Proceratium zhaoi Xu, 2000

Staab, Michael, Garcia, Francisco Hita, Liu, Cong, Xu, Zheng-Hui & Economo, Evan P., 2018, 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, ZooKeys 770, pp. 137-192 : 137

Proceratium zhaoi Xu, 2000 Figs 4A, 15, 16, 17, 25

Proceratium zhaoi Xu, 2000: 435 (w.q.), China

Proceratium nujiangense Xu, 2006: 153 (w.q.), China, syn. n.

Type material.

Of P. zhaoi : Holotype. Pinned worker from CHINA, Yunnan Province, Menghai County, Meng’a Town, Papo Village, 1280 m asl, deciduous broadleaved forest, soil sample, 10-IX-1997, leg. Zheng-Hui Xu, No. A97-2338 (in SWFU) [examined].

Paratypes. Six pinned workers and 24 alate females; one worker with same data as holotype; all other paratypes with same data as holotype but No. A97-2380 (CASENT0235334 in CASC; CASENT0790671 and all other paratypes in SWFU) [all examined].

Of P. nujiangense : Holotype. Pinned worker from CHINA, Yunnan Province, Baoshan City, Lujiang Town, Bawan, 1500 m asl, Pinus yunnanensis forest on east slope of Nujiang River Valley, 11-VIII-1998, leg. Qizhen Long, label “A98-1964” (in SWFU) [examined].

Paratypes. Seven pinned workers and 10 queens with same data as holotype but No. A98-1995, No. A98-1997, No. A98-2010, No. A98-2016, No. A98-2029 (CASENT0790672 and all other paratypes in SWFU) [all examined].

Virtual dataset.

Volumetric raw data (in DICOM format), 3D rotation videos (in.mp4 format, see Suppl. material 6: Video 4 for P. zhaoi and Suppl. material 7: Video 5 for P. nujiangense ), still images of surface volume rendering, and 3D surfaces (in PLY format) of a paratype of P. zhaoi (CASENT07900671) and a paratype of P. nujiangense (CASENT0790672) in addition to montage photos illustrating head in full-face view, profile and dorsal views of the body. The data is deposited at Dryad ( Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p) and can be freely accessed as virtual representations of the species. In addition to the data at Dryad, we also provide freely accessible 3D surface models at Sketchfab (https://skfb.ly/6txOT and https://skfb.ly/6txOL).

Diagnosis.

Proceratium zhaoi differs from the other members of the P. itoi clade by the following character combination: small species (TL 2.0-2.8, WL 0.66-0.80; measurements and indices use data from the original descriptions); of head weakly convex, broadest at level of eyes and gently narrowing anteriorly and posteriorly, posterior head margin weakly concave to almost straight; frontal carinae developed, their lateral lamellae relatively narrow, not extending over antennal insertions; posterodorsal corners of propodeum bluntly angled; posterior face of petiolar node, in profile, shorter and steeper than anterior face, dorsum of node broadly rounded, petiole as long as broad or broader than long (DPeI 98-110), subpetiolar process developed, relatively variable, varying in size and shape (from rectangular to triangular to acutely toothed); only dense pubescence, no erect hairs on dorsum of body, head, and scapes.

Distribution and ecology.

This species is only known from two locations at mid elevation in forests of southern and western Yunnan Province. The original description reported 45 workers in the type colony ( Xu 2000) and no other data on natural history have been published. However, the relatively short legs suggest a purely hypogeic life style, which conforms to the fact that specimens were extracted from soil samples.

Taxonomic notes.

Even though at the beginning of this study we treated P. nujiangense and P. zhaoi as distinct species, thorough examinations combining traditional microscopy with micro-CT scans proved that there are no morphological characters separating them. The virtual comparisons of type specimens of both taxa showed that there are no morphological differences, a fact that is not easy to observe by comparing physical specimens. The types are hairy, dirty, and mounted in ways that hide most important characters, as it is typical for most Proceratium specimens. Furthermore, the main character used by Xu (2006) to separate the species was the subpetiolar process, which has been used for species diagnostics in previous studies ( Baroni Urbani and de Andrade 2003, Hita Garcia et al. 2014, 2015). However, these works either had very little material for the assessment of intraspecific variation and/or treated different clades of Proceratium . Our study shows that the subpetiolar process is extremely variable within the P. itoi clade and refrain from using it for species delimitations. As a matter of fact, the variation of the subpetiolar process was already noted in the description of P. zhaoi ( Xu 2000). Reexamination of all type specimens of both species also revealed a comparatively high degree of variation and overlap in the form of the posterodorsal corner of the propodeum and the width of the propodeal node. In addition, the morphometric ranges of P. nujiangense and P. zhaoi overlap and form a continuum, and there are no significant differences in proportions since all indices are identical. Considering these similarities in light of the newly available images and micro-CT data, we propose treating P. nujiangense as a junior synonym of P. zhaoi .

This species was not mentioned in the revision of Baroni Urbani and de Andrade (2003), potentially because the authors were not aware of its description shortly before the completion of their monograph. Despite some size variation (TL 2.0-2.8), the relative body proportions of P. zhaoi are constant (CI 84-90, SI 61-66). Proceratium zhaoi is the smallest (WL 0.66-0.80) member of the P. itoi clade. It can be distinguished from all other P. itoi clade species (except for P. williamsi ) by the absence of erect hairs that protrude through the dense pubescence on the dorsal body surface. Proceratium williamsi also lacks hairs on the dorsal body surface, but is larger (WL 0.80-0.92), has stronger developed frontal carinae and relatively more slender and longer legs. The relatively weakly developed frontal carinae and the short legs (MFeI <80, MTiI <65, MBaI <40) make P. zhaoi also unique among the Chinese P. itoi clade species.