Konsequenzen von Landschaftsfragmentierung für life history Strategien bei Säugern und deren zugrunde liegenden ökophysiologischen Wirkungsmechanismen
Final Report Abstract
The performance of wild animals is impacted by diverse and co-occurring challenges, which might ultimately affect their reproductive success and survival. The investigation of physiological responses to these challenges may be the key to elucidate mechanisms that contribute to variations in fitness parameters. In this study we investigated morphometric, demographic and physiological changes in small arboreal mammals, Glis glis and Muscardinus avellanarius, associated with habitat fragmentation, resource availability, hibernation and reproductive activity and consequences of these changes for their fitness. Another focus of our research deals with the potential role of hibernators for the transmission cycle of Lyme-disease spirochetes. Our population genetic analyses revealed that edible dormice (G. glis) inhabiting forest fragments were genetically isolated from each other. This is comparable to the situation of populations occurring on oceanic islands, where individuals were shown to systematically differ in their demography, metabolic physiology, and body size, when compared to their mainland counterparts. In accordance with patterns described by the “island rule” for small mammals, individuals of both dormouse species were larger and more numerous within forest fragments. These high population densities can assumed to be associated with strong intraspecific competition for limited resources and mating partners and may therefore represent a stressful situation. However, we could not detect increased stress hormone levels, stress-induced alterations in immune cell counts or the oxygen transport system, in individuals of high density populations. Individuals of both dormouse species further showed higher resting metabolic rates and lower rates of torpor, if inhabiting isolated forest patches, which stands in contrast to general patterns described before. High population densities, increased body sizes, lowered metabolic rates and reduced stress levels observed in forest fragments, might possibly explained by a relaxed predation pressure within forest fragments. The physiologically most efficient way to reduce energy consumption and to survive periods of unfavorable environmental conditions is to enter hibernation. An extreme leukopenia and drastically compromised functionalities of basically all immune system components represent the typical epiphenomenon of hibernation, all of which were generally found to revert immediately upon arousal. Surprisingly, our study revealed that hibernation results in depleted phagocyte (neutrophils and monocytes) stores, whereas lymphocytes constituted high counts throughout the entire active season. Hence, the post-hibernation leukocyte pattern of the innate immune system described in our study differs distinctively from those found so far in all other hibernators investigated and strongly suggests that the first line of defense against pathogens is impaired upon and after emergence. This impairment coincides with lowest survival probabilities during the annual cycle of our study species and might represent an important cost of hibernation also for other hibernating species. Edible dormice show an extreme flexibility in metabolic and thermoregulatory behaviour, which seems to be an important adaptation for exploiting irregularly occurring food resources and surviving extended periods of fasting. Low stress hormone levels during extended fasting periods demonstrate that they do not impose considerable stress on our study species, possibly because these periods are predictable and edible dormice are perfectly adapted to reduce energy consumption under energetically challenging situations. Haematological investigation further revealed that under limited food availability the rate of erythrocyte generation was low, which seems to be part of an energy saving strategy. High survival rates detected during low mast years support this assumption. During reproduction edible dormice exhibit strongly elevated stress hormone levels, leading to characteristic impairments of the immune and the oxidative transport system. These stress responses may represent part of the reproductive costs dormice incur and explain reduced survival rates during high reproductive years. Surprisingly, our results further suggest a loss of infection with Lyme disease spirochetes during the hibernation season in edible dormice. Thus the seasonality of the prevalence of LD spirochetes in edible dormice was pronounced and shows that metabolic physiology may generally affect the role of hibernators as reservoir hosts for zoonoses.
Publications
- (2012) Stranded on an island: consequences of forest fragmentation for body size variations in an arboreal mammal, the edible dormouse (Glis glis). Population Ecology 54(2):313-320
Fietz J, Weis-Dootz T
(See online at https://doi.org/10.1007/s10144-012-0310-0) - (2014) Genetic consequences of forest fragmentation for a highly specialized arboreal mammal - the edible dormouse. PLoS One 9(2):e88092
Fietz J, Tomiuk J, Loeschcke V, Weis-Dootz T, Segelbacher G
(See online at https://doi.org/10.1371/journal.pone.0088092) - (2014) Seasonal prevalence of Lyme disease spirochetes in a heterothermic mammal, the edible dormouse (Glis glis). Applied and Environmental Microbiology 80(12):3615-3621
Fietz J, Tomiuk J, Matuschka F-R, Richter D
(See online at https://doi.org/10.1128/AEM.00251-14) - (2014) Ways to measure body temperature in the field. Journal of Thermal Biology 42:46-51
Langer F, Fietz J
(See online at https://doi.org/10.1016/j.jtherbio.2014.03.002) - (2016) It takes two to tango: Phagocyte and lymphocyte numbers in a small mammalian hibernator. Brain, Behavior, and Immunity 52:71-80
Havenstein N, Langer F, Stefanski V, Fietz J
(See online at https://doi.org/10.1016/j.bbi.2015.09.018) - (2016) The vector tick Ixodes ricinus feeding on an arboreal rodent—the edible dormouse Glis glis. Parasitology Research:1-8
Fietz J, Langer F, Havenstein N, Matuschka F-R, Richter D
(See online at https://doi.org/10.1007/s00436-015-4877-1)
