Genetic basis of allochronic differentiation in the fall armyworm

Abstract

BackgroundVery 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.ResultsThrough 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.ConclusionsTogether, 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0911-5) contains supplementary material, which is available to authorized users.

Divergent selection causes whole genome differentiation without physical linkage among the targets in Spodoptera frugiperda (Noctuidae)

“…Interestingly, cyc gene, which plays a key role in circadian clock (Rutila et al 1998), is also included in the list of the potentially adaptively evolved genes. Thus, divergent selection on cyc might be responsible for pre-mating reproductive isolation due to allochronic mating time (Schöfl et al 2009;Hänniger et al 2017).…”

“…A QTL study shows that genetic variations in vrille gene can explain differentiated allochronic mating behavior in S. frugiperda (Hänniger et al 2017). This gene is not found in the outliers.…”

“…As this level of genomic differentiation is one of the lowest among reported cases, and hybrids are frequently generated (Prowell et al 2004), these two strains an ideal system to explore critical evolutionary forces for genomic differentiation in the presence of gene flow. Whole genome differentiation between sfC and sfR might involve both premating reproductive isolation through assortative mating (Schöfl et al 2009;Unbehend et al 2013;Hänniger et al 2017), or postmating reproductive isolation by ecological divergent selection, or by reduced hybrid fertility (Dumas, Legeai, et al 2015).…”

Differences in gene regulation in a tephritid model of prezygotic reproductive isolation

“…One is a tephritid, Bactrocera cucurbitae , in which cry mRNA is more abundant during the photophase in an early than a late mating strain (Fuchikawa et al , ). The second is a noctuid moth in which vrille mRNA is more abundant in a late than an early mating strain (Hanniger et al , ).…”

Assessing genomic admixture between cryptic Plutella moth species following secondary contact

“…Reproductive barriers can maintain boundaries between sympatric congeneric animal species (cryptic or non-cryptic) using a range of isolating mechanisms such as olfaction, pheromone cues and mating calls (Andersson, et al 2007;Jones and Hamilton 1998), host plant preference or mating timing (Hänniger, et al 2017), and endosymbiont infection (Bordenstein, et al 2001;Shoemaker, et al 1999). Although these factors can impose reproductive isolation barriers and restrict hybridization, assortative mating does not always occur (Mallet, et al 2007).…”