Allochronic Separation versus Mate Choice: Nonrandom Patterns of Mating between Fall Armyworm Host Strains

Abstract

Assortative mating may result from intrinsic individual mating preferences or from assortment traits not requiring expression of preferences. Assortment traits are phenotypes expressed in both sexes that enhance the probability of encountering individuals possessing similar trait values. In the noctuid moth Spodoptera frugiperda, it has been suggested that nonrandom mating between two host strains is caused by a temporal assortment trait-that is, differential timing of calling and copulation during the night. By experimental manipulation of this trait in controlled mate-choice experiments, we investigated whether mating by same-strain individuals is enhanced mainly by the allochronic shift of mating activity or is also affected by time-independent intrinsic mating preferences. The observed patterns suggest that nonrandom mating between the two host strains in the laboratory is shaped by an interaction of both effects that is dominated by mating preferences during the first encounter night. This interaction changes over time as the preferences become weaker on subsequent nights. Males were less restricted than females with regard to both the time shift in mating activity and mate preferences. Although the nature of the mate-preference mechanism remains elusive, its restriction to females suggests that male-produced close-range pheromones emitted during courtship play a role.

Difference in diel mating time contributes to assortative mating between host plant-associated populations of Chilo suppressalis

“…Therefore, following Korol et al . and Schöfl et al 2342,. a maximum-likelihood modeling approach was adopted to evaluate the respective contributions of divergence in the diel timing of mating activity and mate preference.…”

“…We did this by rearing part of the third generation W population in another insectarium at the same temperature and humidity as the original insectarium, but, following the method described by Miyatake et al 12. and Schöfl et al 23,. under a photoperiod in which the scotophase began 3 h earlier.…”

“…The second method was, following Schöfl et al 23,. to confine single choice tests to the latter part of the scotophase.…”

“…The built-in statistical analysis program in this software estimated the significance of PTI and I PSI by resampling 10,000 times and providing average PTI and I PSI values3741. Following Schöfl et al 23,. we used a G–test to test whether the proportions of the four potential mating combinations were significantly different.…”

“…Although it has been suggested that differences in diel mating time can potentially induce allochronic reproductive isolation between laboratory-bred strains of the same species12, closely related species20, and host-associated populations2122, the evidence for this has so far been relatively equivocal. For example, although the rice and corn strains of Spodoptera frugiperda have different diel mating times, this is not the main reason for the reproductive isolation observed between these two strains in the wild2324. There is still no evidence that divergence in diel mating time is a significant factor in the reproductive isolation of sympatric, conspecific populations.…”