A new study, based at the University of Alberta, released this week, indicates that natural selection may be making the mountain pine beetle more tolerant of colder temperatures and that the beetle may be evolving the ability to fly longer distances.
A second study, from the Colorado School of Mines, also released this week, is tracking how the extent of pine beetle infected or killed trees in forests is changing ground water and stream flows.
The mountain pine beetle infestation has wreaked havoc in North America, across forests from the American Southwest to British Columbia and Alberta. Millions of hectares of forest have been lost, with severe economic and ecological impacts from a beetle outbreak ten times larger than previous ones.
Dust from beetle killed wood is believed partially responsible for the explosions at the Lakeland Mill in Prince George and the Babine Forest Products mill in Burns Lake. The explosion in early 2012 at the Babine Forest Products mill killed two workers and injured another twenty. The Lakeland Mill explosion killed two workers and injured twenty four others.
As part of the fight to contain the mountain pine beetle, scientists recently sequenced the pine beetle genome.
Using that genome, Jasmine Janes and colleagues at the University of Alberta, with assistance from the University of British Columbia and the University of Northern British Columbia, used genetics to track how the pine beetle was able to expand its range so rapidly. The study was published in Molecular Biology and Evolution.
Studied at molecular level
While teams of researchers have tracked the path of the pine beetle across BC on the ground, how the beetle spread so easily “is only beginning to be understood at the molecular level,” the study says.
Pine beetles were collected from 27 sites in Alberta and British Columbia. The University of Alberta scientists were especially interested in how the pine beetle was able to jump across the Rockies, something that earlier researchers believed would not happen.
By looking at the genetic markers, the team concluded that the pine beetle may have been able to spread by adjusting its cellular and metabolic functions to better withstand cooler climates and facilitate a larger geographic dispersal area.
In an e-mail to Northwest Coast Energy News, Janes said the research looked at genomic signatures to find out how the beetle had been able to spread into Alberta – where did it come from, what route did it take and how did it overcome the physical and climatic barriers that we had always assumed?
The research discovered that there are two genetically different populations of pine beetles, one from the south of British Columbia and Alberta and one in the north. Another group of pine beetles, found near Valemount, “were harder to classify as being from either north or south genetically. The beetles in this area were showing higher genetic diversity.”
The pine beetle has always been around and killed older trees (called “low quality hosts”), helping to renew the ecosystem. There were also larger five-year infestations that occurred on a 20 to 40 year cycle. The current pine beetle “epidemic” in BC has gone on now for more than 20 years, with the pine beetle “observed in previously unrecorded numbers” over a much wider area
It is generally believed that climate change has help the pine beetle survive milder winters.
The study notes:
Successful establishment of mountain pine beetle on pure jack pine in northern Alberta has raised concerns that the mountain pine beetle will continue to expand its range into the vast boreal forest of jack pine that extends across North America from the Northwest Territories to the Atlantic Coast.
The teams concludes that one group of the beetles originated in southwestern BC perhaps from Whistler or Manning Park. Then the beetles spread north up the west coast of BC toward Houston “with rapid population size increases in central and northern BC and then dispersed long distances with prevailing winds toward the east and Alberta.”
Some of the beetles from southwestern BC appear to have taken a different route, moving more slowly eastward in the south of BC toward Crowsnest Pass area and then moving northward along the base of the Rockies, Janes said, adding. “Our research suggests that these two routes have then met in the middle again, around Valemount and that is why we see the genetic patterns across the landscape that we observed.”
Selective pressure
The second part of the research was answering the question of how the beetles were able to do this. How could they withstand the colder temperatures to spread further north and east?
To answer the scientists used the same genetic markers (single nucleotide polymorphisms) to conduct “selective sweeps” of the beetle genome. The sweeps look for unusual genetic markers that could indicate the beetles are under “selective pressure.”
The study looked at specific functions in the beetle: the genes that govern “actin filaments” that “control muscle contractions like shivering and moving wings”; “the synthesis of cholesterol that provides energy for metabolic activities” and transport of ions across cell membranes.
Normally, female pine beetles can only fly short distances to find a new host tree to lay eggs. They can travel longer distances if they are up in the tree canopy and are then carried by the wind. Stronger pine beetles that can fly longer distances show the threat is likely evolving.
The study concludes that Canadian Mountain Pine Beetle range expansion:
may continue as populations are currently exhibiting signals of selection. These signals suggest ongoing adaptation of metabolic and cellular processes that could potentially allow them to withstand colder temperatures, shift developmental timing and facilitate longer dispersal flights.
Janes said further research is required to fully validate and understand these signatures of selection, but it does suggest that the beetle is adapting and that is why it “may have been able to breach the Rocky Mountains”
Water and trees
The Colorado study asked how all those dead trees are changing stream flow and water quality?
“The unprecedented tree deaths caused by these beetles provided a new approach to estimating the interaction of trees with the water cycle in mountain headwaters like those of the Colorado and Platte Rivers,” said Reed Maxwell a hydrologist at the Colorado School of Mines.
Maxwell and colleagues have published results of their study of beetle effects on stream flows in this week’s issue of the journal Nature Climate Change.
As the trees die, they stop taking up water from the soil, known as transpiration. Transpiration is the process of water movement through a plant and its evaporation from leaves, stems and flowers.
The “unused” water then becomes part of the local groundwater and leads to increased water flows in nearby streams.
“Large-scale tree death due to pine beetles has many negative effects,” says Tom Torgersen of the US National Science Foundation’s Directorate for Geosciences and program director for the NSF’s Water, Sustainability and Climate program.
“This loss of trees increases groundwater flow and water availability, seemingly a positive,” Torgersen says.
“The total effect, however, of the extensive tree death and increased water flow has to be evaluated for how much of an increase, when does such an increase occur, and what’s the water quality of the resulting flow?”
Under normal circumstances, green trees use shallow groundwater in late summer for transpiration.
Red- and gray-phase trees–those affected by beetle infestations–stop transpiring, leading to higher water tables and greater water availability for groundwater flow to streams.
The Colorado study shows that the fraction of late-summer groundwater flows from affected watersheds is about 30 per cent higher after beetles have infested an area, compared with watersheds with less severe beetle attacks.
“Water budget analysis confirms that transpiration loss resulting from beetle kill can account for the increase in groundwater contributions to streams,” write Maxwell and scientists Lindsay Bearup and John McCray of the Colorado School of Mines, and David Clow of the U.S. Geological Survey, in their paper.
Dead trees create changes in water quality
“Using ‘fingerprints’ of different water sources, defined by the sources’ water chemistry, we found that a higher fraction of late-summer stream flow in affected watersheds comes from groundwater rather than surface flows,” says Bearup.
“Increases in stream flow and groundwater levels are very hard to detect because of fluctuations from changes in climate and in topography. Our approach using water chemistry allows us to ‘dissect’ the water in streams and better understand its source.”
With millions of dead trees, adds Maxwell, “we asked: What’s the potential effect if the trees stop using water? Our findings not only identify this change, but quantify how much water trees use.”
An important implication of the research, Bearup says, is that the change can alter water quality.
The new results, she says, help explain earlier work by Colorado School of Mines scientists. “That research found an unexpected spike in carcinogenic disinfection by-products in late summer in water treatment plants.”
Where were those water treatment plants located? In bark beetle-infested watersheds.
The TRIA project (a collaboration of researchers at the University of Alberta, University of British Columbia, University of Montreal, University of Northern British Columbia). The TRIA project investigates the physiology, genetics and ecology of all three players in the mountain pine beetle system – the pines (lodgepole and jack pine, and their hybrids), the beetle and the fungus (several types).
The Colorado study is funded by the National Science Foundation’s (NSF) Water, Sustainability and Climate (WSC) Program. WSC is part of NSF’s Science, Engineering and Education for Sustainability initiative.
Map showing the area of the UBC climate change study. The squares show areas used for “spatial comparison of temperature and zonation.” The circles were used for comparison. (Science)