Never too late to mate? Evolution of timing of attraction as a driver of species diversification

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The world around you changes in a daily rhythm: The light and warmth of the day is superseded by the darkness and chill of the night. Most moth females will fill the air with their pheromone only at night. It is almost impossible to find a healthy meal at 4 in the morning.It is beneficial for any living being to acquire a 24-hours rhythm to predict these environmental changes and cope with them (e.g. by moth males searching for females only at night und many humans eating during the day). Hence it is no surprise that almost all organisms do show a daily rhythm of their life processes, e.g. the sleep-wake cycle, based on an internal circadian clock. Even though the environmental changes in a given habitat are the same for all inhabitants, some species have evolved to be day-active, while others are night-active. Even closely related species living in the same habitat can differ from each other in their daily activity rhythms. Despite a growing knowledge on the molecular basis of circadian rhythms, the evolution of differentiation in daily activity patterns is largely unexplored. Which molecular changes underlie a change in the timing of behavior? Do molecular changes lead to the same phenotype in males and females, or is there a sex-specificity for some changes? If timing has changed in one population, could this effectively prevent individuals from this population from mating with individuals from a different population, ultimately driving the formation of new species?The noctuid moth Spodoptera frugiperda is an ideal organism to address these questions. It occurs as two sympatric strains that differ in their timing of mating behavior: The so-called corn-strain mates early in the night while the so-called rice-strain mates late in the night. It is hypothesized that the strains are undergoing speciation in sympatry and that their temporal differentiation plays a key role in this process.In this proposed project, we will determine the temporal isolation present in the field by quantifying strain-specific differences in timing of behavior and circadian rhythm genes in different populations. We will also identify the genetic basis of the timing differentiation by fine-scale mapping using RAD sequences of different male-informative backcrosses. The resulting candidate gene(s) will be functionally characterized by editing them using CRISPR/Cas9 and analyzing resulting gene expression and behavioral differences. As sex-specific expression differences are one possible mechanism that could underlie the timing diversification, we will also compare clock gene expression between males and females.In summary, this project will shed light on the molecular mechanisms underlying temporal isolation in Spodoptera frugiperda and evaluate the contribution of the temporal isolation to the strain divergence. It will advance our understanding of speciation in the face of gene flow and of the evolution of differential timing of (mating) behavior.