THE INFLUENCE OF SPRING TEMPERATURE ON THE INTENSITY OF ADVERTISING BEHAVIOR AND BASAL METABOLIC RATE IN BRIGHT AND PALE PIED FLYCATCHER (FICEDULA HYPOLEUCA) MALES

Polymorphic species hold a special attraction due to the ability of their populations to evolve rapidly in response to stable environmental changes, e.g. climate change. Two remote populations of the pied flycatcher (Ficedula hypoleuca), a species with polymorphism in breeding plumage of males, were used in this work. A response of differently colored males to changes in ambient temperature during the period of mate choice was estimated. Males of the pale phenotype rapidly reduced the intensity of advertising behavior in response to cold temperature in both populations of Tomsk and Moscow regions. The activity of bright males remained high within a broad range of ambient temperatures. In the experiments on mate choice, females preferred males with high intensity of advertising behavior: the coloration type per se was not of importance. When temperatures fell, females chose bright males because they were tolerant to cold. In the experiments on short-term acclimation of birds from a natural population at 3-5 degrees C and 22-25 degrees C, pale males, in contrast to bright ones, increased their basal metabolic rate (BMR) in response to cold. Pale males are suggested to gain physiological resistance to the cold due to the increase in BMR, but they have to cut down energetic expenses on reproductive behavior, which adversely affects their mate prospects. In spite of the similar temperature response in the birds from two regions, spring temperatures had radically different impact on the phenotypic balance in these populations. In the Tomsk population, where bright males are scanty, their proportion many times increased in the years with the coldest springs as consistent with our experiments. There was no such effect in the Moscow population. The nature of the differences between two populations Of pied flycatchers is discussed.