Teresa G. Valencak University of Veterinary Medicine Vienna, Research Institute of Wildlife Ecology, Vienna, A Title Fats you need: Membrane Fatty Acids and their Relation to Cold Adaptation, Metabolic Rate and Lifespan Abstract Polyunsaturated fatty acids (PUFAs) are essential components that confer fluidity and selective permeability to biological membranes, both as major constituents of phospholipids, and as regulators of membrane- associated enzymes. Numerous papers in the last decade have explored the influence of polyunsaturates on hibernating mammals but the role of PUFAs for terrestrial, nonhibernating mammals has rarely been investigated so far. We indeed found out that European brown hares show a seasonally different pattern in muscle phospholipid fatty acid composition with peak membrane unsaturation in winter. Apart from their role for cold adaptation, certain membrane PUFAs, especially the very long-chain ones, are said to raise basal metabolic rate (BMR) in mammals. Support for that originates in the systematic variation among mammalian species with those mammals having high BMRs also having high contents of membrane PUFAs. To that fits the assumption that high contents of membrane unsaturated fatty acids shorten lifespan as PUFAs are prone to peroxidation processes thus could increase the production of radical oxygen species (ROS). However, two major problems arise with these simple correlations between membrane fatty acid composition, metabolism, and longevity. Firstly, the problem of not accounting for body weight and secondly, species in comparative data sets may not represent independent replicates and thus could compromise the results. By counting on a large dataset and on both multivariate conventional and phylogenetic regression we surprisingly found no correlation between particular fatty acids and BMR. Interestingly however, maximum lifespan significantly decreased as a certain class of phospholipid PUFAs (namely n-3 PUFAs) increased. CV Professional experience 2002- present: PhD at the Research Institute of Wildlife Ecology, Veterinary University Viennasince 2004: Correspondent for "Outside JEB", Journal of Experimental Biology 2002: M.Sc.in Zoology, University of Vienna 2001-2002: Thesis "The influence of fatty acids on cold adaptation in the European Brown Hare (Lepus europaeus)" 1996- 2001: Study of Biology, University of Vienna; main subject: zoology, optional subject: parasitology 1996: Matura degree in Linz, Austria Selected recent publications Valencak TG, Ruf T (2006) N-3 polyunsaturated fatty acids impair lifespan but have no role for metabolism. Aging Cell (in press). Valencak TG, Arnold W, Tataruch F, Ruf T (2003) High content of polyunsaturated fatty acids in muscle phospholipids of a fast runner, the European brown hare (Lepus europaeus). Journal of Comparative Physiology B 173: 695-702. Valencak TG (2002) The influence of fatty acids on cold adaptation in the European Brown Hare (Lepus europaeus), Thesis, University of Vienna, 53 pp. Institution address Teresa G. Valencak Research Institute of Wildlife Ecology Savoyenstraße 1 1160 Vienna Austria phone: 4890915 - 151 fax: 4890915 - 333 Teresa.Valencak@vu-wien.ac.at http://www.vu-wien.ac.at/i128/tel.htm or http://www.fiwi.at