Phylogeny of Rhus gall aphids (Hemiptera: Aphididae) reveals an earlier origin than their primary host plant

Rhus gall aphids (Hemiptera: Aphididae: Eriosomatinae: Fordini)
only use Rhus species (Anacardiaceae) as their primary host plants, and
each aphid specifically lives on only one or two sister host plants with
the same disjunct distribution pattern between Eastern
Asia and Eastern North America. We assembled complete mitochondrial
genomes and universal single-copy nuclear genes for Rhus gall
aphids using a genome skimming method, and the phylogenetic
relationships strongly supported the monophyly of the
Rhus gall aphids and two genera, Floraphis and
Melaphis. However, the relationships among genera are
inconsistent across different datasets. The cpDNA analysis on the host
plant Rhus species strongly supported the Rhus monophyly and
relationship of the Rhus interspecies. Cophylogeny analysis
indicated that the origin of Rhus gall aphids was
earlier than that of their host plants. However, the divergence time and
relationships among some Rhus gall aphid species, particularly
those with later divergence times, were consistent
with the origin of their corresponding primary host
plants. This may suggest that the Rhus gall aphids established
the initial association with the ancestors between
Rhus and the related groups, or acquired current
Rhus hosts through host switching. The divergence time
estimations imply that the separation of North America and
Eurasia in the Laurasia supercontinent and the disappearance of the Bering
Land Bridge, respectively, have played an important role in the divergence
of the eastern North American Melaphis and an East Asian
lineage. Our current results provide new insights into the
coevolution of insects and host plants.