Phylogeny of Sleep
Collaborators on these studies are Drs. Charles Nunn (Max Planck Institute, Leipzig, Germany and Harvard University, Dept. of Anthropology) and Robert Barton (University of Durham, Durham, UK).
This research was funded by NIMH Grant number: 1 R01 MH070415-01A1.
Project Title: Phylogeny of Sleep
A large proportion of the variance in comparative biological variables is commonly associated with two factors: body size and phylogeny. Allometry is the study of how a trait scales with body size. Most, if not all, biological variables show a phylogenetic signal even after removal of the effects of body size. That is, the degree of similarity between organisms is partly a function of their phylogenetic propinquity. Indeed, in order to properly describe the scaling of a trait, it is necessary to take phylogenetic effects into account. Hence, analysis of scaling and of phylogenetic effects must go hand-in-hand. We generally ask three types of phylogenetic questions that are relevant to untangling potential evolutionary functions of a given neurobehavioral system: First, do phylogenetically close species share similar trait values with respect to the system in question? This assumption underlies most phylogenetic analyses of character evolution but is rarely tested. Second, which system-related traits are evolutionarily primitive for mammals vs. birds or reptiles, which are derived, and which similarities have arisen by convergent evolution? Documentation of broad taxonomic differences, such as those proposed between mammalian orders, will guide subsequent testing of hypotheses about the evolutionary correlates of the system’s traits. Third, do groups of taxa exhibit different scaling relationships? A deeper understanding of allometric patterns can be accomplished through understanding such “grade shifts”. Furthermore, major phylogenetic effects are themselves of interest to investigate whether particular taxa evolved distinctively different patterns of with respect to the system’s trait values, and if so, how these patterns relate to other features of their biology such as reproductive functions, diet, and other life-history characteristics.