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| Desyopone hereon Boudinot & Perrichot. in Boudinot, Richter, Hammel, ... et Perrichot, 2022. |
Abstract
Fossils are critical for understanding the evolutionary diversification, turnover, and morphological disparification of extant lineages. While fossils cannot be sequenced, phenome-scale data may be generated using micro-computed tomography (µ-CT), thus revealing hidden structures and internal anatomy, when preserved. Here, we adduce the male caste of a new fossil ant species from Miocene Ethiopian amber that resembles members of the Aneuretinae, matching the operational definition of the subfamily. Through the use of synchrotron radiation for µ-CT, we critically test the aneuretine-identity hypothesis. Our results indicate that the new fossils do not belong to the Aneuretinae, but rather the Ponerini (Ponerinae). Informed by recent phylogenomic studies, we were able to place the fossils close to the extant genus Cryptopone based on logical character analysis, with the two uniquely sharing absence of the subpetiolar process among all ponerine genera. Consequently, we: (1) revise the male-based key to the global ant subfamilies; (2) revise the definitions of Aneuretinae, Ponerinae, Platythyreini, and Ponerini; (3) discuss the evolution of ant mandibles; and (4) describe the fossils as †Desyopone hereon gen. et sp. nov. Our study highlights the value of males for ant systematics and the tremendous potential of phenomic imaging technologies for the study of ant evolution. View Full-Text
Keywords: Insecta; ant diversification; poneroid clade; Poneria; Miocene; Ethiopia
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| Photograph of entire amber piece MAIG 6016, with indication of type specimens (labeled H for holotype, P1–P12 for paratypes) of †Desyopone hereon gen. et sp. nov., and with detailed views of seven of them (A–D). (A) paratype 4; (B) holotype; (C) paratypes 1–3; (D) paratypes 5–6. Scale bars: 0.5 mm. |
Genus †Desyopone gen. nov. Boudinot and Perrichot
Type species. †Desyopone hereon sp. nov., by present designation monotypy.
Etymology. The genus name is a portmanteau of the traditional ponerine generic suffix, “-pone”, and the acronym for the Deutsches Elektronen-Synchrotron (DESY), whose storage ring and radiation beamline facilities were used to generate the phenomic data that were crucial for the correct identification of the new taxon.
Diagnosis. †Desyopone has plesiomorphies 1–4 of Ponerinae and is identifiable as Ponerini at minimum due to the vestigial mandibles and infraaxial helcium. †Desyopone and Cryptopone are uniquely identified among all Ponerinae by: (1) subpetiolar process completely absent, with the poststernite low and nearly flat in profile. The new genus differs from the males of all known Cryptopone by the following: (2) head broader than long, excluding the compound eyes (vs. head narrower than long); (3) mandibles elongate (vs. short); (4) mandibles lobate (vs. spiniform); (5) mesospiracular sclerite evidently absent (vs. this sclerite present); (6) meso- and metatibiae with no spur and one spur, respectively (vs. two spurs each); and (7) petiolar peduncle long, about as long as node is tall (vs. peduncle short, considerable shorter than height of node).
†Desyopone hereon sp. nov. Boudinot and Perrichot
Etymology. The specific epithet gratefully recognizes the Helmholtz-Zentrum Hereon, the research center which funds and operates the Imaging Beamline (P05) at DESY, thus making the present work possible.
Type locality. Exact locality unknown in the Bashilo river gorge near Weldiya, Semien Wollo Zone, Amhara Region, Ethiopia.
Type horizon. A fine siltstone/mudstone of Early Miocene age (16–23 Ma).
Diagnosis. †Desyopone hereon is uniquely identifiable among all Ponerinae by the distinctly elongate petiolar peduncle and the enlarged, lobate mandibles.
Conclusions:
Ethiopian amber generally follows the pattern of other Miocene insect deposits, with almost exclusively extant arthropod genera fossilized in inclusions. This holds true for ants, with at least 15 extant genera reported to date [25] (Table 1 therein), while †Desyopone gen. nov. is the first instance of an extinct, new genus that is endemic to Ethiopian amber to date. It is plausible that †Desyopone gen. nov. may ultimately be discovered alive somewhere in Africa, as male ants are yet largely unknown from the continent. A similar case occurred with Gracilidris Wild and Cuezzo, 2006, a dolichoderine first described from a Dominican amber fossil and later found alive in South America [53,54]. Conversely, Ravavy Fisher, 2009 was described from Madagascar before being recently found fossilized in Ethiopian amber.
The present study is a direct instance of genomic–phenomic reciprocal illumination. Moreover, it provides an object lesson in the interpretation of unusual fossils—particularly those with appealing stories, such as the Aneuretinae, for which petiolar tergosternal fusion must be evaluated. Arising from the µ-CT renders of †Desyopone hereon gen. et sp. nov., the global male-based key to ant subfamilies is revised, as well as the definitions of Ponerinae, Platythyreini, Ponerini, and Cryptopone. The new species displays an extreme lost phenotype, albeit one which is biased toward underappreciation as the taxon is known only from males. Systematic reevaluation of male mandibular morphology, however, strongly suggests that the derivation of shovel-shaped mandibles is a synapomorphy of the Poneroformicia clade, with male mandibles themselves representing a largely untapped source of information at the genus level. We anticipate that synchrotron micro-computed tomography and combined-evidence phylogenetics will transform insect systematics.
Brendon E. Boudinot, Adrian K. Richter, Jörg U. Hammel, Jacek Szwedo, Błażej Bojarski and Vincent Perrichot. 2022. Genomic-Phenomic Reciprocal Illumination: Desyopone hereon gen. et sp. nov., an Exceptional Aneuretine-like Fossil Ant from Ethiopian Amber (Hymenoptera: Formicidae: Ponerinae). Insects. 3(9), 796. DOI: 10.3390/insects13090796
https://phys.org/news/2022-09-scientists-extinct-ant-species-encased.html
Simple Summary: We describe a new species of extinct ants from Miocene-aged Ethiopian amber, based on males that resemble species of the relictual lineage Aneuretinae, but which effectively belong to the Ponerinae, as revealed by advanced 3D-imaging technology (synchrotron radiation micro-computed tomography, SR-µ-CT). We subsequently propose a revision of ant classification at the subfamily level. We also recognize that the new species belongs to a new genus based on recent phylogenomic results that have clarified the generic boundaries of Ponerini ants. Our work, therefore, represents an example of reciprocal illumination between phenomic and genomic data.
