THE OAK TREE GENETICIST

Paul Gugger uses genes to predict the fate of oak trees in the face of climate change.

By Amelia Taylor-Hochberg

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Quercus robur. Drawing by Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany.

Quercus robur. Drawing by Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany.

In 2004, the United States Congress passed legislation designating the oak as America’s National Tree. Joining the ranks alongside the bald eagle and the rose, the oak was a natural and popular choice: there are about 90 oak species total, spread across nearly every state, and voters had already selected Oaks in the Arbor Day Foundation’s poll for America’s National Tree. How democratic.

Why Americans preferred oaks to pines, elms, firs or maples is impossible to say. But looking at the oak’s basic form, there’s an automatic, reassuring familiarity to it, in the same way that a good pop song makes you feel like you’ve known it all your life after listening to it only once. The Oak's giant mop-top of tangled leaves, balanced on a squat trunk with thick gnarly branches, begging to be climbed, is what schoolchildren conjure with markers as the prototypical “tree”.

The designation oak refers to the genus, Quercus, member of the beech family, Fagaceae. Native to North America, oaks are flora heavyweights in the American landscape: they account for more biomass in North America than any other tree genus, and many species are integral “keystone” or “foundational” members of their local ecologies, meaning that they are relied upon by many other species for a variety of uses: habitat, food, tools, etc.

The standby personifications we tend to tack onto oaks – their old age makes them wise, their wide trunks confer stability and reliability, their plentiful shade offers hospitality – align with their biological realities. Foundational species in ecological terms become the footing for our colloquial speech, for our poetry. The oldest living oak, the Pechanga Great Oak in Temecula, California, is 2,000 years old. It’s nearly impossible not to feel humbled and deferential in the shadow of something that’s the same age as Christ.

Coast live oaks are found almost exclusively on the Californian and northern Mexican coast. On the other side of the U.S., oaks extend from Florida to southern Canada, but some species are pickier than others, and exist in more restricted area– some in response to the stresses of climate change wrought by the Ice Age. Ice Age oaks on the West Coast were far enough south to never have to contend with ice sheets, but could adapt to changing climate simply by shifting up and down a mountainside. California's topographical diversity allows for varying temperatures within a given region, so the oaks don't have to go far to cool off or warm up. Whereas in the relatively flatter Northeast, the oaks would have to travel farther distances to seek out different climates. In general, oaks aren't known for their lightness of foot, and no oak adapts instantaneously. But their regional distinctions serve to highlight the oak’s robustness – genetic diversity is the sign of ecological health, thriving in a variety of climates. But of course, it’s rarely that simple.

Quercus robur. By Johann Georg Sturm (Painter: Jacob Sturm)

Quercus robur. By Johann Georg Sturm (Painter: Jacob Sturm)


Back on the East Coast, it’s likely that Paul Gugger grew up in the midst of the red oak.

During his childhood in 1980s Northern New Jersey, Gugger spent his time running around the forests of his suburban home, poking into the surrounding wilderness that defined the border of his neighborhood. The red oak is New Jersey’s state tree, but that didn’t really matter to Gugger – at that time, it was more about catching animals and exploring. Later, as Gugger spent time in Durham, North Carolina studying biology, and later in Minneapolis, Minnesota pursuing his PhD in Ecology, oaks seemed to follow him around, in the landscape and the lab – his research at Duke was on maples, but the head of his lab there worked specifically with oaks and in the Twin Cities, his lab focused on oaks, while he worked on Douglas-firs. It wasn’t until coming out to California, to do his postdoc at UCLA with Victoria Sork’s lab, that Gugger set his research on oaks – and how they were changing in the midst of climate change.

Twenty species of oak are native to California, nine of which are endemic, meaning they are only found there. And because they’re also foundational species, California oaks are precious indicators of the ecological effects wrought by climate change – the entire ecosystem relies on oaks in some way.

In Sork’s lab, which focuses on the California valley oak (Quercus lobata), Gugger is investigating how the trees’ genetics are distributed geographically, in the hopes of identifying what kinds of genetic variations correlate with survival of climate change.

Certain traits indicate how a tree will respond to shifts in climate, such as when its flowers bloom, what temperatures it can withstand, and how it metabolizes water. But what strengthens the oak in some instances can also weigh it down, making it less genetically nimble in adapting. Oaks have a relatively long-term maturation phase (twenty or so years) and a slow speed dispersal rate, so they do not create freshly diversified generations quickly, or migrate easily. Climate change’s acceleration may outpace the oak, and Sork’s lab is examining what fighting (genetic) chance the valley oak has, before climate change nips it in the bud.

In any genetic study, pointing the finger at the precise gene for a precise, observable trait, is not easy, often because it just isn’t how genes work. The discrete physical results of a given genetic sequence can appear, or be stifled, by a variety of factors, depending on how sequences of genes work in concert with one another, or due to external influencers (or both). The entire scenario happening outside of an organism can have profound effects on how a gene is expressed inside (visible or not). And Gugger, within Sork’s lab, is focused on these invisible effects of climate change on the oak – how shifts in climate are changing the oak’s genome.

To sequence the oak’s genome in a lab requires, perhaps most importantly, patience. Oak generations line up roughly with human generations, so studying the complete lifespan of, say, an experimental cross-bred oak takes about as long as that researcher’s career. Important observations can be made within smaller chunks of that time, but the complete picture takes some time to develop. Gugger is working in Sork’s lab to understand both the invisible and visible aspects of an oak’s life, its genotypes (genetic sequences) and phenotypes (observable traits) over time. He hopes to scale this information up, to predict the lives of other oaks – and their likeliness of thriving within the world wrought by climate change.

From all over California, Gugger has gathered leaves and acorns from different regional oak populations to bring back to the lab at UCLA. There, the leaves can be used to understand what genetic variations exist based on location. The acorns have a good chance of ending up back in the ground, planted as part of the Common Garden experiment. By planting acorns from all over California in a consistent setting, the regional variable is held constant; in this context, any differences in appearance are driven by genetics, rather than environmental variation.

Cross-examination of the acorn data with genetic sequences from the leaves, helps Gugger and the lab gain a better understanding of how a genotype unfolds into a phenotype. What comes afterwards is a bit thornier – once the researchers understand what genotype works best where, and whether a given DNA sequence is associated with that region’s climate gradient, they have a solid predictor for which regions’ oak populations will falter, and which will thrive, due to imminent climate change. The question then becomes whether, and how, to intervene.
 

Quercus petraea, from Franz Eugen Köhler, Köhler's Medizinal-Pflanzen

Quercus petraea, from Franz Eugen Köhler, Köhler's Medizinal-Pflanzen

The term invasive species is usually tacked onto ecological villains, a stranger that wreaks havoc on a foreign ecological land, stressing local species’ defenses who are unprepared and unadapted to deal with the invaders. But the imminent (and perpetual) threat of climate change, and the ensuing thinning of genetic diversity for oaks that can’t stand the shifting tides, has encouraged Gugger and like-minded labs to consider extreme interventions.

If Sork’s lab determines which oak genomes thrive in which climates, then as a preemptive defense to climate change, it can enact what is known as assisted migration. This would mean actively, by human hands, relocating oak populations to more suitable regions in anticipation of a changing climate. Working unassisted, the oaks wouldn’t be able to migrate fast enough. If humans move them, the oaks’ genetic populations would be shuffled around. It might be good for the trees, but what about other local species? Introducing oaks could make them invasive– a recipe for potentially drastic ecological upheaval.

In this relatively extreme scenario, Gugger’s hands wouldn’t be the ones assisting the oak’s migration. In the lab, the point is to gather data and understand the originating context – not to make the laws, or enact policy. Ultimately it would be up to environmental codes and naturalist policies to decide whether or how to move oak populations around in response to climate change. The researcher’s role lies in excavating the best scientific evidence in defense or attack of such a policy.

And the policy effects of Gugger's research are loaded with economic, as well as environmental, incentives. Not only would compromising the US’s oak population dramatically change the country’s landscape, and the ecologies of each oak’s local biome, but it would also stand to have a grave impact on the commercial industries that rely on oak trees in some way. Prized for their hardiness and high tannin concentrations, which help resist fungal infections, North American oak varieties can become, for instance: lumber for construction, barrels for aging spirits, wood chips for smoking foods, and various alternative medicines.

If Gugger has one gripe for a common misunderstanding of genetics, it's the idea that there are clear-cut genetic instructions for every trait; that every phenotype has its discrete sequence of DNA.

For oaks, just as for any organism, genes just aren't that simple. They can be switched on or off by protein groups, react with one another in not-yet understood ways, and be changed within a given generation by environmental factors. But in a way, this is heartening. An oak's genotype is not static: just as the keystone population fluctuates on the shifting tides of ecology, so does a single oak's genetic code. The hope is that it survives the next season, and the violence of climate change, to keep doing so.

                                                      California oak tree, photo by vonriesling, via pixabay. 

                                                      California oak tree, photo by vonriesling, via pixabay

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Amelia Taylor-Hochberg:

Species: Homo sapiens

Habitat: Los Angeles, California

Diet: Omnivorous – Sandwiches, open-faced mostly.

Occupation: Journalist / editor

Contact: longhyphen@gmail.com

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