Community Sampling and Integrative Taxonomy Reveal New Species and Host Specificity in the Army Ant-Associated Beetle Genus Tetradonia (Coleoptera, Staphylinidae, Aleocharinae).

Army ant colonies host a diverse community of arthropod symbionts. Among the best-studied symbiont communities are those of Neotropical army ants of the genus Eciton. It is clear, however, that even in these comparatively well studied systems, a large proportion of symbiont biodiversity remains unknown. Even more striking is our lack of knowledge regarding the nature and specificity of these host-symbiont interactions. Here we surveyed the diversity and host specificity of rove beetles of the genus Tetradonia Wasmann, 1894 (Staphylinidae: Aleocharinae). Systematic community sampling of 58 colonies of the six local Eciton species at La Selva Biological Station, Costa Rica, combined with an integrative taxonomic approach, allowed us to uncover species diversity, host specificity, and co-occurrence patterns of symbionts in unprecedented detail. We used an integrative taxonomic approach combining morphological and genetic analyses, to delineate species boundaries. Mitochondrial DNA barcodes were analyzed for 362 Tetradonia specimens, and additional nuclear markers for a subset of 88 specimens. All analyses supported the presence of five Tetradonia species, including two species new to science. Host specificity is highly variable across species, ranging from generalists such as T. laticeps, which parasitizes all six local Eciton species, to specialists such as T. lizonae, which primarily parasitizes a single species, E. hamatum. Here we provide a dichotomous key along with diagnostic molecular characters for identification of Tetradonia species at La Selva Biological Station. By reliably assessing biodiversity and providing tools for species identification, we hope to set the baseline for future studies of the ecological and evolutionary dynamics in these species-rich host-symbiont networks.

A reappraisal of the diversity and class distribution of aspartate transcarbamoylases in gram-negative bacteria.

Recently, the subunit composition of class A aspartate transcarbamoylases (ATCases) in fluorescent pseudomonads has been clarified. We present evidence that distribution of this type of ATCase may be more widespread than at first suspected. Bacterial ATCases exist in three forms: class A (molecular mass approximately 450-500 kDA); class B, typified by Escherichia coli ATCase (approximately 300 kDa); and class C, typified by Bacillus subtilis ATCase (approximately 100 kDa). Using gradient gel electrophoresis with activity-staining to scan bacterial sonicates, we report the existence of six more class ATCases. We have purified one of these, Acinetobacter calcoaceticus ATACase, and found its subunit composition to be similar to that of the pseudomonad ATCases. Two of these ATCases come from bacteria outside the gamma-subgroup of the Proteobacteria, one from the alpha-subgroup and one from Deinococcus radiophilus, a species phylogenetically remote from the Proteobacteria. Unexpectedly, three bacterial species, closely related to the fluorescent pseudomonads and acinetobacters, have ATCases of 100 kDa (class C). One of these, Stenotrophomonas (formerly Xanthomonas) maltophilia has been purified and found to be a homotrimer of 35 kDa polypeptide chains. We believe this is the first time that class C ATCases have been reported in Gram-negative bacteria. A distinctive cluster in the gamma-3 subgroup of the Proteobacteria is formed by the enteric bacteria and their relatives. So far only class B ATCases have been reported in this group. The evolutionary implications of these findings are discussed.