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Title: Explaining the sawtooth: Latitudinal periodicity in a circadian gene correlates with shifts in generation number

item LEVY, REBECCA - Tufts University
item KOZAK, GENEVIEVE - Tufts University
item WADSWORTH, CHRISTA - Tufts University
item Coates, Brad
item DOPMAN, ERIK - Tufts University

Submitted to: Journal of Evolutionary Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2014
Publication Date: 1/1/2015
Citation: Levy, R.C., Kozak, G.M., Wadsworth, C.B., Coates, B.S., Dopman, E.B. 2015. Explaining the sawtooth: Latitudinal periodicity in a circadian gene correlates with shifts in generation number. Journal of Evolutionary Biology. 28(1):40-53.

Interpretive Summary: The number of mating generations insects produce per crop growing season is related to environmental conditions. The level of crop damage tends to increase as insect generation numbers increase. A USDA Scientist in collaboration with university researchers provide genetic data that suggests that the number of generations in the European corn borer populations in the United States is strongly correlated with variation in genes that control circadian rhythms. These data are important for understanding how insect generation number is determined, and may provide insight into how the genetics of insect populations might change in response to climate change and how these changes might affect the associated levels of crop damage.

Technical Abstract: Many species in temperate climates show latitudinal variation in life-cycle corresponding to synchronization with seasonal fluctuations in resources. In particular, insects often vary clinally in voltinism (the number of generations per year) which is determined by the timing of diapause termination. These phenotypic gradients in life-cycle have rarely been linked to genetic variation at specific loci. We studied genetic variation along a latitudinal cline in the European corn borer (Ostrinia nubilalis), which varies in the number of generations per year in the United States, from one generation in the north to three or more in the south. We found that voltinism is closely associated with allelic variation in cryptochrome, a gene in the circadian clock pathway. Period, another circadian gene, showed a sawtooth cline and varied both between voltinism types and within the bivoltine type. Our study suggests that these circadian genes are key to seasonal timing and may be involved in variation in diapause termination, traits which are associated with temporal isolation between Ostrinia strains.