Abstract Detail

Population Genetics/Genomics

Steele, Stephanie [1], Ryder, Oliver [2], Maschinski, Joyce [3].

RNA-Seq as a tool to assess adaptive genetic variation and evolutionary potential for bark beetle response in the rare Torrey pine.

For many conifer populations, prolonged drought and warmer temperatures due to climate change have increased evapotranspirative stress and created favorable conditions for bark beetle outbreaks.  The ability of tree species to adapt to these challenges may increase with population size and the degree of standing genetic variation, calling into question the resilience of small, rare plant populations.  The Torrey pine (Pinus torreyana Parry) is the rarest pine in North America, occurring naturally in one mainland and one island population in southern California.  Recently, the mainland population has experienced several declines, likely due to drought stress and increased incidence of attack by the Ips paraconfusus bark beetle.  While past allozyme and chloroplast studies have indicated within-population monomorphism and few between-population differences, the species would benefit from an assessment of potential adaptive diversity throughout the genome.  Here, we use RNA-Seq to survey trancriptome-wide diversity across 40 individuals to 1) characterize patterns of functional genetic diversity in the species and 2) test for genetic differentiation between trees that succumbed to beetle attack or survived following an outbreak.  Consistent with previous studies, we found low genetic variation (9599 SNPs across transcripts), with most SNPs occurring as fixed differences between populations.  However, we found structure within the mainland and polymorphisms segregating in both populations.  Interestingly, we found differentiation in multivariate genotypes between attacked and surviving trees, and 11 SNPs significantly associated with survival status, including SNPs in genes with putative roles in defense and water regulation.  Gene ontology analysis among the top 10% of SNP associations revealed an enrichment of defense-related functions relative to the genome-wide background.  While low genetic diversity suggests limited adaptive capacity, genetic associations with survival in functionally relevant genes suggest that surviving trees are a non-random subset of the population, indicating evolutionary potential for bark beetle defense.  This initial study prompts future research to dissect the genetic basis of resistance phenotypes and suggests that conservation efforts should protect surviving genotypes to aid adaptation to future beetle outbreaks.

1 - San Diego Zoo Institute for Conservation Research, Plant Conservation, 15600 San Pasqual Valley Rd, Escondido, CA, 92027, USA
2 - San Diego Zoo Institute for Conservation Research, Conservation Genetics, 15600 San Pasqual Valley Rd, Escondido, CA, 92027, United States
3 - San Diego Zoo Institute for Conservation Research, Plant Conservation, 15600 San Pasqual Valley Rd, Escondido, CA, 92027, United States

Torrey pines
Bark beetles
genetic diversity
Evolutionary potential
Plant Defense.

Presentation Type: Poster
Session: P, Population Genetics/Genomics Posters
Location: Virtual/Virtual
Date: Thursday, July 30th, 2020
Time: 5:00 PM Time and date to be determined
Number: PPG009
Abstract ID:872
Candidate for Awards:None

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