Evolutionary ecology of the social parasite Tamalia inquilinus (Hemiptera: Aphididae)

Most Tamalia aphids induce galls on plants in the family Ericaceae, in western North America.  Tamalia inquilinus must instead invade galls caused by inducers: this socially parasitic behavior is known as inquilinism. The evolutionary origins of inquilinism are incompletely understood.  An earlier analysis of Tamalia mtDNA suggested a single origin of inquilinism in this aphid lineage, and that the social parasites evolved from their hosts in sympatry. To better describe the full evolutionary history of the Tamalia clade, we derived multi-gene phylogenies using data from the nuclear aphid genome and maternally-inherited Buchnera genome.  Our results confirm a single origin of inquiline behavior from a gall-inducing host, possibly in conjunction with a shift in host-plant genus. Our phylogenies and an analysis of molecular variance (AMOVA) show greater topological structure within the inquiline clades and, surprisingly, greater divergence between populations on different host plants than their gall-forming hosts. We explore potential reasons for the striking pattern of ecological decoupling between gall-inducer and host plant, such that inquilines appear to be tracking host plants more closely than they track gall-inducers.