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Past Winner
2007 E.W.R. Steacie Memorial Fellowship

Andrew J. Roger

Biochemistry and Molecular Biology

Dalhousie University


Andrew J. Roger
Andrew J. Roger

Andrew Roger is putting together a family tree, but not the kind most people are used to. For starters, it's far, far bigger than any genealogy most of us are familiar with. Not to mention that it contains a lot of distant cousins that most of us didn't know about.

Dr. Roger is a molecular biologist at Dalhousie University, and the family tree he is helping assemble comprises all eukaryotic organisms – those whose cells contain their genetic information in the form of chromosomes in a nucleus. Along the way, he has uncovered dramatic evidence about the timing and nature of two billion years of evolutionary events in the development of eukaryotes, work that has earned him a 2007 NSERC E.W.R. Steacie Memorial Fellowship.

In contrast with historical methods of identifying and classifying species that focused on observing their physical characteristics, today's method of choice involves a combination of molecular biology and genetic analysis. Not only does this allow for more precise comparisons between different organisms, but it also offers clues about possible common ancestors. The more genetic information two organisms have in common, the more likely it is that they have a relatively recent (in evolutionary terms) ancestor.

While anatomical clues do a reasonable job of classifying the traditional animal kingdoms, they aren't of much use with microscopic organisms. “Beyond those kingdoms it wasn't at all clear what was going on because it is difficult to recognize anything that would indicate which kingdoms are more closely related to others,” says Dr. Roger. “The only way that was possible was through genome sequencing. So now we can look at their genes and look further back into the past.”

This field has progressed in leaps and bounds in the past 15 years, with Dr. Roger making a substantial contribution.

Assembling the pieces of this genetic puzzle involves intensive data collection and sophisticated computational techniques, with Dr. Roger playing an important role in developing new tools and statistical models. His analysis has led to the hypothesis that there are in fact six “super-kingdoms” of eukaryotic organisms, a model that is gaining acceptance. As an illustration of how vast a sampling of organisms is under discussion, humans and all animals form only part of one of these super-kingdoms.

Historically, more attention has been focused on larger organisms, but Dr. Roger feels that studying the apparently more primitive one-celled organisms will shed light on some of the earliest evolutionary events.

“It's still pretty controversial,” he admits, in reference to his super-kingdoms theory. The ability to distinguish most species via their genetic makeup has been available for only a short time, so it's not surprising that his ideas are subject to intense scrutiny on the part of the international biology community. The most intense debate swirls around the right way to group the countless examples of tiny one-celled and multi-celled organisms, which turn out to have a startling amount of genetic diversity as well as an uncanny ability to evolve quickly.

Researchers also differ on the best way to estimate how long ago various evolutionary events took place. Several methods have been proposed, but collecting a lot more data is really the only thing that will resolve the debate.

Dr. Roger's approach to data collection revolves around “expressed sequence tag surveys.” Rather than cataloguing all of an organism's genetic information, an exhaustive task for such a large number of organisms, he is sampling only the genes that are expressed, or “turned on.” During the course of his NSERC Steacie Fellowship, he hopes to use this method to continue filling in branches of the tree of life that Charles Darwin envisioned some 150 years ago. Actually it's more like an interconnected web – Dr. Roger believes all life is traceable back to one organism, but that there are also lateral connections between branches as a result of genetic information being transferred from one organism to another.

That lateral gene transfer and the resulting ease with which one-celled organisms can change their genetic makeup is one of the surprising revelations generated by Dr. Roger and his group. “We have found that a lot of these single-celled organisms are getting genes from the environment they live in or from their food organisms,” he explains. “They're not just inheriting genes from an evolutionary tree but they're acquiring them. Organisms can diversify by this mechanism much faster than we thought.”

Another of Dr. Roger's discoveries involved finding genetic evidence that evolution does not necessarily always move towards making an organism more complex. “Organisms can become simple because they do away with things they don't need,” he points out. For example, the parasite Giardia and its relatives were originally thought to be more primitive because they do not contain mitochondria (an “organelle” that acts as a sort of power supply for cells), but he has found genetic markers indicating that they in fact contained mitochondria in the past and evolved away from them to adapt to life in an oxygen-free environment.

In addition to satisfying our long-standing curiosity about how life evolved, this research has potential implications for medicine and agriculture, among others. For example, understanding the process by which bacteria acquire genes from their environment may help predict how quickly new strains will develop, in addition to providing clues about dealing with new pathogens. Finding out which genes are unique to certain harmful organisms can also be helpful, since a therapy could offer a risk-free treatment by targeting only that gene.

The task of constructing the tree of life is a long-term commitment, but Dr. Roger expects each new organism that comes his way to provide a missing link in his statistical models that will ultimately provide a clear picture of how life on earth evolved.