This project is an extension of previous findings that strongly suggest that adaptive evolution of flower color in a species of morning glory, Ipomoea quamoclit, is accompanied by degeneration of part of the anthocyanin pigment pathway. The primary objectives of this project are (1) to determine definitively whether such pathway degeneration has occurred in I. quamoclit, and (2) to determine how general an evolutionary phenomenon such degeneration is. Pathway degeneration will be assessed by using in vitro enzyme assays and in vivo complementation assays to determine whether individual genes in the pathway retain their ancestral function. Phylogenetic analyses and ancestral state reconstruction will be used to determine whether some loss-of-function substitutions occurred after the adaptive transition shift in pigmentation, as would be expected if those substitutions reflect pathway degeneration. In addition to examining I. quamoclit and closely related red-flowered species in more detail, we will also assess whether anthocyanin pigment pathway degeneration has occurred in white-flowered morning glories in the Calonyction group, and in the model species Arabidopsis thaliana, in which only blue and not red anthocyanins are produced.
A general principle in evolutionary biology is that evolutionary loss of characters is often permanent. While many investigations have documented this pattern, little is known about why character loss is irreversible. The general scientific importance of this research is that it seeks to evaluate, and provide mechanistic justification for or against, the hypothesis that irreversibility results from the evolutionary breakdown of complex characters that are not currently used.
