High-speed Evolution

Rapidly reproducing organisms can noticeably evolve over a span of mere hours

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Evolution teaches us that every living thing adapts to its environment, over many generations, and leading in many different directions. As a result, diversity surrounds us. We have tiny single-celled organisms like bacteria and yeast that reproduce constantly, but we also have larger organisms that reproduce over hundreds of years.

Typically when we think of studying evolution, we think of studying the fossil record. However, modern evolutionary biologists like Sally Otto, professor in the Department of Zoology at the University of British Columbia, are looking to observe evolution as it happens. By choosing organisms that reproduce rapidly, such as yeast, evolutionary processes can happen within hours.

Studying these processes is possible because we now have the technology needed to sequence DNA, the blueprints that hold the instructions for how different living things are built. When cells divide, they have to make a copy of their DNA so that there is a copy for each new cell. From time to time there are errors in the copies, and these are called mutations. Sometimes mutations result in new traits that are well suited for a particular environment. In the lab, Otto can apply different incentives for adaptation, such as exposure to toxic substances, and then look for genetic mutations and track how new traits and adaptations spread to better understand how organisms evolve.

Capturing these responses is critical to our understanding of the living world. Otto explains that “evolution impacts every aspect of our lives: from the viruses inside us, to the foods that we eat, to the forest and fish around us. Everything is evolving all the time… If we want to design better drugs, if we want to plant trees in places that make sense for those trees, we’d better understand how genetically diverse they are and how selection is acting on those populations; otherwise we make unwise decisions. And that’s in medicine, in agriculture, in forestries and fisheries.”

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Prof. Sally Otto is a theoretical biologist whose research focuses on fundamental questions of population genetics and evolution, such as why some species reproduce sexually and why some species carry more than one copy of each gene. Diploidy (having two gene copies) was long thought to represent a mechanism for masking the effects of deleterious gene mutations; a second, “good” copy of the gene can still perform the necessary function, but carrying two copies of each gene also makes it easier for deleterious mutations to persist in a population. In a series of studies, Prof. Otto and colleagues have analyzed the balance of these evolutionary forces, predicting that multiple gene copies are favored in species with extensive sexual reproduction, where genes are continually placed in new combinations and the “bad” copies are masked; by contrast, fewer gene copies are favored in less sexual species, where the benefits of ridding a lineage of its bad mutations matters more. The details and specificity of Prof. Otto’s models resolve long-standing conceptual questions regarding the evolutionary benefits of sexual reproduction and allow for empirical investigation of a wide variety of related phenomena, such as the ecological structure and conditions that favor sexual over asexual reproduction, the ratio of males and females in a species, the duration of haploid and diploid phases in species’ life cycles, and the role of sexual reproduction in host-parasite coevolution. In addition to participating actively in laboratory and field experiments to test and refine her models, Otto is a dedicated educator, having recently co-authored an acclaimed textbook on mathematical modeling that introduces other biologists to the power and rigor of quantitative analysis. Prof. Otto’s extensive track record of bringing fresh perspectives to thorny conceptual problems suggests that her fundamental contributions to ecology and evolution will continue unabated.

Prof. Otto received a B.Sc. (1988) and a Ph.D. (1992) from Stanford University. She joined the faculty at the University of British Columbia in 1995 as an assistant professor of zoology and is currently a professor in the Department of Zoology and director of the Biodiversity Research Centre. She is the co-author of A Biologist’s Guide to Mathematical Modeling in Ecology and Evolution (2007), and her scientific articles have appeared in such journals as Science, Nature, PNAS, and Evolution.