Wind patterns influence tree diversity across long distances

May 19, 2021
The winds that disperse a tree's pollen play a big part in tree diversity. (Pixabay/Couleur)

The winds that disperse a tree's pollen play a big part in tree diversity. (Pixabay/Couleur)

Wind currents may shape tree genetics more than previously thought, with implications for the future of trees in the midst of climate change, as pollen from those adapted to specific environments can reach distant areas where it may be unfavorable to other populations.

Prior research has suggested that wind could influence genetic variation in trees, but those studies examined only small areas. Now, researchers from the University of California, Berkeley, have drawn on new windscape models and genetic data to reveal for the first time how differing wind patterns can foster corresponding genetic-variation trends within many tree species across long distances. The findings were detailed in a study published April 27 in PNAS.

To reach these conclusions, lead author Matthew Kling, a postdoctoral researcher in biology at UC Berkeley, and his co-author at the same institution, David Ackerly, mapped the location of over 1,900 tree and shrub populations, including 97 different species. The researchers then applied a wind-connectivity model to these points to help predict how seeds and pollen–carrying genetic information should be moving within these populations.

Once they established the flow of pollen, the researchers drew on genetic data to determine how seeds and pollen were really moving among tree populations and then later compared these results to the wind-based predictions. 

Tree populations downwind from others tended to be more genetically diverse, while trees connected by strong currents were more genetically alike. Those connected by imbalanced winds were more genetically asymmetrical, meaning trees with less wind linking them together were less similar genetically.

For example, northern and eastern populations of silver birch, a medium-sized deciduous tree found in Europe and parts of Asia, tend to be downwind from most other populations, inhabiting a kind of pollen "sink" that fosters more genetic variation over time.  

The study arose from a desire to understand the vulnerability of biodiversity to climate change and human activity, Kling said. As environments change due to these factors, the organisms that inhabit them, including trees, may need to migrate to remain in the climatic conditions in which they've evolved. 

This migration may not come easily, as other research has shown that North American trees are struggling to expand their range, currently inhabiting only half the land they should under contemporary climate conditions. Obstacles such as mountain ranges, parasites and predation and even the slow nature of tree expansion limit a species' mobility. 

One of Kling's previous studies dealing with climate change and wind predicted that wind-dispersed trees in tropical regions and those living on the leeward side of mountains may be more vulnerable to climate change, because they may not be able to spread their pollen to more climatically appropriate areas.

"If the wind is blowing in the right direction to move the genes and move the species range to where they want to go, then that's going to help them," Kling said in an interview with The Academic Times. "But the wind could also be blowing in the wrong direction. That's going to actually kind of hinder the ability of pollen and seeds to move where they would naturally need to move in order to adapt to climate change."

Trees themselves may not be mobile, but winds can carry pollen and seeds up to 1,800 miles, at least for some pines. Because climate conditions vary, the winds can foster disparate adaptations within one tree species that grows in various regions. When wind sweeps pollen from one population from one region to another, it moves that genetic information as well, with potentially negative results.

For example, wind currents may spread the pollen from trees in a warm region to reproduce with those in a colder one. This process could produce a baby tree that possesses features from a warm-zone father and a cold-zone mother. With the father's influence, the baby could leaf out earlier than it is supposed to, leaving it vulnerable to frost damage in the frigid environment. Trees bred to grow quickly may also be sensitive to climate change, because the genes that dictate growth time and height also govern cold resistance.

But with climate change, some of these adaptations could be advantageous in the long run.

Kling and Ackerly did not set out to confirm any such adaptation, given the data available. The genetic material they analyzed was neutral or mostly neutral; it didn't code for any adaptations. According to Kling, there isn't a great depth of knowledge on how different parts of the genome function for most species, aside from fruit flies, mice and humans. This lack of understanding is especially true for trees. 

"In an ideal world, we would have all that information," Kling said. "We'd be able to do a much more in-depth analysis of how these processes of the way the different parts of the genome that are actually doing things are moving and shaping the evolution of all these populations. And maybe someday we'll get there, but the data just isn't at that stage yet in this field."

Having demonstrated that wind patterns do shape gene flow between tree populations, Kling wants to combine this genetic work with some of his previous research on wind, trees and climate change to see how individual species may be affected.

The study, "Global wind patterns shape genetic differentiation, asymmetric gene flow, and genetic diversity in trees," published April 27 in PNAS, was authored by Matthew M. Kling and David D. Ackerly, University of California, Berkeley.

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