Allochronic isolation and incipient hybrid speciation in tiger swallowtail butterflies

Abstract

Hybridization leading to reproductively isolated, novel genotypes is poorly understood as a means of speciation and few empirical examples have been studied. In 1999, a previously non-existent delayed flight of what appeared to be the Canadian tiger swallowtail butterfly, Papilio canadensis, was observed in the Battenkill River Valley, USA. Allozyme frequencies and morphology suggest that this delayed flight was the product of hybridization between Papilio canadensis and its sibling species Papilio glaucus. The mitochondrial DNA (mtDNA) restriction fragment length polymorphisms presented here indicate that only P. canadensis-like mtDNA occurs in this population, suggesting that introgression likely occurred from hybrid males mating with P. canadensis females. Preliminary studies of this population indicated that delayed post-diapause pupal emergence in this hybrid genotype was the root cause behind the observed delayed flight, which suggests a potential empirical example of a mechanism leading to reproductive isolation. Here we provide further evidence of the role of adult pupal emergence as a reproductive barrier likely leading to reproductive isolation. In particular, we present results from pupal emergence studies using four different spring and two different winter temperature treatments. The results indicate a clear separation of adult emergences between the hybrid population and both parental species. However, our results indicate that exceptionally hot springs are likely to lead to greater potential for overlap between the local parental species, P. canadensis, and this delayed population with hybrid origins. Conversely, our results also show that warmer winters are likely to increase the temporal separation of the hybrid population and the parental species. Finally, we report recently collected evidence that this hybrid population remains morphologically distinct.

Sympatric, temporally isolated populations of the pine white butterfly Neophasia menapia, are morphologically and genetically differentiated

“…We determine the biogeographic origin of populations at the sympatric sites is likely to have come from within the Coast Range, not from the Sierra Nevada. This case, along with other recent work on temporal isolation [1, 9–11, 13, 55, 56] demonstrates that temporal isolation may occur more frequently than previously thought and warrants further research into the underlying mechanism of this process of reproductive isolation.…”

“…The term allochronic speciation was developed to describe cases in which the initial stages of speciation are set in motion by a change in phenology [1, 7]. Once thought to be a relatively rare form of reproductive isolation, in recent years there have been examples of allochronic and temporal isolation across many diverse taxa; including insects [8–11], plants [12], birds [13], and corals [14], indicating that temporal differentiation is a potentially important isolating mechanism.…”

Assortative mating between two sympatric closely-related specialists: inferred from molecular phylogenetic analysis and behavioral data

“…Considering the incomplete post-mating reproductive isolation181920, we suggest near perfect assortative mating has evolved. Differing from many studies in which allochronic factors play an important role in reproductive isolation and speciation41, allochronic isolation contribute little in the present system. As many other herbivorous specialists, Altica flea beetles exhibit high host fidelity19, and the spatial segregation of the host plant species reduces encounters between the two beetles.…”

Recent Speciation in Three Closely Related Sympatric Specialists: Inferences Using Multi-Locus Sequence, Post-Mating Isolation and Endosymbiont Data

“…In some butterflies ( Papilio ), the host race formation is the result of, not the cause of genetic and ecological divergence [67], and the divergence achieved by temporal isolation but not feeding/habitat specialization [68]. The parental species of Papilio are also not isolated by pre-mating mate-preference barriers [69] nor by post-mating egg viability.…”