Abstract

Organisms use endogenous clocks to anticipate regular environmental cycles, such as days and tides. Natural variants resulting in differently timed behaviour or physiology, known as chronotypes in humans, have not been well characterized at the molecular level. We sequenced the genome of Clunio marinus, a marine midge whose reproduction is timed by circadian and circalunar clocks. Midges from different locations show strain-specific genetic timing adaptations. We examined genetic variation in five C. marinus strains from different locations and mapped quantitative trait loci for circalunar and circadian chronotypes. The region most strongly associated with circadian chronotypes generates strain-specific differences in the abundance of calcium/calmodulin-dependent kinase II.1 (CaMKII.1) splice variants. As equivalent variants were shown to alter CaMKII activity in Drosophila melanogaster, and C. marinus (Cma)-CaMKII.1 increases the transcriptional activity of the dimer of the circadian proteins Cma-CLOCK and Cma-CYCLE, we suggest that modulation of alternative splicing is a mechanism for natural adaptation in circadian timing.Supplementary informationThe online version of this article (doi:10.1038/nature20151) contains supplementary material, which is available to authorized users.

Highlights

  • Organisms use endogenous clocks to anticipate regular environmental cycles, such as days and tides

  • C. marinus strains from different locations (Extended Data Fig. 1a) show local adaptation in circadian and circalunar emergence times (Extended Data Fig. 1b, c)

  • Assuming that the alleles associated with timing adaptation probably We investigated how polymorphisms in the C. marinus (Cma)-CaMKII.[1] locus originated from standing genetic variation (Supplementary Note 5), affect the enzyme

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Summary

Introduction

Organisms use endogenous clocks to anticipate regular environmental cycles, such as days and tides. We examined genetic variation in five C. marinus strains from different locations and mapped quantitative trait loci for circalunar and circadian chronotypes. In D. melanogaster, polymorphisms in the core circadian clock genes period, timeless and cryptochrome are associated with adaptive differences in temperature compensation[7], photo-responsiveness of the circadian clock[8] and emergence rhythms[9]. While these studies offer insights into the evolution of known circadianclock molecules, genome-wide association studies[10,11] and other forward genetic approaches As a starting point for these analyses, we sequenced, assembled, mapped and annotated a C. marinus reference genome

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