Early life is a critical stage during which the environment experienced can have important life-long effects for an individual. Understanding how the interaction between an individual's genes and the environment during early development create the variation seen in nature is an important question in Biology. This research will leverage a well-established study system for evolutionary and behavioral research to determine how the developmental environment shapes the expression of a trait that is critical to reproductive success later in life. Specifically, this study will manipulate nest parasites, an important component of the environment, during early development to determine how parasite infections and the immune responses they generate interact with the genes that underlie plumage color in birds. Plumage color, here a brownish-red melanin coloration, is an important signal used in communication between the sexes and it is impacted by early life conditions, and therefore the reproductive success of an individual. Genes expressed in tissues where feathers are grown will be measured to allow for the identification of specific genes whose expression is influenced by environmental conditions. Results from this work will be broadly informative as melanin is a common pigment underlying appearance and coloration in various groups of animals. However, it is not well understood how the environment interacts with genes to influence the development of melanin coloration. Broader impacts include training undergraduates and middle-school teachers in scientific research, and the creation of lesson plans that will be implemented in public middle schools and shared broadly with teachers at science-teaching workshops.
Female preferences for male coloration are thought to be adaptive because of the potential information advertised by these male traits. Melanin-based color traits are traditionally thought to be under strict genetic control. However, condition-dependence for some melanin traits may occur during early development. If so, trait variation may provide information about an individual's developmental history. Previous work has shown that variation in melanin-based color in barn swallows is due almost entirely (70%) to differences in early environment, and that plumage color provides information about ectoparasite loads in a male's territory. Mites affect nestling survival, growth, immunity, and melanin-based plumage color. This project will identify gene expression differences associated with color variation by cross-fostering eggs and manipulating mites to tease apart the roles of genes and environmental quality. Developing feathers will be collected and RNA expression will be quantified to understand how early environment interacts with genes in the melanin pathway to influence the life-long expression of a melanin-based signal. The research will have important implications for understanding the gene by environment interactions during the early developmental period for melanin-based ornamental traits, and thus, information that females gain by using these traits. Results from this work will provide a clearer picture of how melanin-based traits interact with the environment during development at many levels: from the detailed gene expression, to lifelong trait expression, to variation within a population and how this relates to the parasite community, and finally to divergent morphological traits across populations that are involved in reproductive isolation.
