The effects of spatial and temporal ecological variation on fatty acid compositions of wild great tits Parus major

In birds, fatty acids (FA) have three main functions; they are structural components of cell membranes, metabolic fuel, and inflammatory molecules. Environmental factors, such as diet and ambient temperature, affect FA composition, thereby function and ultimately fitness. Thus, variation in FA compositions can be the underlying mechanism for varying performance of birds in different habitats. Here we examine variation in plasma FA composition in nestling and adult great tits Parus major, between 1) deciduous and coniferous, and 2) sun-exposed and shaded habitats. The main results revealed that nestlings had a higher proportion of -linolenic acid (-LNA) in deciduous habitats and arachidonic acid in coniferous habitats. This reflects a difference in caterpillar availability between habitats with the deciduous habitat being caterpillar-rich, whereas the coniferous habitats are rich in spiders. In addition, -LNA increased with nestling body condition in the coniferous habitat, supporting the importance of caterpillars for fledging success in this species. In line with dietary intake, the proportion of the essential -LNA and linoleic acid (LA) increased over the course of the day for all birds. In the deciduous habitat, adult females showed a positive association between LA and body condition. Furthermore, habitat sun-exposure showed significant interactions with body condition for polyunsaturated FAs in nestlings, and with saturated FA in adult males, which is in accordance with the homeoviscous hypothesis stating that the proportion of saturated FA should decrease with decreasing ambient temperature. Taken together, small-scale heterogeneity in habitat structure significantly influences FA compositions of great tits. Many of the results can be linked to dietary, and possibly, ambient temperature differences between habitats. These habitat effects on FA compositions can lead to different capacities of individual birds to deal with infections and low temperatures, two stressors that cause major mortality among wild birds.