wednesday, february 15, 2012 3
The california aggie
Evolutionary “founder effect” detected Scientists conducted experiment on small Caribbean islands
By BRIAN RILEY Aggie Science Writer
Thomas Schoener and David Spiller, both professors in the UC Davis Evolution and Ecology Department, are among the co-authors of a new study appearing in Science magazine that provides evidence for an evolutionary phenomenon called the “founder effect.” The founder effect is the evolutionary theory that a small number of “founders,” or initial members of a population in a specific location, can have a longlasting effect on the genetic composition of subsequent generations. “We actually saw a hurricane [in 2004] wipe out a population of lizards on small islands that we had been monitoring,” Schoener said. Since the cays, or tiny islands, were cleared of lizards, they were able to introduce male and female lizard pairs on a number of island cays as an experiment to test the possible effects of the founder effect. “Most of the vegetation [after a hurricane] survives,” Schoener said. “The other things come back fairly quickly. Spiders get completely extirpated, but most of the arthropods can come back pretty quickly. Either they fly, or with the case of the spiders they balloon.” Schoener, as part of a previous study, had in-
Manuel Leal / Duke University
The brown anole lizard helped study the controversial phenomenon called the “founder effect.” troduced larger founding populations to small islands, with a ratio of three females to two males. For the current study, however, the researchers decided to test the smallest possible number of lizards which could potentially form a founding colony: one female and one male. “That’s as small as you can get,” Schoener said . They chose seven pairs of lizards from forests containing large trees on a large island to be introduced on seven small cays where there were small bushes. Scientists monitored the lizards to see if the lengths of the lizards’ hind legs became shorter over subsequent generations. They measured the leg lengths of the male
and female founders on a particular cay to see if the founder leg lengths had a lasting effect on subsequent generations or whether processes such as natural selection or genetic drift were enough to explain the lizards’ evolving leg lengths. Schoener found that both natural selection and founder effects were involved in the leg lengths. They were able to find lasting influences of the initial leg lengths on subsequent generations. “Adaptive evolution,” said David Reznick, a biology professor at UC Riverside who was not involved in the study, is “genetic change in populations that makes them better able to survive and produce offspring in a given environment.”
For example, lizards living among small bushes would be expected to develop smaller hind legs after successive generations to facilitate walking on the small branches. It was not known whether “just one male and one female harbor sufficient genetic variation for adaptive evolution to be possible,” Reznick said . “Their experiment suggests that’s true and that was not expected.” “I think the uniqueness of this study derives from its focus on an evolutionary process that doesn’t get much attention. Natural selection certainly dominates the study of evolution and the public’s perception of it,” said Michael Kinnison, a biology professor at the University of Maine who was not involved in the study. “However, in reality, natural selection is one process among several that are thought to shape genetic diversity.” “What their study shows is that there was in fact a founder effect,” Reznick said. “There’s a real trace of adaptive evolution there and it happened very fast, in spite of the very small number of founders.” For the current study, Schoener said, “We kind of took a chance, and it paid off.” BRIAN RILEY can be reached at science@ theaggie.org.
UC Davis strikes back against food poisoning $25 million USDA project seeks to eradicate E. coli from food production By HUDSON LOFCHIE Aggie Science Writer
Over the past 60 years, E. coli has been the primary model organism for gene sequencing and recombinant DNA experiments. While the majority of these E. coli strains are harmless, there exist a few strains that, when present in the human body, cause severe food poisoning and intestinal havoc. UC Davis is a member of a largescale research project funded by the United States Department of Agriculture (USDA) geared toward reducing amounts of the E. coli pathogen in cattle and processing plants. They also seek to educate both restaurants and individual consumers in safe storage and preparation methods. According to the USDA grant proposal, there are 9.4 million cases of food-borne illness every year, with an estimated social cost of $1.4 trillion in sick days and loss of productivity. One of the primary culprits behind these extreme cases is the E. coli strain 0157:H7, but other harmful strains include the 0104 strain. “Over 50 people were killed in Germany [in 2011] by the 0104 strain,” said Terry Lehenbauer, the associate director of the UC Davis Veterinary Medicine Teaching and Research Center (VMTRC). The strains the researchers are looking to minimize are in the groups Shigella and enterohemorrhagic E. coli (EHEC). The Shigella strains produce toxins, known as Shiga toxins, which are responsible for dysentery, colitis and renal failure. The EHEC, of which 0157:H7 and 0104 are members, produce other toxins called verotoxins that cause bloody stools, and infection and inflammation of the large intestine. E. coli can infect anyone, but the highest at-risk groups are the elderly, young children and people with diabetes. The portion of this project based in Davis is focused on eliminating
well. They die without descendants to pass on those unappealing genes. Similarly, a bee doesn’t look at a flower and think, “I’ll help that flower spread Amy its pollen to another flowStewart er. I’m just a good bee like that.” All the bee wants is the sweet nectar that the flower makes (another evolutionary attractant for the pollinators). In the process of satisfying its own love for nectar, the fuzzy bee ends up covered in pollen that it then takes to the next flower; fertilization is a happy lowers are the iconic Valentine’s Day gift. accident. Explaining these evoluIf a person gets nothing else for their significant tionary concepts can be difficult without humanizother, especially since coling the players. It feels natlege students are usually on a budget prohibiting ex- ural for us to say, “The flowpensive dinner reservations er wants to attract the pollior shiny jewelry, the couple nator,” even though plants will probably still exchange obviously don’t have a brain to want anything, at least in flowers. the same way humans want I’d like to encourage something. you to look closer at those It seems natural beflowers. Since this is being published the day after cause, on some level, we know that Valentine’s every living Day, they might still ... the basic idea is the same: thing has the be on your find a way to pass on your same need — to survive table or genes to the next generation and reprodesk. If duce. These you took a needs do get basic biology class, you already know complicated when talkthat a flower is the main re- ing about what humans actually want; not everyone productive part of certain plants; specifically, a group wants children, after all. However, where do we of plants called angiodraw the line? At what sperms. In a certain sense, a flow- point between, “The flower needs to reproduce,” and er’s purpose is indeed to “The flower tries to trick a look “pretty.” However, pollinator to come near,” this isn’t for the good of does it become overly huthe people who pick them manizing? This line is actuto give to their lovers; this ally rather difficult to disis for their own good. The more attractive the flower is tinguish. It seems obvious that to its respective pollinator, whether bees, birds or bats, the verb “trick,” for examthe more likely it is to fertil- ple, implies a rationality and purpose that a simple plant ize and spread its seed. This is just a basic evolu- does not have. The problem tionary concept. The differ- is that it’s hard to think of another word that describes ences between plants with what the Ophrys exaltata, flowers and people when an orchid species, does to it comes to reproduction are fairly obvious; since hu- bees: it looks like a female bee and even exudes somemans can move to their what similar smells, so simisexual partners, a different lar that male bees have been species acting as a vector known to attempt to mate isn’t required. with and then ejaculate on However, the basic idea the flower. is the same: find a way to It goes beyond that, pass on your genes to the though. The smell they make next generation. The only is actually slightly different difference is the strategy. Angiosperms split from than the females in the bee population, making it odd their non-flowering cousthat they are trying to imitate ins, gymnosperms, about the bees. However, what sci200 million years ago. entists have found is that the While gymnosperms usually use methods like wind bees are actually much more likely to visit orchids that travel to disperse their seeds, flowering plants use smell slightly different from their own population than other methods. those that smell the same. Even a glance at different types of flowers shows a The orchid is not trying large diversity of shape. The to be dishonest; it’s just that the orchid flowers that hapreason for this is the pollinators. Flowers co-evolved pened to look like the female bee were more likely to surwith their pollinators over vive. There was no intent to millions of years, adapting deceive. That’s just the way it shape and color to be the happened. most attractive to their re I wouldn’t recommend tryspective helper. ing to use that as an excuse Not that there are intentions behind these adapta- with your significant other, though. tions. Flowers with genes that make them look unappealing to the pollinators AMY STEWART can be reached at in the area don’t reproduce firstname.lastname@example.org.
Eric Erbe / USDA
E. coli infected beef can cause food poisoning, nausea. the presence of these bacteria on animal hides and looking for ecologically sound methods of making food processing safer. Researchers are using specific electrical currents that are harmless to the animals but inactivate E. coli cells. The research will also focus on learning more about these endemic pathogens. “Know your enemy,” said James Cullor, director of the VMTRC. “We are working on diagnostic methodologies so we can find these things, track them and find out their biology.” Davis’ role in the project also delves into the consumer side of prevention. Davis will be developing intervention strategies and training programs to teach proper handling and preparation of potentially contaminated food products. “We videotaped a group of people preparing hamburgers and salads and saw that less than half of them used soap when washing their hands,” said Christine Bruhn, director of the Center for Consumer Research at UC Davis.
Bruhn’s research has shown that the majority of infections are due to poor sanitation in the home and kitchen, so she will be part of an effort to work with hospitals and health care providers to teach people about proper preparation and sanitation. These programs will work to teach new generations proper food preparation methods that were common knowledge to previous generations. “Less than 2 percent [of people] feed the other 98 percent. Each generation is getting farther and farther away from the basic knowledge of food safety,” Cullor said. The USDA project is a five year, $25 million endeavor with specific goals set up along the way. Aside from UC Davis, the other involved institutions include University of Delaware, New Mexico State University, Texas A&M, Virginia Tech, the University of Arkansas and the USDA Agricultural Research Service. HUDSON LOFCHIE can be reached at science@theaggie. org.
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