posthibernation RTL was partly explained by the reduction in body mass over the period of inactivity, which we know is a positive linear function ( p ¼ 0.003) of time spent euthermic during hibernation in our captive population of edible dormouse [17]. These results for a hibernator, therefore, agree with our previous findings for daily torpor in the Djungarian hamster, Phodopus sungorus [8], that torpor use is positively related to the change in telomere length over winter.…”

Torpor in Dark Times: Patterns of Heterothermy Are Associated with the Lunar Cycle in a Nocturnal Bird

“…3 predation risk or variable environmental temperatures) might also be important determinants of heterothermy in endotherms (Bieber and Ruf 2009;Mzilikazi et al 2002;Stawski and Geiser 2010;Warnecke et al 2008). Efforts have been made to generalize all factors affecting the expression of T b , whether well studied or not, into an adaptive framework (Angilletta et al 2010;Humphries et al 2003).…”