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Texas A&M scientists begin southern pine beetle genome sequencing

Texas A&M AgriLife Research is leading research to stop the southern pine beetle in its tracks, or at least be able to predict what is causing outbreaks of the tree-killer outside of its historical range.

Dr. Claudio Casola, an AgriLife Research forest genomics assistant professor in the Texas A&M University ecosystem science and management department in College Station, has received funding from The Eppley Foundation for Research to sequence the genome of the southern pine beetle.

The SPB routinely destroys pine forests in the U.S. and overall has been responsible for more than $1.5 billion in losses. Casola said this species has been moving north because of climate change.

"My goal is to understand the beetle's biology, which will help us fight large outbreaks," he said. "Eventually, this work will help in designing tools to improve monitoring of the beetles, predicting outbreaks, and more importantly, controlling population bursts typical of outbreaks."

Casola said most bark beetles inhabit dying or weakened trees and have a beneficial impact on forest health by accelerating forest succession. However, several bark beetle species experience population outbreaks that kill living trees.

Dendroctonus frontalis, also known as the southern pine beetle or SPB, is the most damaging forest pest in the southeastern U.S., he said. Outbreaks primarily affect loblolly pine, which forms 80% of the planted forestland and over one-half of the standing volume of trees in the southern U.S.

"Identifying the genomic basis of outbreaks in an aggressive tree killer, the southern pine beetle (SPB)" is the name of the project. Joining Casola will be Dr. Heath Blackmon, assistant professor, Texas A&M University department of biology, College Station.

"The benefits of this project extend beyond the immediate goals of providing resources that allow for better management of a forest pest," Blackmon said. "The genus Dendroctonus contains 20 species of which only a subset are pests.

"Many of these bark beetles have striking changes in either the number of chromosomes or the type of sex chromosomes they have. One of our long-term goals is to use the genome assembly created for the SPB as a foundation for future analyses of other species in the genus."

Casola said the SPB is increasingly threatening pine forests across Central and North America, recently colonizing previously unaffected areas north of its historical range, including outbreaks in New Jersey and New York.

"Previously unaffected forests are likely to be more susceptible to SPB attacks because of the lack of natural defenses found in trees exposed to this pest in its native range," he said. "SPB's northward progression could lead to forest destruction comparable to those experienced in the western U.S. and Canada in the ongoing outbreak of the mountain pine beetle."

Along with timber loss, the repercussions of large-scale forest destruction include ecosystem degradation, hydrological instability and reduced carbon sequestration, Casola said.

"While there have been strategies to predict, monitor and suppress SPB outbreaks before, they have been applied with limited success," he said. "A major hurdle in managing SPB is the current inability to explain and predict outbreaks."

Casola said it is not clear if different populations of beetles vary in their propensity to form massive groups leading to outbreaks.

The AgriLife Research study will investigate for the first time the genomic basis of bark beetle infestation behavior, he said. It will also introduce advanced whole-genome sequencing approaches never applied in the southern pine beetle.

"A critical impediment is the lack of genetic and genomic resources in this species," he said. "That's why our efforts are concentrated on discovering the genetic basis of SPB infestation behavior leading to outbreaks."

Casola is an expert in comparative and population genomic analyses. He has collaborated on genome sequencing and analyses of multiple animal and plant species. His research focuses on the genome-wide comparative study of gene and gene-family evolution.

Blackmon is an expert in beetle collection, taxonomic identification, DNA extraction and genome sequencing and analysis. He has led or co-authored 12 studies of genome and sexual system evolution over the past five years.

Casola and Blackmon will generate the first SPB reference genome, a resource that will be compared with other beetle genomes to better understand the molecular basis of the tree-killing behavior in this pest insect.

"The reference genome will help compare the genetic makeup of SPB populations responsible for outbreaks with those found nearby outbreak areas. This will tell us if outbreaks mainly spawn from local endemic populations or if dispersal from other areas play a major role in these large infestations," he said.

Ongoing collaborations with the U.S. Department of Agriculture Forest Service Southern Research Station will ensure the collection of the required SPB samples from outbreak and non-outbreak SPB populations.

Molecular and bioinformatic analyses will be performed in Casola's and Blackmon's laboratories, as well as DNA sequencing at the Texas A&M AgriLife Genomics and Bioinformatics Service and the High-Performance Research Computing facility at Texas A&M.

Casola said this project should impact the way other forest entomologists monitor and study the southern pine beetle and other forest pests in North America.

Provided by Texas A&M University