In flowers called columbines, evolution of the length of nectar spurs--the long tubes leading to plants' nectar--happens in a way that allows flowers to match the tongue lengths of the pollinators that drink their nectar, biologists have found.
The researchers were Justen Whittall of the University of California at Davis and Scott Hodges of the University of California at Santa Barbara. They were funded by the National Science Foundation (NSF). Their results appear in this week's issue of the journal Nature.
Darwin once proposed a co-evolutionary "race" to explain how natural selection might account for the evolution of very long nectar spurs in flowers, said Hodges. "In Darwin's race, plants with the longest spurs and pollinators with the longest tongues [to tap the flowers' nectar] would be favored by natural selection, and--in a never-ending process--continually drive the plants' spurs and the pollinator tongues to exceptionally long lengths."
But it turns out, Whittall and Hodges found, that evolution acts in a more one-sided fashion in many plants: the plants evolve nectar spurs to match the tongue-lengths of the pollinators. Then the process stops, and only starts again when there is a change in pollinators.
Whittall and Hodges proved this idea by testing the columbine genus Aquilegia, which is pollinated by bumblebees, hummingbirds and hawkmoths.
They found that most of the columbines' nectar spur length evolution happened during shifts in pollinators from bumblebees to hummingbirds, and from hummingbirds to hawkmoths. In between these shifts, evolution of the columbines' nectar spurs came to a halt.
Whittall and Hodges' work provides evidence that evolution may occur in a stop-and-go pattern--one in which adaptation to specific pollinators occurs very rapidly, followed by periods of no further evolution until another pollinator shift occurs, according to William Zamer, deputy director of NSF's division of integrative organismal systems.
"In the case of these flowers, changes appear to happen relatively rapidly in response to changes in pollinators," said Zamer.
NSF's biocomplexity in the environment emphasis area and division of environmental biology funded the research.
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering, with an annual budget of $5.58 billion. NSF funds reach all 50 states through grants to nearly 1,700 universities and institutions. Each year, NSF receives about 40,000 competitive requests for funding, and makes nearly 10,000 new funding awards. The NSF also awards over $400 million in professional and service contracts yearly.
Receive official NSF news electronically through the e-mail delivery and notification system, MyNSF (formerly the Custom News Service). To subscribe, visit http://www.nsf.gov/mynsf/ and fill in the information under "new users".
Useful NSF Web Sites:
NSF Home Page: http://www.nsf.gov
NSF News: http://www.nsf.gov/news/
For the News Media: http://www.nsf.gov/news/newsroom.jsp
Science and Engineering Statistics: http://www.nsf.gov/statistics/
Awards Searches: http://www.nsf.gov/awardsearch/
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.