Maternal effects and female egg allocation strategies

The study of maternal effects has experienced an extraordinary development in the last decade. Evolutionary biologists no longer consider maternal effects as "troublesome sources of environmental resemblance", but rather as mechanisms that can generate adaptive phenotypic plasticity at the heart of evolutionary responses to natural selection. One important property of maternal effects is that selection may affect parents and offspring in different ways and in different directions. This implies that one should carefully examine the costs and benefits of a given maternal effect both in parents and offspring to understand its evolutionary dynamics and adaptiveness. A key problem to consider when tackling the adaptiveness of a maternal effect is to ascertain whether it has truly evolved as an adaptation, or if it is a mere physiological constraint with little room for evolutionary modification. Claims about the adaptiveness of a given maternal effect can be strengthened if it can be shown that parents facultatively vary it as a function of the perceived value of that given reproductive attempt. This prediction arises from life history theory which predicts that parental investment should be correlated with the expected fitness of a reproductive attempt. Here we intend to investigate maternal effects and female egg allocation strategies experimentally using house sparrows Passer domesticus as a model system. We want to address the following questions: 1. Does social competition affect egg composition? 2. Does breeding synchrony affect egg composition? and, 3. Does nest building behavior affect egg quality? ad.1. Specifically we want to know whether females can manipulate the levels of antioxidants, hormones and immune factors in eggs as a consequence of the social environment, and whether there is an optimal level of sociality; ad. 2. There is an ongoing discussion about cost and benefits of breeding synchrony. By experimentally manipulating breeding synchrony we would like to examine in which way it may effect egg quality, and ad 3. If females base their reproductive decisions on male nest building activity, we should expect that eggs laid for males with large nests to be of better quality than eggs laid for males with small nests. To estimate egg quality we will collect one egg from each nest (or extract a small amount of egg yolk) and assess these for content of testosterone, corticosterone, carotenoids, vitamins A and E, and lysozyme.

The study of maternal effects has experienced an extraordinary development in the last decade. Evolutionary biologists no longer consider maternal effects as "troublesome sources of environmental resemblance", but rather as mechanisms that can generate adaptive phenotypic plasticity at the heart of evolutionary responses to natural selection. One important property of maternal effects is that selection may affect parents and offspring in different ways and in different directions. This implies that one should carefully examine the costs and benefits of a given maternal effect both in parents and offspring to understand its evolutionary dynamics and adaptiveness. A key problem to consider when tackling the adaptiveness of a maternal effect is to ascertain whether it has truly evolved as an adaptation, or if it is a mere physiological constraint with little room for evolutionary modification. Claims about the adaptiveness of a given maternal effect can be strengthened if it can be shown that parents facultatively vary it as a function of the perceived value of that given reproductive attempt. This prediction arises from life history theory which predicts that parental investment should be correlated with the expected fitness of a reproductive attempt. Here we intend to investigate maternal effects and female egg allocation strategies experimentally using house sparrows Passer domesticus as a model system. We want to address the following questions: 1. Does social competition affect egg composition? 2. Does breeding synchrony affect egg composition? and, 3. Does nest building behavior affect egg quality? ad.1. Specifically we want to know whether females can manipulate the levels of antioxidants, hormones and immune factors in eggs as a consequence of the social environment, and whether there is an optimal level of sociality; ad. 2. There is an ongoing discussion about cost and benefits of breeding synchrony. By experimentally manipulating breeding synchrony we would like to examine in which way it may effect egg quality, and ad 3. If females base their reproductive decisions on male nest building activity, we should expect that eggs laid for males with large nests to be of better quality than eggs laid for males with small nests. To estimate egg quality we will collect one egg from each nest (or extract a small amount of egg yolk) and assess these for content of testosterone, corticosterone, carotenoids, vitamins A and E, and lysozyme.