Species Phylogenies and Macroevolution

Abstract

We proceed now to the provenance traditionally equated with molecular phylogenetics—estimation of evolutionary relationships among species and higher taxa. After reproductive barriers have been erected and the speciation process completed, molecular characters continue to evolve in a more or less time-dependent fashion (Chapter 4), such that the overall genetic distance between species under study provides a compelling guide to the general magnitude of evolutionary time since their common ancestry. Furthermore, many qualitative molecular markers considered individually or in combination can provide powerful characters for clade delineation. In assessing relationships among species, a variety of molecular techniques has been brought to bear, including protein electrophoresis, immunological assays, DNA restriction analysis, DNA-DNA hybridization, and others. In recent years, nucleotide sequencing has become widespread and currently is revolutionizing the field. Collectively, these methods have been applied to phylogenetic estimation in many hundreds of taxonomic groups, at evolutionary depths ranging from closely related congeners to the deepest branches in the tree of life. No attempt will be made here to summarize this vast literature exhaustively. Rather, the purpose of this chapter is to illustrate by chosen examples some of the wide variety of problems and approaches in supraspecific phylogeny tackled through molecular markers.