Phylogenetic Analysis of Murid Skull Shape Ontogeny

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Many features of an animal, such as its skull shape, change throughout its life. Yet, comparative studies of skull shape, including those that seek to infer evolutionary relationships among groups, and those that examine evolutionary changes in skull form, commonly survey only adults. The proposed research will analyze developmental changes in skull form to determine whether these transformations provide information about evolutionary relationships among selected rodents, and to dissect evolutionary changes in skull development. Recent advances in methods for quantifying shape change have yielded promising techniques that will be applied in this analysis. The method of thin-plate splines, the method that I propose to use, has a unique advantage in that it gives a way to identify a series of independent shape characters that have specific location and spatial extent on the skull. In the first stage of this project, I will compare three genera of murid rodent Mus, Sigmodon and Peromyscus. Relationships among these genera are not controversial. I will compare: 1) transformations in skull shape from age to age in each species; 2) average skull shape at each age across species; and 3) intraspecific variability of skull shapes and their transformations. This phase of the research will explore several methodological issues, such as methods for coding developmental transformations of shape characters. The second stage of the research will use these methods to analyze relationships among Sigmodon species, and to describe evolutionary modifications of skull growth.