Abstract
Fatty acids (FA) have crucial functions in animals, affecting e.g. inflammatory responses, thermoregulation, and cell membrane fluidity. Diet and ambient temperature affect animals’ FA composition, which, in turn, may influence these physiological processes. Great tits (Parus major) −common in both urban and rural habitats− are mainly granivorous during winter and insectivorous during summer. These diets show pronounced differences in FA composition. Such variation has context-dependent effects on physiology, because the thermal environment, food availability, and levels of pro-inflammatory environmental stressors differ between urban and rural areas. Thus, we investigated how great tit plasma FA composition varied between urban and rural habitats and across seasons. Eight FAs differed between urban and rural birds. Among these, arachidonic acid (omega (ω)-6 polyunsaturated FA) with thermoregulatory and pro-inflammatory properties was more abundant in urban than rural birds in winter, whereas ω-3 FAs with anti-inflammatory properties were more abundant in rural birds. The difference in pro- and anti-inflammatory FAs suggest that the negative health effects that urban birds suffer from being exposed to higher levels of pollutants might be enhanced by an elevated inflammatory response. Eight FAs differed between winter and summer birds. This variation reflected the diet change: FAs common in seeds, e.g. oleic- and linoleic acid, were present in higher amounts in winter birds, whereas ω-3 polyunsaturated FAs that are common in caterpillars were more abundant in summer birds. Overall, a larger seasonal variation was seen among the urban birds. This study is the first to reveal a difference in FA composition between urban and rural populations for all animals studied to date. Future experiments should unravel the physiological implications of this variation, and ultimately, link its effects to fitness of animals with different physiological and dietary requirements in ur
Highlights
Urbanization is a global concern for the health and persistence of many wild animal populations
We demonstrate that most fatty acid (FA) with known physiological functions differ in relative abundance in great tit plasma between birds from urban and rural habitats and on a seasonal basis
Seasonal Variation (Predictions I–IV) The relative amount of eight of the nine analyzed FAs in great tit blood plasma differed between seasons in both urban and rural habitats
Summary
Urbanization is a global concern for the health and persistence of many wild animal populations. What is perhaps less known is the impact of diet and ambient temperature on the fatty acid (FA) composition of animal tissues, which is important for a wide range of physiological processes including oxidative stress, inflammation, thermoregulation, exercise performance, and cell membrane fluidity (Hazel, 1995; Larsson et al, 2004; Pierce et al, 2005; Ben-Hamo et al, 2011; Hulbert and Abbott, 2012) These physiological processes, in turn, are affected by or regulated in response to extrinsic stressors, such as pollutant levels, pathogen infections, and temperature, which all vary on both temporal (e.g., between seasons) and spatial (e.g., between urban and rural habitats) scales (Tinoco, 1982; Hulbert and Else, 1999; Larsson et al, 2004; McWilliams et al, 2004; Cherian et al, 2009; Hulbert and Abbott, 2012). By studying variation in animal FA content across habitats and seasons, we can gain insights into variation in animals’ diets and pinpoint individual FAs that might constrain or facilitate any context-dependent physiological responses to the environment
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