Dissecting the species groups of Paussus (Carabidae: Paussinae): unraveling morphological convergence associated with myrmecophilous life histories

Among the charismatic, flanged bombardier beetles (Carabidae: Paussinae), the genus Paussus is most diverse, with ~340 described species distributed in the tropical regions of the Old World. The species diversity within this genus is reflected in an astounding breadth of morphological diversity.

Phylogenetic relationships within Paussus have been obscured by extreme anatomical adaptations and convergences resulting from myrmecophilous life styles. Previous attempts to delineate subgenera and species groups have placed emphasis on phylogenetically labile morphological traits, most of which are likely to be under strong selective pressure by host ants, thereby leading to unnatural groupings.

The objectives of this research are to: (1) infer the phylogenetic history of Paussus, (2) delineate species group clades within Paussus, (3) identify morphological synapomorphies for Paussus species groups, and (4) investigate the evolution and convergence of select anatomical traits in light of the phylogenetic and biogeographic history of Paussus.

We attempt to accomplish these objectives by conducting an in-depth anatomical study of Paussus and constructing a matrix for phylogenetic inference based on adult morphology. Using mixed-model Bayesian inference, we analyze the morphological data alone and in combination with a complimentary multi-gene data set for Paussus (Moore, in prep.).

The resulting phylogenetic hypotheses discussed provide a framework for investigating the evolutionary history of Paussus. We recover three well-supported monophyletic groups within Paussus, each supported by multiple morphological synapomorphies. Many morphological features used historically to delineate Paussus subgroups are shown to be highly convergent, likely the result of strong selective pressure by their host ants.