Evolutionary history, novel lineages, and symbiont coevolution in the ant tribe Camponotini (Hymenoptera: Formicidae)

Many insect groups have acquired obligate microbial symbionts, and the
resulting associations can have important ecological and evolutionary
consequences. A notable example among ants is the species-rich tribe
Camponotini, whose members derive nutritional benefits from a vertically
inherited, bacterial endosymbiont Blochmannia. We generate ultraconserved
element (UCE) phylogenomic data for 220 ingroup and 5 outgroup taxa to
reconstruct a detailed evolutionary history of the Camponotini, including
inference of divergence times and dispersal events. Under multiple modes
of analysis, including both concatenation and species-tree approaches, we
recover a well-supported backbone phylogeny comprising eight lineages:
three large genera (Camponotus, Colobopsis, Polyrhachis) and several
smaller genera or clusters of genera. Three novel lineages are uncovered
that cannot be placed in any existing genus: Lathidris gen. n., from the
mountains of Mesoamerica; Retalimyrma gen. n., from the Indian Himalayas;
and Uwari gen. n., from eastern Asia. The species in these new genera were
described and placed erroneously in Camponotus. The tribe Camponotini is
estimated to have a crown origin in the Eocene (median age 38.4 Ma), with
successively younger crown ages for Colobopsis (22.5 Ma), Camponotus (18.6
Ma), and Polyrhachis (18.5 Ma). We infer an Australasian or Indomalayan
origin for the tribe, with multiple dispersal events to the Afrotropics,
Palearctic region, and New World. Phylogenetic analysis of selected
Blochmannia genes from a subset of 97 camponotine taxa yields results that
are largely congruent with the ant host phylogeny, at least for
well-supported nodes, but we find evidence that Blochmannia from some old
lineages—especially Lathidris—may have discordant histories, suggesting
possible lability of this symbiosis in the early evolution of camponotine
ants.