From millions of wildebeest herd crossing political borders in Serengeti to minuscule bacterial colony moving across agar gel in a petri-plate, migratory behavior can be seen at all scales. Migration has evolved multiple times independently in many animal groups, such as birds, fish, mammals (including marine mammals and bats), and reptiles (e.g. sea turtles) and insects. The tradeoffs between the costs and benefits for the evolution and sustenance of migration have been studied in detail. Although evolution of migration in most cases is a response to seasonal variation in resources, its occurrence and extent depend on many factors such as physical, geographical, historical and ecological which may facilitate and/or constrain the evolution of long-distance migration. Because migration includes a suite of traits, selection of the migratory character will ultimately cause indirect selection on correlated traits and vice versa, and potentially also on traits that have consequences beyond just migration. Testing such interactions require comparison across taxa at large scales. Lack of sufficient data as well as suitable comparative tools have been a major limiting factor to carry out such studies.
For my PhD thesis I plan to investigate the interplay of different selection pressures in defining the course of evolution of migration for passerine birds with more than 5000 species. For this, I have considered two scenarios. In first scenario, I will investigate the evolution of two traits (migration and group foraging) that are likely to facilitate the evolution of each other. In second scenario both the traits (migration and ornamentation) are under different selection pressures and expected to constrain the evolution of each other. To test both these scenarios I am using phylogenetic comparative approaches. In my first chapter, I will test the robustness of three approaches to phylogenetic comparative methods and ancestral state reconstruction to features of our large data sets. I will use simulations where we know the exact evolutionary trajectory and test inferences based on three methods, APE package in R, Mesquite and BayesTraits. In the second chapter I will examine the evolution of group migration in passerine birds and check if group foraging facilitates the evolution of group migration. In the third chapter, I will focus on the interaction of sexual ornamentation with migration and test if the ornamentations which directly impede migration.