Instant Evolution in Whiteflies: Just Add Bacteria
ScienceDaily (Apr. 8, 2011) — In just six years, bacteria in the genus Rickettsia spread through a population of the sweet potato whitefly (Bemisia tabaci), an invasive pest of global importance. Infected insects lay more eggs, develop faster and are more likely to survive to adulthood compared to their uninfected peers.
Sweet potato whiteflies are often seen in pairs, like these two on a plant leaf. UA researchers discovered that Rickettsia bacteria give the tiny pests an evolutionary edge over their non-infected peers. (Credit: Stephen Ausmus)
The discoveries were made by a University of Arizona-led team of scientists and are published in the April 8 issue of the journal Science.
"It's instant evolution," said Molly Hunter, a professor of entomology in the UA's College of Agriculture and Life Sciences and the study's principal investigator. "Our lab studies suggest that these bacteria can transform an insect population over a very short time."
It is not uncommon to find a microbe providing some benefits to their hosts, but the magnitude of fitness benefits we found is unusual," she added.
In addition to the observed evolutionary advantages -- which biologists call fitness benefits -- Hunter's team discovered that the bacteria manipulate the sex ratio of the whiteflies' offspring by causing more females to be born than males.
According to Hunter, the bacteria are transmitted only through the maternal lineage (from mother to offspring). Therefore, it is beneficial for them to make sure more female than male whiteflies are born.
"However, we don't know how they're doing that yet," she said....
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Science 8 April 2011: Vol. 332 no. 6026 pp. 254-256 DOI: 10.1126/science.1199410REPORT
Rapid Spread of a Bacterial Symbiont in an Invasive Whitefly Is Driven by Fitness Benefits and Female Bias
Anna G. Himler1,2, Tetsuya Adachi-Hagimori2,4, Jacqueline E. Bergen2, Amaranta Kozuch2, Suzanne E. Kelly2, Bruce E. Tabashnik2, Elad Chiel2,3, Victoria E. Duckworth2, Timothy J. Dennehy2,5, Einat Zchori-Fein3, and Martha S. Hunter2,*
Author Affiliations
1Center for Insect Science, The University of Arizona, Post Office Box 210106, Tucson, AZ 85721–0106, USA.2Department of Entomology, The University of Arizona, Forbes 410, Tucson, AZ 85721–0036, USA.3Entomology Lab, Newe Ya’ar Research Center, Agricultural Research Organization, Post Office Box 1021, Ramat Yishay, 30095, Israel.4Research Institute of Environment, Agriculture and Fisheries, Osaka Prefectural Government, 442 Shakudo, Habikino, Osaka 583-0862, Japan.5Global Insecticide Resistance Management, Bayer CropScience Limited Partnership, 2 T.W. Alexander Drive, Research Triangle Park, NC 27709, USA.*To whom correspondence should be addressed. E-mail: mhunter@ag.arizona.edu
ABSTRACT
Maternally inherited bacterial symbionts of arthropods are common, yet symbiont invasions of host populations have rarely been observed. Here, we show that Rickettsia sp. nr. bellii swept into a population of an invasive agricultural pest, the sweet potato whitefly, Bemisia tabaci, in just 6 years. Compared with uninfected whiteflies, Rickettsia-infected whiteflies produced more offspring, had higher survival to adulthood, developed faster, and produced a higher proportion of daughters. The symbiont thus functions as both mutualist and reproductive manipulator. The observed increased performance and sex-ratio bias of infected whiteflies are sufficient to explain the spread of Rickettsia across the southwestern United States. Symbiont invasions such as this represent a sudden evolutionary shift for the host, with potentially large impacts on its ecology and invasiveness.
Received for publication 22 October 2010.Accepted for publication 10 February 2011.
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