“Loss of color pigmentation is maintained at high frequency in a monkey flower population”

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Alex D. Twyford, Aaron M. Caola, Pratibha Choudhary, Ramesh Raina, and Jannice Friedman

Loss of anthocyanin pigmentation has risen to an unexpectedly high frequency in a population of Mimulus

The surprising loss of red pigmentation in a plant population

Photographs of representative Mimulus guttatus flowers. That on the left is pigmented, while that on the right is anthocyanin-deficient.
(Credit: Twyford et al., © 2018 The University of Chicago Press)

Almost all land plants make red pigmentation (anthocyanin) in their vegetative tissues or flowers at some point during their lives. It is thought that this pigment protects plants against UV damage, drought, and herbivory, and is also involved in attracting pollinators. A recent discovery finds a population of common monkey flowers (Mimulus guttatus) where a single recessive allele causes complete loss of anthocyanin, and has spread through the population. Alex Twyford and Jannice Friedman first noticed this unique trait in plants grown in the greenhouse, and then returned to the population in Sequoia National Forest to investigate more closely. The team discovered that the genetic variant underlying complete loss of anthocyanin pigmentation has risen to an unexpectedly high frequency in this population. They also found a gene that is likely to be involved, the MYB5 transcription factor, as the unpigmented morphs showed decreased expression in both leaves and floral buds. They then designed 3 sets of experiments to look for fitness differences between the plants that make anthocyanin and those that don’t. They could not find any difference in survival, flowering or seed set, although the unpigmented plants flowered later and grew more clonally. Although they can’t rule out a cryptic selection pressure in the wild, their findings challenge our assumption that the production of anthocyanin is beneficial for plants. The visible color polymorphism also provides an opportunity to examine the dynamics between selection and genetic drift in a well-studied plant species. Read the Article