Phylogeny and Biogeography of Dolichoderine Ants: Effects of Data Partitioning and Relict Taxa on Historical Inference

Ants (Hymenoptera: Formicidae) are conspicuous organisms in most terrestrial ecosystems, often attaining high levels of abundance and diversity. In this study, we investigate the evolutionary history of a major clade of ants, the subfamily Dolichoderinae, whose species frequently achieve ecological dominance in ant communities. This group has also produced some of the world's most successful invasive ants. We use an extensive molecular data set ( approximately 9 kb of sequence data from 10 nuclear genes, covering 48 dolichoderine species and 6 outgroup taxa) to infer the phylogenetic relationships, divergence dates, and biogeographic history of these ants. We evaluate the effects of data partitioning and outgroup composition on phylogenetic inference by estimating relationships under a series of increasingly partitioned data sets and by running analyses both with and without Aneuretus simoni, a rare and localized species that is the nearest living relative of Dolichoderinae. We also examine the effects of excluding 2 data partitions with significant base composition heterogeneity. Our results reveal 4 well-supported and mutually exclusive clades of dolichoderines, corresponding to 4 newly defined tribes: Bothriomyrmecini (B), Dolichoderini (D), Leptomyrmecini (L), and Tapinomini (T). All Bayesian and likelihood analyses yield the same unrooted (ingroup-only) topology, ((D,L),(B,T)), with the outgroups attaching either on the Dolichoderini branch or on the Tapinomini branch. Placement of the root is highly sensitive to choice of model partition and to inclusion/exclusion of Aneuretus. Bayes' factors strongly favor the more partitioned models, and in these Tapinomini is recovered as sister to the remaining dolichoderines, but only if Aneuretus is included. Exclusion of Aneuretus precludes recovery of this topology in all but the most highly partitioned Bayesian analyses and then only with nonsignificant support, underscoring the importance of relict, taxonomically isolated taxa for phylogenetic inference. Removal of 2 partitions with heterogeneous base composition also markedly increases support for placement of the root on the Tapinomini branch. Our divergence date estimates and biogeographic analyses indicate that crown-group dolichoderines arose about 65 million years ago (Ma), although this was preceded by a substantial period (30 million years) of stem group evolution. The 4 extant tribes are estimated to have crown-group origins in the late Paleocene or Eocene (40-60 Ma). Tapinomini and Bothriomyrmecini originated in the Paleotropics and subsequently dispersed to other biogeographic regions. Crown-group Leptomyrmecini arose and diversified in the Neotropics, but they also gave rise to one clade that colonized Australia about 30 Ma and subsequently experienced a massive radiation on that continent. This event occurred later than the diversification of dolichoderines in the northern hemisphere, so that by the time dolichoderines came to dominate the Australian fauna they had already declined in abundance in the Holarctic region.