Inferring Ancestral Character States
We wish to address the question of how much information is available in a set of observable individuals to help us reconstruct the ancestral state of a character. The question can be framed in variety of contexts, but we focus on the following scenario. An investigator is studying a group of organisms that are related by a phylogenetic tree with a known topology and known branch lengths (presumably based on a sufficient amount of prior data). A new character is observed, and the investigator wishes to infer the state of the character at one or more of the internal nodes of the tree. This scenario was motivated by a study of fungus-growing ants for which a molecular phylogeny of the ant species is available (Fig. 1) and the character of interest is the type of fungus grown (T. Schultz, personal communication).
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