Background: On the basis of molecular dating, Pleistocene glaciations have been

proposed as the major driving force of biota speciation in the Palearctic and the

pre-Quaternary origin of Amazonian taxa. However, the major driving factors in East

Asia remain unclear. All 16 saturniine species inhabiting Taiwan with congeners of

populations, subspecies, or species in East Asia constitute research objects for

addressing the mode of speciation because of the repeated formation and

disappearance of a landbridge from the Asian mainland to Taiwan during glacial

cycles.

Methods: The genetic divergences of mitochondrial cytochrome c oxidase subunit I

(COI) and 16S rDNA and the nuclear 28S rDNA of the saturniine species from

Taiwan and the Asian mainland were assessed to determine the monophyly of each

genus and species of Saturniinae. Moreover, 519 saturniine COI sequences of 114

taxa from adjacent East and Southeast Asian populations and closely related species

were retrieved from GenBank and analyzed. The differentiation timing and possible

origination of the insular saturniines were elucidated based on phylogenetic

relationships, haplotype networks, and lineage calibrations.

Results: Approximately 90% of intraspecific COI divergence was <2%; all

divergences exceeding 2% originated from comparisons between allopatric

populations or subspecies. Relationship analyses revealed that multiple introductions

likely occurred in insular saturniines and that some East Asian saturniines were

paraphyletic as deduced by analyzing endemic insular species. Calibration dating

revealed that Taiwanese endemic saturniines split from sibling Asian species

0.2–2.7 million years ago (Mya), whereas subspecific-level and population-level

splitting events occurred 0.1–1.7 Mya and 0.2–1.2 Mya, respectively. Moreover,

phylogenetic patterns combined with geographical distributions revealed that

hill-distributed Taiwanese saturniines are closely related to those from southern

China and Southeast Asia, whereas saturniines inhabiting altitudes higher than

1,500 m in Taiwan have siblings distributed in temperate Northeast Asia.

Discussion: The Global DNA Barcoding Initiative was successfully applied to study

the population genetic structure in species. Most Formosan saturniines are

distinct and monophyletic, reflecting the vicariant barrier of the Taiwan Strait;

Pleistocene glacial cycles provided opportunities for insular saturniines to experience

repeated isolation from and secondary contact with the continental mainland. Each

insular saturniine may have evolved with a unique differentiation timing pattern

that possibly emerged in the Early, Middle, or Late Pleistocene with these patterns

differing from the consistent pattern that occurred in the temperate Palearctic and

tropical Amazonian regions. Moreover, multiple migrations or artificial genetic

admixtures may have also occurred, as suggested by the coexistence of two divergent

lineages in a few Taiwanese saturniines.