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Extreme Sunflowers
By Kate Dalke

There are over 50 species of sunflowers, and some have unusual stomping grounds, such as the sand dunes and deserts in Utah and the salt marshes of Texas and New Mexico.

Dune habitat of a hybrid sunflower species, Helianthus anomalus.

Scientists have mapped the genomes of three species of “extreme” sunflowers and discovered that they are wild, healthy hybrids, bred from two different, but closely related, species.

The researchers reported recently that hybridization allowed these species to adapt to new ecological niches; they can thrive in drought or in salty soil. The sudden merging of hundreds or thousands of genes from two species of sunflower in a single generation enabled them to colonize new environments.

The hybrids acquire new, advantageous traits that allow them to inhabit more extreme environments than either of their parents.

This provides some of the clearest evidence to date, the researchers say, that hybridization plays a significant role in evolution. In addition to plants, hybrids occur naturally in birds and fish.

The importance of hybridization in evolution is a hotly debated topic among scientists. It has a clear role in agriculture, where scientists use it to create stronger and more successful crops and livestock.

Yet, some researchers have argued that hybrids are not significant in driving evolutionary change in the natural world. Usually, hybrids are less fit individuals that don’t survive to pass their genes on to the next generation.

The scientists estimate that the sunflower hybrids arose 60,000 to 200,000 years ago from two closely related parental species of sunflower that are widespread in the United States.

“My guess is that [hybridization] happens more frequently than we suspect, but that it is very difficult to detect or prove,” says Loren H. Rieseberg of Indiana University in Bloomington, who led the study and who has studied sunflowers for over 20 years.

The “genetic signature” of a hybrid is probably erased as the organism accumulates genetic mutations over millions of years, he adds.

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Rieseberg, L.H., et al. Major ecological transitions in wild sunflowers facilitated by hybridization. Sciencexpress. Published online August 7, 2003.

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