Yellow Evolution: Unique Genes Led to New Species of Monkeyflower; Pigment Permutations Suggest New Genes Are What Make a New Species

Plants of the genus Mimulus (Monkeyflowers) have a great diversity of flower color and shape. (Credit:Yuan Mimulus Lab, Pete Morenus/UConn).

Monkeyflowers glow in a rich assortment of colors, from yellow to pink to deep red-orange. But about 5 million years ago, some of them lost their yellow. In the February 10, 2023 issue of Science, University of Connecticut (UConn) botanists explain what happened genetically to jettison the yellow pigment, and the implications for the evolution of species. The Science article is titled “Taxon-Specific, Phased siRNAs Underlie a Speciation Locus in Monkeyflowers.” Monkeyflowers are famous for growing in harsh, mineral-rich soils where other plants can’t. They are also famously diverse in shape and color. And monkeyflowers provide a textbook example of how a single-gene change can make a new species. In this case, a monkeyflower species lost the yellow pigments in the petals but gained pink about 5 million years ago, attracting bees for pollination. Later, a descendent species accumulated mutations in a gene called YUP that recovered the yellow pigments and led to production of red flowers. The species stopped attracting bees. Instead, hummingbirds pollinated it, isolating the red flowers genetically and creating a new species. UConn botanist Yaowu Yuan, PhD, and postdoctoral researcher Mei Liang, PhD, (currently a professor at South China Agricultural University), with collaborators from four other institutes, have now shown exactly which gene it is that changed to prevent monkeyflowers from making yellow. Their research adds weight to a theory that new genes create phenotypic diversity and even new species.

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