Evolution and Flower Color

Here’s an interesting twist that I’ve never seen before.

Study of flower color shows evolution in action

29.jun.09

Gail Gallessich

University of California - Santa Barbara

Santa Barbara, Calif. – Scientists at UC Santa Barbara have zeroed in on the genes responsible for changing flower color, an area of research that began with Gregor Mendel’s studies of the garden pea in the 1850’s.

In an article published recently in the Proceedings of the National Academies of Sciences, two researchers document their studies of the evolution of columbine flowers in North America. They studied red columbines pollinated by hummingbirds, and white or yellow columbines pollinated by hawkmoths. They believe that a color shift from red to white or yellow has happened five times in North America.

“What is important in this research is that hawkmoths mostly visit – and pollinate – white or pale flowers,” said senior author Scott A. Hodges, professor of ecology, evolution and marine biology at UCSB. “We have shown experimentally that hawkmoths prefer these paler colors.”

When a plant population shifts from being predominantly hummingbird-pollinated where flowers are red, to hawkmoth-pollinated, natural selection works to change the flower color to white or yellow, he explained.

“Ultimately we want to know if evolution can be predictable,” said Hodges. “In other words, we want to know if each time there is an evolutionary change in flower color, does it happen in the same way? Having identified all the genes that are intimately involved with making red and blue columbines now allows us to determine how these evolutionary transitions have occurred.”

In earlier research, Hodges showed that flowers evolve in a predictable fashion to match the mouthparts of pollinating birds and insects. Thus the pollinators of the yellow columbine flower, A. longissima, are predicted to have exceptionally long tongues to reach the nectar at the bottom.

Graduate student Nathan J. Derieg is the second author. This research was entirely funded by the National Science Foundation. It is part of a large multi-university study funded by the NSF through UCSB.

Very interesting article! Thanks for the post! Brings me back to a question I ponder from time to time: why are wild roses (predominantly) pink?

“What is important in this research is that hawkmoths mostly visit – and pollinate – white or pale flowers,” said senior author Scott A. Hodges, professor of ecology, evolution and marine biology at UCSB. “We have shown experimentally that hawkmoths prefer these paler colors.”

That hawkmoths are collecting nectar at night is the key. Most (all?) night crosspollinated flowers are white, larger and often more scented than the day pollinated ones as it is a necessity for pollinators to find them in the dark.

In the same genus i.e. big columnar cactis the bat night pollinated Trichocereus have very large white heavily scented flowers when the day pollinated relatives have tinier often red and not scented flowers that most hummingbirds pollinated flowers have.

It is coevolution. Or selection by pollinator.

Just what we are doing :wink:

I agree, Pierre. Roses aren’t dependent on nocturnal pollinators, as we can deduce from the fact that many single roses close at night. Therefore the light coloring favored by moths would not provide an adaptive advantage to roses.

Pink, on the other hand, is visible from a great distance, at least to this mammalian eye. I recently discovered an intense pink rose seedling at least 150 yards from the nearest rose, nestled in the ground among the sprouting roots where I’d removed a massive Baccharis pilularis in the middle of 15 acres of grasslands. The two inch tall rose stood out like a beacon.

I wonder if roses are truly dependent on pollinators. Does anyone know the source of the conventional wisdom that most OP seedlings are selfs? Or if the petals are removed, whether most roses would still be pollinated?

For sure some roses are obligatorily outcrossing (self-incompatible). Others seem to almost never take foreign pollen. I think some Japanese workers said it was diploid vs tetra that made the diff.

It’s true that pink is visible from some way off, but only in insects, birds, old-world primates and a very few new-world primates. The mammalian gene for seeing red (as it were) is a fairly new mutation of the gene for seeing green.

So, that being the case, I would say that yes, the pink color is to attract pollinators. But why, I wonder, would pink work better than, say, yellow…

and suddenly, it occurs to me… maybe roses are pink because most mammals, and certainly no native temperate climate mammals, can see the color and come eat the flowers. (Though my horses will eat rose flowers that grow along the fenceline. I think they find them by scent. Or in Candy’s case, they have carbon atoms in them ergo they are food…)

I wonder then, if the pink color may be the plant’s way of saying, “Flying Pollinators Only Need Apply.”

As far as roses being dependent on pollinators, there’s an easy way to find out. I’ve got a stand of R. arkansana just coming into bloom now. It would be interesting to see what happens if I pull off all the petals…

Which reminds me to mention (sorry for blathering so this morning), the bees out here will indeed visit the flowers you’ve pulled all the pollen off of. Oh well.