Abstract
Speciation often involves the coupling of multiple isolating barriers to produce reproductive isolation, but how coupling is generated among different premating barriers is unknown. We measure the degree of coupling between the daily mating time and seasonal mating time between strains of European corn borer (Ostrinia nubilalis) and evaluate the hypothesis that the coupling of different forms of allochrony is due to a shared genetic architecture, involving genes with pleiotropic effects on both timing phenotypes. We measure differences in gene expression at peak mating times and compare these genes to previously identified candidates that are associated with changes in seasonal mating time between the corn borer strains. We find that the E strain, which mates earlier in the season, also mates 2.7 h earlier in the night than the Z strain. Earlier daily mating is correlated with the differences in expression of the circadian clock genes cycle, slimb, and vrille. However, different circadian clock genes associate with daily and seasonal timing, suggesting that the coupling of timing traits is maintained by natural selection rather than pleiotropy. Juvenile hormone gene expression was associated with both types of timing, suggesting that circadian genes activate common downstream modules that may impose constraint on future evolution of these traits.
Highlights
Speciation typically occurs through the accumulation of multiple reproductive barriers [1,2].The evolution of reproductive isolation is tied to the coupling of different barrier traits that produce increased isolation when acting together when compared to each acting separately [3,4]
We investigate differences in the daily mating time between E and Z European corn borer moth (ECB) strains that have been previously characterized for differences in seasonal timing
The BE stock was originally derived from bivoltine E strain individuals collected from Geneva, NY (42.8680◦ N, 76.9856◦ W) and the UZ stock from univoltine Z strain individuals that were collected from Bouckville, NY (42.8892◦ N, 75.5513◦ W)
Summary
Speciation typically occurs through the accumulation of multiple reproductive barriers [1,2]. The evolution of reproductive isolation is tied to the coupling of different barrier traits that produce increased isolation when acting together when compared to each acting separately [3,4]. We understand how coupling between prezygotic and postzygotic isolation occurs through indirect selection during reinforcement [5], the mechanisms that produce coupling between different prezygotic barriers are largely unexplored [3]. It is possible that some prezygotic traits could be coupled through a shared genetic architecture rather than by direct or indirect selection. Coupling could occur due to pleiotropy, with a change in a single locus producing multiple types of isolation [6].
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