title: Seasonal cues induce phenotypic plasticity of Drosophila suzukii to enhance winter survival.
abstract: BACKGROUND
  As global climate change and exponential human population growth intensifies pressure on agricultural systems, the need to effectively manage invasive insect pests is becoming increasingly important to global food security. Drosophila suzukii is an invasive pest that drastically expanded its global range in a very short time since 2008, spreading to most areas in North America and many countries in Europe and South America. Preliminary ecological modeling predicted a more restricted distribution and, for this reason, the invasion of D. suzukii to northern temperate regions is especially unexpected. Investigating D. suzukii phenology and seasonal adaptations can lead to a better understanding of the mechanisms through which insects express phenotypic plasticity, which likely enables invasive species to successfully colonize a wide range of environments.
  
  
  RESULTS
  We describe seasonal phenotypic plasticity in field populations of D. suzukii. Specifically, we observed a trend of higher proportions of flies with the winter morph phenotype, characterized by darker pigmentation and longer wing length, as summer progresses to winter. A laboratory-simulated winter photoperiod and temperature (12:12 L:D and 10 °C) were sufficient to induce the winter morph phenotype in D. suzukii. This winter morph is associated with increased survival at 1 °C when compared to the summer morph, thus explaining the ability of D. suzukii to survive cold winters. We then used RNA sequencing to identify gene expression differences underlying seasonal differences in D. suzukii physiology. Winter morph gene expression is consistent with known mechanisms of cold-hardening such as adjustments to ion transport and up-regulation of carbohydrate metabolism. In addition, transcripts involved in oogenesis and DNA replication were down-regulated in the winter morph, providing the first molecular evidence of a reproductive diapause in D. suzukii.
  
  
  CONCLUSIONS
  To date, D. suzukii cold resistance studies suggest that this species cannot overwinter in northern locations, e.g. Canada, even though they are established pests in these regions. Combining physiological investigations with RNA sequencing, we present potential mechanisms by which D. suzukii can overwinter in these regions. This work may contribute to more accurate population models that incorporate seasonal variation in physiological parameters, leading to development of better management strategies.
authors.affiliation: Mid-Columbia Agricultural Research and Extension Center, Oregon State University, 3005 Experiment Station Drive, Hood River, OR, 97331, USA.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Shearer
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, CA, 95616, USA.
authors.forename: Jessica D
authors.initials: JD
authors.lastname: West
authors.affiliation: Department of Horticulture, Oregon State University, Corvallis, OR, 97331, USA.
authors.forename: Vaughn M
authors.initials: VM
authors.lastname: Walton
authors.affiliation: Mid-Columbia Agricultural Research and Extension Center, Oregon State University, 3005 Experiment Station Drive, Hood River, OR, 97331, USA.
authors.forename: Preston H
authors.initials: PH
authors.lastname: Brown
authors.affiliation: Department of Evolution and Ecology, University of California, Davis, CA, 95616, USA.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Svetec
authors.affiliation: Department of Entomology and Nematology, University of California, Davis, CA, 95616, USA. jcchiu@ucdavis.edu.
authors.forename: Joanna C
authors.initials: JC
authors.lastname: Chiu
mesh_terms: D000064:Acclimatization; D000818:Animals; D003080:Cold Temperature; D004330:Drosophila / Q000502:physiology*; D005260:Female; D007300:Insect Control; D008297:Male; D010641:Phenotype; D012621:Seasons
keywords: Cold tolerance; Diapause; Drosophila suzukii; High-throughput sequencing; Phenotypic plasticity; Transcriptome