Chasing sympatric speciation: The relative importance and genetic basis of prezygotic isolation barriers in diverging populations of Spodoptera frugiperda

This thesis investigates the mechanisms underlying three prezygotic isolation barriers between the corn- and the rice-strain of the noctuid moth Spodoptera frugiperda to determine possible interactions between these isolation barriers and their relative importance for sympatric speciation.
First, we investigated the role of host plant differentiation as isolation barrier between the two strains.
Our analysis shows that, although there is some host-associated genetic structure, host plant differentiation alone cannot explain the total genetic variance and thus other, additional factors must maintain the genetic differentiation.
Second, we focused on differentiation in sexual communication between the two strains. Females emit a strain-specific sex pheromone blend, but males do not show a preference for the blend of their own strain.
The third and most consistent prezygotic isolation barrier between the two strains is allochronic differentiation, i.e. the strains differ in the daily timing of their sexual activities. We found one major QTL for the circadian differentiation, the circadian clock gene vrille maps to this locus, which is thus the major candidate gene underlying this circadian differentiation.
Finally, I discuss the evolutionary potential of the different isolation barriers and I propose an interaction between all prezygotic mating barriers which facilitate the divergence of the two strains, with allochronic differentiation being the driving force.
In conclusion, by investigating the prezygotic isolation barriers between two sympatric strains of S. frugiperda in detail, I have determined their strengths and possible interactions, giving insights in the mechanisms underlying and facilitating the process of sympatric speciation.