CAREER: Phylogenetic scale-dependency of the patterns and processes of quantitative trait evolution

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All life is linked by common ancestry, as revealed by genetic and physical similarities. This is depicted as a tree of life with a single root splitting into many branches, which further split into smaller branches and so on, forming nested groups of species known as clades. To understand the processes that generated the astounding diversity of life on earth, biologists and paleontologists conduct investigations at a variety of scales across this tree, comparing amongst clades of different taxonomic rank (e.g., Genus, Family, Order), size or age. Although rarely acknowledged, it is currently assumed that the conclusions identified at one scale can be applied to all other scales. However, this critical assumption is yet to be validated. This research will investigate how predictable results are across scales, using the highly diverse teleost fishes, which includes approximately half of all vertebrate species. The researchers will determine if patterns of fish body shape evolution are identical, random or vary systematically across scales. Establishing the predictability of these patterns, and processes inferred from them, will determine if and how conclusions drawn at one scale can be applied to another scale. This will have broad implications for synthesizing results across fields that work at different scales and in particular, the ability to connect studies on fossils and living organisms. This project will also improve access to undergraduate research opportunities, integrating students into the scientific discovery process through the development of a Classroom-based Undergraduate Research Experience, and publishing associated Open Educational Resources. This project will build an empirical understanding of how phylogenetic scale influences patterns and processes of quantitative trait evolution. To accomplish this objective the researchers will build upon their existing teleostean body shape dataset of approximately 16,000 specimens from 6,000 species. They will add measurements on a further 17,500 specimens from around 4,500 species to provide denser sampling within species and at shallower nodes in the phylogeny. Two complementary approaches to cross-scale analysis will be used to identify scale-dependency and its predictability. The first will apply mixed Gaussian phylogenetic models of quantitative trait evolution to the full phylogenetic extent to identify parameter shifts; the second will investigate patterns one scale at a time using more traditional phylogenetic comparative methods. Using four ways of delimiting scale: clade age, clade size, tree depth and taxonomic rank, the researchers will also quantify how patterns of scale-dependency are influenced by the method chosen to define scale. Simulations will be used to investigate the potential for statistical artifacts and the influence of methodological and data limitations. These analyses will determine whether phylogenetic scale-dependency is the exception or the rule. The project will also include training opportunities at the undergraduate, graduate student and postdoctoral levels.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.