| Summary: | According to life history theory individuals will optimize investment into growth, reproduction and self-maintenance. Egg size is an important life history trait predicted to have an optimum that maximizes maternal individual fitness. Bet-hedging theory suggests that natural selection in addition to act on the mean of egg size also will act on the variance of egg size. Studies in several taxa have demonstrated a great variation where some studies have found evidence for an optimum egg size but others not. In a metapopulation of house sparrows (Passer domesticus) in northern Norway this study aimed to investigate the effects of variation in egg size on maternal individual fitness. Maternal individual fitness was defines as the sum of annual survival and half the number of recruits produced. The most central findings revealed i) no effect of mean egg size on short- and long term production of offspring, maternal survival and maternal individual fitness. ii) There was a positive effect of temperature during nestling period and a negative effect of within brood variation in egg size on fledgling production, but not on long-term recruit production. Finally, iii) an effect of maternal mass on recruit production, maternal survival and maternal individual fitness, depending on the number of broods laid. This study highlight the importance of taking maternal ecology in to account, and calls for further investigation of the effect of maternal quality including body mass and the investment in the number of broods laid and how this affects maternal fitness.
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