| Summary: | Mesynodites is the largest genus within the exclusively inquilinous (social insect-associated) histerid beetle subfamily Hetaeriinae (Insecta: Coleoptera: Histeridae). The 44 described species are systematically revised, and new taxa are described based on newly discovered species and the results of a cladistic analysis. The work was based on available type specimens representing 42 species and approximately 2500 specimens of non-type material. Phylogenetic hypotheses were based on maximum parsimony analysis of 150 morphological characters derived from a selection of Mesynodites species and representatives of related genera. This analysis confirmed that, in its current concept, Mesynodites is not a monophyletic taxon. Species included currently in Mesynodites were scattered among 11 distinct lineages. As a result, in the revised sense, Mesynodites includes only nine species, two of which are of uncertain affinities (type specimens of these species were not located).
Revision of Mesynodites species in the context of the phylogenetic analysis allowed numerous taxonomic changes to the Hetaeriinae. Presentation of those changes in this dissertation does not constitute formal publication. The following taxonomic changes are introduced: two new tribes are described and all genera of Hetaeriinae, excluding 12 genera of doubtful affinities, received tribal assignments; eight new genera and three new species are described; 37 new combinations and five new synonimities are established.
The phylogenetic hypothesis of relationships within Mesynodites and allies (tribe Nymphisterini) provided some insight into evolution of host use in the lineage. This group evolved with army ants (Hymenoptera: Ecitoninae) and are known to occur with several species within the genera Eciton, Labidus, Neivamyrmex and Nomamyrmex. The ancestral host genus washypothesized to be either Eciton or Labidus. Contrary to previous opinions, species in several genera of Nymphysterini live with multiple host ant genera. Two separate host switches
from army ants (Nomamyrmex and possibly Neivamyrmex) to leaf cutter ants Atta are hypothesized for species in Mutodites and Mesynodites. Analysis of host use and speciation revealed a trend of 1.5-2.5 times fewer species per strictly specialized (single host genus) guest genus, and this trend was consistent across different levels of analysis (Nymphysterini, all ecitophiles and all Hetaeriinae).
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