Composition of physiologically important fatty acids in great tits differs between urban and rural populations on a seasonal basis

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 urban and rural environments.

Species-Dependent Effects of the Urban Environment on Fatty Acid Composition and Oxidative Stress in Birds

“…Fatty Acid Extraction and Gas Chromatography/Mass Spectrometry (GC/MS) Analysis Fatty acids were extracted following the protocol described in Andersson et al (2015). Briefly, a total lipid extraction of 5 µl plasma was performed for 1 h at room temperature using 50 µl chloroform:methanol (2:1 v/v).…”

“…the total ω-6/ω-3 PUFA ratio, lipid peroxidation susceptibility index (peroxidation index, PI; Pamplona et al, 1998;Kang et al, 2004), and lipid peroxidation (malondialdehyde, MDA), differed between the urban and rural individuals of the four species (Gutteridge, 1995). We predicted (3) that urban birds should have a lower overall proportion of both ω-6 and ω-3 PUFAs, but due to the even lower availability of ω-3 PUFAs (compared to ω-6 PUFAs) in the urban habitat (Andersson et al, 2015;Toledo et al, 2016), we expected to find an increase in the ω-6/ω-3 PUFA ratio in urban birds. We also predicted (4) that the adapter species would show a more pronounced difference between the urban and rural environments, given that the exploiter species rely on human-provided foods also in the rural habitat.…”

“…For example, while species in their natural environments have evolved unique feeding niches, interspecific dietary differences tend to converge in urban areas due to superabundance of human-provided food items (e.g., sunflower seeds, peanuts, bread, tallow, coconut fat, and leftovers; Jones and Reynolds, 2008). Such food items have a different, potentially poorer, nutrient composition compared to natural food sources (Schoech and Bowman, 2003;Schoech et al, 2004;Jones and Reynolds, 2008;Andersson et al, 2015). Reliance on (exploiters), or high intake of (adapters), human-provided food may therefore further reduce individual health and reproductive success in urban birds.…”

“…Reliance on (exploiters), or high intake of (adapters), human-provided food may therefore further reduce individual health and reproductive success in urban birds. Moreover, natural food sources in urban areas can also be of poorer quality than those in rural areas, which contributes to the lower availability of important macro-and micro-nutrients in cities (Isaksson and Andersson, 2007;Møller et al, 2010;Andersson et al, 2015;Isaksson et al, 2015).…”

“…The composition of fatty acids (FAs) has been suggested to differ between anthropogenic and natural food sources (Andersson et al, 2015), but FA variation has rarely been investigated in this context. FAs are obtained via dietary sources, or by de novo biosynthesis.…”