Loren Rieseberg, Professor and Canada Research Chair in Plant Evolutionary Genomics, conducts research on the genus Helianthus in his lab at UBC. Today’s photographs of a hybrid sunflower species, Helianthus anomalus, are from the Little Sahara Sand Dunes in Utah, USA and taken by Jason Rick.
Prof. Loren Rieseberg has tapped the wild sunflower to explore a classic scientific question: How do new species emerge? To find out, his lab at the University of British Columbia marries molecular experiments with classic field studies to learn how radically different hybrid sunflowers arise and colonize new habitats.
Although scientists have long known that wild species hybridize — or mate with plants from different species — most believed that the resulting hybrids were maladjusted, evolutionary dead ends that quickly died out. However, over the past 15 years, Rieseberg has documented the rise of successful wild sunflower hybrids. His lab has compared the genes, physiology, and physical traits of five species: two widespread parental species, Helianthus annuus and Helianthus petiolaris, and three hybrid offspring that evolved between 60,000 and 200,000 years ago. Unlike their parents, the hybrid species — Helianthus anomalus (shown in the photos), Helianthus deserticola, and Helianthus paradoxus — favor extreme habitats: sand dunes, dry desert floor, and salt marshes, respectively.
To capture this evolution in action, Rieseberg’s team replicated it by creating their own hybrids of Helianthus annuus and Helianthus petiolaris in the greenhouse. They analyzed the resulting neospecies for the adaptive traits — such as genes that confer salt tolerance or succulent leaves — needed to colonize the extreme habitats of naturally evolved hybrid species. Working with more than 2000 various synthetic hybrid seedlings, they successfully transplanted them in salt marshes in New Mexico and sand dunes or desert floor in Utah.
The DNA that drives hybrids is markedly different, too, Rieseberg and colleagues have shown. They used quantitative trait locus mapping — a method that taps molecular markers to find genes responsible for phenotypic traits such as leaf shape and seed size — to determine which combinations of alleles a plant has. Among sunflowers, the researchers confirmed that ordinary parent plants from temperate climates can indeed mate and yield hybrid offspring with hardier combinations of the same genes. These new gene combinations, they concluded, allowed the hybrids to colonize new ecological niches, such as salty and dry habitats.
From Brown, K. 2003. No garden-variety biologist. Science 302:1499. This entry is third in a series for UBC Research Week.