Historical biogeography of Eastern Asian-Eastern North American disjunct Melaphidina aphids (Hemiptera: Aphididae: Eriosomatinae) on Rhus hosts (Anacardiaceae).

Intercontinental biotic disjunctions have been documented and analyzed in numerous Holarctic taxa. Patterns previously synthesized for animals compared to plants suggest that the timing of animal disjunctions are mostly Early Tertiary and were generated by migration and vicariance events occurring in the North Atlantic, while plant disjunctions are mostly Mid-Late Tertiary and imply migration and vicariance over Beringia. Melaphidina aphids (Hemiptera: Aphididae: Fordini) exhibit host-alternating life cycles comprising an obligate seasonal shift between Rhus subgenus Rhus species (Anacardiaceae) and mosses (Bryophyta). Similar to their Rhus hosts, melaphidines are distributed disjunctly between Eastern Asia and Eastern North America. We examined evolutionary relationships within Melaphidina to determine the position of the North American lineage, date its divergence from Asian relatives, and compare these results to a previous historical biogeographic study of Rhus. We sampled nine species and three subspecies representing all six genera of Melaphidina. Data included sequences of mitochondrial cytochrome c oxidase subunits I and II+leucine tRNA, cytochrome b, and nuclear elongation factor 1α genes. Phylogenetic analyses (Bayesian, maximum-likelihood, parsimony) of the combined data (3282 bp) supported the monophyly of all genera except Nurudea and Schlechtendalia, due to the position of N. ibofushi. While the exact position of the North American Melaphis was not well resolved, there was high support for a derived position within Asian taxa. The divergence of Melaphis from Asian relatives centered on the Eocene-Oligocene boundary (~33-35Ma), which coincides with closure of Beringian Land Bridge I. This also corresponded to the Asian-North American disjunction previously estimated for subgenus Rhus spp. We suggest the late-Eocene Bering Land Bridge as the most likely migration route for Melaphis ancestors, as was also hypothesized for North American Rhus ancestors. Results for the Melaphidina disjunction depart from the modal pattern in animal lineages, and present a case where insect and host-plant taxa apparently responded similarly to Tertiary climate change.