Genealogists comb through historical records and family stories to trace a family’s history. But what if you’re trying to piece together a family tree from before humans even existed?
Yaniv Brandvain, a new assistant professor in the Department of Plant Biology, researches the family trees of plants to answer a fundamental question in evolution: why and how do organisms that share a common ancestor split into different species?
“What we’re trying to do is get at the basic question of where species come from, how they split, and if they exchange genes after they split,” Brandvain said.
His organisms of study, including the monkeyflowers, Mimulus, and the Capsella plants in the mustard family, were picked because they each contain species that reproduce differently. Some plant species are “out-crossers,” meaning they reproduce only by mating with a different plant, whereas other plants species are “selfers” and can self-pollinate.
“Most of my work is united by thinking about the species origin of self-pollinating plants,” Brandvain said.
To elucidate species origin, Brandvain sequences the genomes of many different plants within the same species of selfer, and compares them to the genome sequences of several closely related out-crossers. In general, he and other researchers have found that plant species that are selfers evolved from an out-crosser. They can identify bits and pieces of the genome that hybridized, representing parts of the transition between species. He then “does a little bit of math” and is able to build a model of inheritance patterns.
“Some people read the genome as an instruction guide, where you turn this gene on and turn that gene on and you get an organism,” Brandvain says. “What I’m doing is reading the genome as a historical guide where you look at patterns of mutations and patterns of recombination and make a mathematical model and try to understand what happened back in time,” he added.
Selfing vs out-crossing is a convenient distinction to make when performing these genetic analyses, but speciation is, of course, not limited to plants.
“Lots of the methods I work with are related to those methods that we’ve used to tell the story of human history,” Brandvain says. He noted the recent finding of a 45,000-year-old human fossil and how researchers have used that ancient genome to understand how much of the current human line originated from interbreeding with Neanderthals before the two species split. Researchers are also using these methods to understand human migration patterns and to learn when and how populations that had separated came back together and begin interbreeding again.
Brandvain, a native Midwesterner, said he was attracted to the University of Minnesota because it is a world-class university in an “interesting” city with a lot of different things going on. But he’s particularly excited about the many opportunities to collaborate.
“There’s a large group of people with strengths broadly in questions of plant speciation, population genetics and what we can learn about plant evolution,” he said, before rattling off a near-endless list of all the faculty with whom he is excited to work.
— Sarah Perdue