Past Winner
2002 NSERC Doctoral Prize

Rees Kassen

Biology

McGill University

It took circumnavigating the globe to prompt Charles Darwin's groundbreaking insights into the origins of the Earth's living diversity. Now, more than 150 years later, Rees Kassen has produced the first experimental proof for why there are so many different species in the world. And he's done it without leaving the lab.

It's leading-edge research for which Dr. Kassen is being awarded a 2002 Natural Sciences and Engineering Research Council Doctoral Prize — one of Canada's premier graduate student awards — as well as the prestigious 2002 Howard Alper Postdoctoral Prize.

Evolution through natural selection poses a conundrum when it comes to the enormous diversity of species on Earth, says the recent McGill University Ph.D. recipient. Natural selection eliminates all but the fittest types from any given environment, thereby, theoretically leading to a reduction in diversity.

So what maintains the wondrous diversity that still exists on Earth? It's a critical question in terms of understanding how to best protect the remaining biodiversity, from wombats to whales.

The scientific challenge has been how to test a process that often requires thousands of years and huge geographic areas.

"Ecology, which involves the study of patterns of diversity across space, has traditionally been about going out into the field and getting your feet wet — muddy boot ecology. But this method isn't very effective for doing experiments because there are too many uncontrollable factors. And large species like birds and trees take too long to reproduce," says Dr. Kassen, now a postdoctoral researcher at Oxford University.

His insight was to eschew the big for the microscopic. The rainforest for the test tube.

The researcher — in conjunction with his thesis supervisor, McGill's Dr. Graham Bell — developed a series of bench-top biodiversity and evolutionary theory experiments using two single-celled microbes, one a bacterium the other an alga. This world-in-a-test-tube approach enabled Dr. Kassen to observe from dozens to hundreds of generations of the clonally reproducing microbes and to completely control their environment.

For one set of experiments Dr. Kassen drew on a classic study first published in 1998 involving the bacterium Pseudomonas fluorescens.

That research demonstrated that if the bacterium were grown in a flask, or environment, that was routinely shaken (and thus homogenized) there was no change in the general diversity of the microbe population. However, if the growth environment was left undisturbed and allowed to segment into distinct micro-environments, there was an adaptive radiation of the population leading to at least three genetically distinct groups.

Dr. Kassen manipulated the amount of energy and the frequency of disturbance in both the homogeneous (shaken) and heterogeneous environments of these bacterium. By doing so he showed that energy and disturbance-related patterns of change are related through a common mechanism: competition in a spatially heterogeneous environment.

"Environmental heterogeneity is key to maintaining diversity," says Dr. Kassen. "My experiments have been able to demonstrate that if you're concerned about maintaining species diversity, you should make sure that you have environments that are qualitatively different from one another."