for National Geographic News
For years scientists have grappled to understand the number and type of genetic mutations required for a new species to evolve. Does it require the accumulation of many minute mutations? Or can a single mutation spark a big change?
Now researchers studying pink and red flowers in the monkeyflower (Mimulus) family have found a persuasive answer: A single mutation can recruit a whole new set of pollinators, serving as the fork in the road that leads to a new species.
"Many mutations are required to get all the way, but the original step can be produced by one mutation," said Toby Bradshaw, an evolutionary biologist at the University of Washington in Seattle.
Bradshaw and his colleague Douglas Schemske, a plant biologist at Michigan State University in East Lansing, mimicked a mutation by switching gene variants that control color from one monkeyflower to another.
Mimulus lewisii are pink and usually pollinated by bees. Mimulus cardinalis are red and usually pollinated by hummingbirds. The birds and bees rarely confuse the flowers, and the flowers almost never interbreed in nature.
The scientists crossed the flowers in a laboratory, breeding red monkeyflower gene variants that control for color into pink monkeyflowers and vice versa.
The results were an orange M. lewisii that drew many hummingbirds and some bees and a dark pink M. cardinalis that drew many bees and some hummingbirds.
"It doesn't switch pollinators as much as it recruits additional pollinators," said Bradshaw.
Writing in a paper published tomorrow in the science journal Nature, Bradshaw concludes with Schemske that "an adaptive shift in pollinator preference may be initiated by a single mutation."
Jerry Coyne, an evolutionary biologist at the University of Chicago, Illinios, said the conclusions of Bradshaw and Schemske "are very sound" and the elegance with which they crossed the species and observed the effect in the field amounts to a "solid and brilliant piece of research."
Crossbreeding
From previous research, Bradshaw and Schemske knew that genes in a certain section of the monkeyflower genome called the yellow upper, or YUP, control the presence or absence of yellow pigments in the petals of M. lewisii and M. cardinalis, and thus whether or not they have their normal pink and red colors.
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