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Abstract:
Background: Very little is known on how changes in circadian rhythms evolve. The noctuid moth Spodoptera
frugiperda (Lepidoptera: Noctuidae) consists of two strains that exhibit allochronic differentiation in their mating
time, which acts as a premating isolation barrier between the strains. We investigated the genetic basis of the
strain-specific timing differences to identify the molecular mechanisms of differentiation in circadian rhythms.
Results: Through QTL analyses we identified one major Quantitative trait chromosome (QTC) underlying
differentiation in circadian timing of mating activity. Using RADtags, we identified this QTC to be homologous to
Bombyx mori C27, on which the clock gene vrille is located, which thus became the major candidate gene. In S.
frugiperda, vrille showed strain-specific polymorphisms. Also, vrille expression differed significantly between the
strains, with the rice-strain showing higher expression levels than the corn-strain. In addition, RT-qPCR experiments
with the other main clock genes showed that pdp1, antagonist of vrille in the modulatory feedback loop of the
circadian clock, showed higher expression levels in the rice-strain than in the corn-strain.
Conclusions: Together, our results indicate that the allochronic differentiation in the two strains of S. frugiperda is
associated with differential transcription of vrille or a cis-acting gene close to vrille, which contributes to the evolution of prezygotic isolation in S. frugiperda.
