Natural history of the social millipede Brachycybe lecontii Wood, 1864

The Chemistry of the Defensive Secretions of Three Species of Millipedes in the Genus Brachycybe

Millipedes have long been known to produce a diverse array of chemical defense agents that deter predation. These compounds, or their precursors, are stored in high concentration within glands (ozadenes) and are released upon disturbance. The subterclass Colobognatha contains four orders of millipedes, all of which are known to produce terpenoid alkaloids-spare the Siphonophorida that produce terpenes. Although these compounds represent some of the most structurally-intriguing millipede-derived natural products, they are the least studied class of millipede defensive secretions. Here, we describe the chemistry of millipede defensive secretions from three species of Brachycybe: Brachycybe producta, Brachycybe petasata, and Brachycybe rosea. Chemical investigations using mass spectrometry-based metabolomics, chemical synthesis, and 2D NMR led to the identification of five alkaloids, three of which are new to the literature. All identified compounds are monoterpene alkaloids with the new compounds representing indolizidine (i.e. hydrogosodesmine) and quinolizidine alkaloids (i.e. homogosodesmine and homo-hydrogosodesmine). The chemical diversity of these compounds tracks the known species phylogeny of this genus, rather than the geographical proximity of the species. The indolizidines and quinolizidines are produced by non-sympatric sister species, B. producta and B. petasata, while deoxybuzonamine is produced by another set of non-sympatric sister species, B. rosea and Brachycybe lecontii. The fidelity between the chemical diversity and phylogeny strongly suggests that millipedes generate these complex defensive agents de novo and begins to provide insights into the evolution of their biochemical pathways.

A new species of Illacme from southern California (Siphonophorida, Siphonorhinidae)

The millipede fauna inhabiting deep soil are poorly known. They are small and threadlike, slow moving, lacking pigmentation, and rarely encountered due to their obscure underground way of life. One family, the Siphonorhinidae, encompasses four genera and 12 species in a fragmentary distribution in California, southern Africa, Madagascar, the Malay Archipelago, and Indo-Burma. The family is represented in the Western Hemisphere by a single genus, Illacme Cook & Loomis, 1928 from California, with its closest known relative, Nematozoniumfilum Verhoeff, 1939, from southern Africa. A new species of this family is documented from soil microhabitats in the Los Angeles metropolitan area, Illacmesocal Marek & Shear, sp. nov. Based on this discovery and the recent documentation of other endogean millipede species, we show that these grossly understudied subterranean fauna represent the next frontier of discovery. However, they are threatened by encroaching human settlement and habitat loss, and conservation of this species and other subterranean fauna is of high importance.

Deoxybuzonamine Isomers from the Millipede Brachycybe lecontii (Platydesmida: Andrognathidae)

Millipedes (Diplopoda) are well known for their toxic or repellent defensive secretions. Here, we describe (6aR,10aS,10bR)-8,8-dimethyldodecahydropyrrolo[2,1-a]isoquinoline [trans-anti-trans-deoxybuzonamine (1a)] and (rel-6aR,10aR,10bR)-8,8-dimethyldodecahydropyrrolo[2,1-a]isoquinoline [trans-syn-cis-deoxybuzonamine (1b)], two isomers of deoxybuzonamine found in the chemical defense secretions of the millipede Brachycybe lecontii Wood (Colobognatha, Platydesmida, Andrognathidae). The carbon-nitrogen skeleton of these compounds was determined from their MS and GC-FTIR spectra obtained from the MeOH extract of whole millipedes, along with a subsequent selective synthesis. Their structures were established from their 1D (¹H, ¹³C) and 2D NMR (COSY, NOESY, multiplicity-edited HSQC, HSQC-TOCSY, HMBC) spectra. Additionally, computational chemistry (DFT and DP4) was used to identify the relative configurations of 1a and 1b by comparing predicted ¹³C data to their experimental values, and the absolute configuration of 1a was determined by comparing its experimental specific rotation with that of the computationally calculated value. This is the first report of dodecahydropyrrolo[2,1-a]isoquinoline alkaloids from a platydesmidan millipede.

A previously unknown feeding mode in millipedes and the convergence of fluid feeding across arthropods

We report fluid feeding with a sucking pump in the arthropod class Diplopoda, using a combination of synchrotron tomography, histology, electron microscopy, and three-dimensional reconstructions. Within the head of nine species of the enigmatic Colobognatha, we found a pumping chamber, which acts as positive displacement pump and is notably similar to that of insects, showing even fine structural convergences. The sucking pump of these millipedes works together with protractible mouthparts and externally secreted saliva for the acquisition of liquid food. Fluid feeding is one of the great evolutionary innovations of terrestrial arthropods, and our study suggests that it evolved with similar biomechanical solutions convergent across all major arthropod taxa. While fluid-feeding insects are megadiverse today, it remains unclear why other lineages, such as Colobognatha, are comparably species poor.

Gosodesmine, a 7-Substituted Hexahydroindolizine from the Millipede Gosodesmus claremontus

Millipedes (Diplopoda) are well known for their toxic or repellent defensive secretions. Here we describe gosodesmine (1), 7-(4-methylpent-3-en-1-yl)-1,2,3,5,8,8a-hexahydroindolizine, a unique alkaloid with some terpene character found in the chemical defense secretions of the millipede Gosodesmus claremontus Chamberlin (Colobognatha, Platydesmida, Andrognathidae). The structure of 1 was suggested by its mass spectra and GC-FTIR spectra and established from its ¹H, ¹³C, and 2D NMR spectra and 1D NOE studies. The 7-substituted indolizidine carbon skeleton of 1 was confirmed by unambiguous synthesis. This is the first report of an alkaloid from a platydesmid millipede and the first report of a 7-substituted indolizidine from an arthropod.