Next-generation morphological character discovery and evaluation: an X-ray micro-CT enhanced revision of the ant genus Zasphinctus Wheeler (Hymenoptera, Formicidae, Dorylinae) in the Afrotropics

Abstract

New technologies for imaging and analysis of morphological characters offer opportunities to enhance revisionary taxonomy and better integrate it with the rest of biology. In this study, we revise the Afrotropical fauna of the ant genus Zasphinctus Wheeler, and use high-resolution X-ray microtomography (micro-CT) to analyse a number of morphological characters of taxonomic and biological interest. We recognise and describe three new species: Z. obamai sp. n., Z. sarowiwai sp. n., and Z. wilsoni sp. n. The species delimitations are based on the morphological examination of all physical specimens in combination with 3D scans and volume reconstructions. Based on this approach, we present a new taxonomic discrimination system for the regional fauna that consists of a combination of easily observable morphological characters visible at magnifications of around 80–100 ×, less observable characters that require higher magnifications, as well as characters made visible through virtual dissections that would otherwise require destructive treatment. Zasphinctus are rarely collected ants and the material available to us is comparatively scarce. Consequently, we explore the use of micro-CT as a non-invasive tool for the virtual examination, manipulation, and dissection of such rare material. Furthermore, we delineate the treated species by providing a diagnostic character matrix illustrated by numerous images and supplement that with additional evidence in the form of stacked montage images, 3D PDFs and 3D rotation videos of scans of major body parts and full body (in total we provide 16 stacked montage photographs, 116 images of 3D reconstructions, 15 3D rotation videos, and 13 3D PDFs). In addition to the comparative morphology analyses used for species delimitations, we also apply micro-CT data to examine certain traits, such as mouthparts, cuticle thickness, and thoracic and abdominal muscles in order to assess their taxonomic usefulness or gain insights into the natural history of the genus. The complete datasets comprising the raw micro-CT data, 3D PDFs, 3D rotation videos, still images of 3D models, and coloured montage photos have been made available online as cybertypes (Dryad, http://dx.doi.org/10.5061/dryad.4s3v1).

Systematics of the ant genus Proceratium Roger (Hymenoptera, Formicidae, Proceratiinae) in China – with descriptions of three new species based on micro-CT enhanced next-generation-morphology

“…We also give species accounts for all other valid species and add a locality record for Proceratium longigaster Karavaiev, 1935. Like in previous studies (Fischer et al 2016, Sarnat et al 2016, Agavekar et al 2017, Hita Garcia et al 2017a, 2017b), we continue using and exploring microtomography for ant taxonomy. In order to visually enhance the taxonomic descriptions, we provide still images and 3D videos based on surface volume renderings of micro-CT scans from all Chinese species (except for P. longmenense Xu, 2006).…”

“…One problem encountered by Hita Garcia et al (2017b) was the poor recovery of pilosity in the 3D reconstructions due to insufficient voxel resolution, which was resolved in Hita Garcia et al (2017a) by scanning single body parts at higher resolutions. Nevertheless, in this study, we aimed to turn this handicap into an advantage.…”

“…Post-processing of mesh data in order to generate clean surfaces was done with Meshlab (version 1.3.3). The methodology for the virtual examinations of 3D surface models, generation of 3D rotation videos, and virtual dissections follow Hita Garcia et al (2017a). For more details on micro-CT scanning and post-processing workflow pipeline, we refer to the exhaustive descriptions in Hita Garcia et al (2017a, 2017b).…”

“…The virtual nature of such reconstructions enables non-destructive and comprehensive 3D analyses of anatomy and morphology (Faulwetter et al 2013, Friedrich et al 2014). Another crucial benefit of micro-CT is its application for virtual dissections and identification of new diagnostic characters (Deans et al 2012), which has been successfully applied for lepidopterans (Simonsen and Kitching 2014), mayflies (Sartori et al 2016), and recently ants (Hita Garcia et al 2017a). …”

“…In the last years, this situation is changing and micro-CT has become a powerful tool to visually enhance and support diagnostic species delimitations, from single species descriptions to revisions. While initially used for polychaetes (Faulwetter et al 2013), myriapods (Stoev et al 2013, Akkari et al 2015), spiders (Michalik and Ramírez 2013), earthworms (Fernández et al 2014), and flatworms (Carbayo and Lenihan 2016, Carbayo et al 2016), micro-CT has evolved into a cutting-edge tool increasingly applied for ant taxonomy (Csősz 2012, Fischer et al 2016, Sarnat et al 2016, Agavekar et al 2017, Hita Garcia et al 2017a, 2017b). A detailed and critical assessment of the technology and its applications for ant taxonomy was provided by Hita Garcia et al (2017b).…”