ИСТИНА

In Pied Flycatchers (Ficedula hypoleuca), father’s basal metabolic rate (BMR) and offspring resting metabolic rate (RMR) were found to be positively related (Bushuev et al., 2003). Recent cross-fostering experiments assumed the existence of heritability of resting metabolic rate in Pied Flycatcher (Bushuev et al., in press). To consider the problem more fully, we studied sexual differences of fledglings in energetics. RMR of fledglings, which reached asymptotic body mass (13-15 days old), was measured by oxygen consumption at nighttime and its estimates were expressed as body mass residuals. Sex identification of monomorphic fledglings was based on analysis of DNA (Kahn et al., 1998) extracted from blood samples (n = 79 from 40 broods). On average, male and female fledglings did not differ in body mass and wing length, but tarsus was longer in females than in males. RMR of male fledglings was higher than that of female ones, and this difference was more pronounced among offspring of old (>= 2 ys) males (ANOVA: F=9.6; p=0.003; n=50). Sexual asymmetry in energetics of fledglings appeared to be unrelated to variation in growth rate and may reflect the superiority of male fledglings in such components of RMR as basal metabolism. The opposite trend was demonstrated by adults during the period of rearing chicks: BMR of females was significantly higher than that of males (n=137). Possible functional consequences of sex-dependent differences in resting metabolism will be discussed.