A new genus and species of Staphylininae rove beetle from the Peruvian Amazon (Coleoptera, Staphylinidae)

Abstract A new monotypic genus of Staphylininae Latreille, 1802 tribe incertae sedis is proposed based on Amazonothops aslakigen. et sp. nov. from the Peruvian Amazon. Descriptions and illustrations of the new genus and species are provided. Its systematic placement and phylogenetic significance are discussed.


Introduction
During a field trip to the Amazonian region of Peru, members of the Natural History Museum of Denmark Coleoptera section collected several conspecific specimens of a small rove beetle which strongly resembled the widespread, polyphyletic genus Heterothops Stephens, 1829 from the tribe Amblyopinini (Jenkins Shaw et al. 2019). One of these specimens was included in the molecular phylogenetic analysis of Jenkins Shaw et al. (2019). Whilst that study primarily sought to investigate the phylogeny of the tribe Amblyopinini, it also included a broad sample of representative Staphylininae and other subfamilies of Staphylinidae as outgroups. The results of that phylogeny recovered the Amazonian taxon as sister to the tribes Tanygnathinini and Hyptiomini with strong support, far away from Heterothops and even Amblyopinini as a whole (Fig. 1). Further morphological study revealed numerous unusual characters that confirmed it indeed did not belong to the genus Heterothops or even the tribe Amblyopinini. At the same, it was morphologically distinct from either Tanygnathinini or Hyptiomini. Without hesitation we describe Amazonothops aslaki gen. et sp. nov. Even though we place this new genus as incertae sedis in the subfamily Staphylininae pending further inquiry, we provide comparisons and discussion to explain why Amazonothops is an important discovery for understanding evolution of the morphologically heterogeneous and still rather enigmatic clade it belongs to.

Material and methods
Specimens studied are deposited in the following institutions: One specimen was prepared for scanning electron microscopy (SEM) by initial immersion in soapy water, followed by 1 hour in 10% KOH, resting overnight in 70% alcohol, then successive immersion in 96% alcohol for 15 minutes, in 99.9% alcohol for 15 minutes and in acetone for 15 minutes. SEM photographs were taken using a JEOL JSM-6335F SEM at the NHMD. One specimen was slide mounted using the method described in Hanley and Ashe (2003): slide photographs were taken using a Canon EOS 6D DSLR (Canon Inc.) digital camera mounted on a Zeiss Axioskop 50 via a LM Digital SLR Universal Adapter. Images were captured from multiple focal planes with the help of Canon EOS utility 3.4.30.0 software (Canon Inc.), combined with Zerene Stacker (Zerene Systems LLC, Richland, USA) software and edited with Adobe Photoshop CS6 and Adobe Illustrator CS6 (Adobe Systems, San Jose, CA, U.S.A) afterwards. The map in Fig. 6 was generated using SimpleMappr (Shorthouse 2010). Holotype or paratype labels have been added to all type specimens, respectively. Measurements were taken using ImageJ and calibrated based on the scale bar in the images. Measurements were based on a single specimen as all individuals studied exhibited very little or no variation in size or proportions.

NHMD
The following measurements were taken (all in mm):   Diagnosis. From all other genera of Staphylininae the new genus can be recognized based on the following characters: antennomere 2 1.6× wider than antennomere 3; antennomere 11 3× longer than antennomere 10; penultimate segment of maxillary palpi large, covered in short setae, approximately 2× the length of apical segment; apical segment of maxillary and labial palpi aciculate. Head with 'infraorbital ridges' straight, extended to base of mandibles; postgenal ridge absent; frontoclypeal suture present; mesoventrite with transverse ridge present (incomplete medially); mesotrochanter and first mesotarsomere of males with black combs; tarsal formula 5-5-5; empodial setae long and parallel-sided; apical edge of sternites III to VI with randomly distributed acute projections; tergites VII and VIII with broader, foliose setae in addition to the usual acuminate, simple setae; apparent fusion of tergite X to lateral tergal sclerites in males.

Family
Differential diagnosis. The differential diagnosis is based on the recovered phylogenetic position of Amazonothops and its strong resemblance to the Amblyopinini genus Heterothops. Amazonothops differs from Atanygnathus Jacobson, 1909 (Tanygnathinini) in the number of tarsal segments (5-4-4 in Atanygnathus); short genae and normal shape of the apical labial and maxillary palpomere (extremely elongate and distinctly converging to apex in Atanygnathus); absence of dorsal setae on the apical tarsomere (present in Atanygnathus). It should be noted that some species of Atanygnathus have combs on the profemora (Adam Brunke, personal communication). Amazonothops differs from species of Holisus Erichson, 1839 (Hyptiomini) in the pronotal hypomeron strongly inflexed, not visible in lateral view and without longitudinal middle carina (visible in lateral view and with middle carina in Holisus), presence of empodial setae (absent in Holisus) and general appearance and habitus (Holisus is distinctly dorsoventrally flattened with coarse punctation). Amazonothops differs from the genus Natalignathus Solodovnikov, 2005, a hitherto unrecognized possible member of the same clade (see Discussion below) in the smaller body, short genae and much lesser elongate mouthparts, absence of dorsal setae on the apical tarsomere (present in Natalignathus) and presence of the combs. Amazonothops differs from Heterothops and other genera of Amblyopinini in presence of the frontoclypeal suture; antennomere 3 distinctly smaller than antennomeres 2 and 4; mesosternum with transverse ridge present (incomplete medially); apical edge of sternites III to VI with randomly distributed acute projections; tergites VII and VIII with broader, foliose setae in addition to the usual acuminate, simple setae; and apparent fusion of tergite X to lateral sclerites in males.
Abdomen. Protergal glands elongate, fringed by setae (Fig. 3F). Tergites with anterior transverse carina only. Tergite II as in Fig. 3G. Sternite III with evenly curved transverse carina, slightly projected medially. Tergite VII with white fringe along posterior edge. Apical edge of sternites III to VI with randomly distributed acute projections (Fig. 3H). Tergites VII and VIII with broader, foliose setae in addition to the usual acuminate, simple setae ( Fig. 4A-C).
Distribution. Based on the specimens studied here, the new genus is restricted to the lowland areas of the Amazonian basin of Peru.
Bionomics. Based on the available label data, the genus occurs in forested areas (100-420 m elevation) and has so far only been collected by flight intercept traps.
Etymology. The genus name is a combination of 'Amazon' and the genus name Heterothops, which the new genus strongly resembles superficially.
Remarks. The new genus is certainly morphologically distinct among other members of the subfamily Staphylininae and family Staphylinidae. Noteworthy is the secondary sexual dimorphism exhibited by Amazonothops. In males, the mesotrochanter and first mesotarsomere have distinct black combs which are completely lacking in females (Fig. 4F, G, H). The function, if any, of the combs remains unknown but very similar combs are commonly found within Amblyopinini, e.g., recently illustrated for Myotyphlus Fauvel, 1883 (Solodovnikov and Jenkins Shaw 2017).   Description. In addition to characters in the genus description, the species is characterized by the following primary and secondary male sexual characters. Sternite VIII without apical incision. Tergite X apparently fused to internal face of lateral sclerites (Fig.  5A, solid line), with two large setae situated at apical third of length ( Fig. 5A; LS). Sternite IX emarginate apically, with symmetrical basal stem (Fig. 5A, dashed line). Lateral tergal sclerites and tergite X of approximately equal length. Aedeagus (Fig. 5B, C); paramere longer than and closely attached to, median lobe (Fig. 5B); lateral apical area of paramere with setae of varying length ( Fig. 5C; ST); internal sac consisting of a pair of heavily sclerotized oblong-shaped sclerites ( Fig. 5C; OS) and pair of weakly sclerotised longer, more slender sclerites extruding from apical area of median lobe under pressure (Fig. 5C, SS). Distribution. Based on the specimens studied here, the new genus is restricted to the lowland areas of the Amazonian basin of Peru (Fig. 6). As a fully winged species known only from six specimens from two areas approximately 1000 kilometres apart from each other, it seems to be a widespread species, perhaps much more than it appears now.
Bionomics. Same as above.
Etymology. The species is named in honour of Aslak Kappel Hansen (NHMD) who was one of the collectors of this new genus and who brought our attention to its unusual nature compared to Heterothops.
Comments. It is notable that a species of Heterothops (Amblyopinini) was obtained during the same collecting event as one of the Amazonothops specimens. This shows that these two similar looking, yet phylogenetically distant (Fig. 1) taxa co-occur, probably in similar or the same microhabitats in the Amazon basin.

Discussion
The molecular phylogeny of Jenkins Shaw et al. (2019) placed Amazonothops sister to a peculiar clade formed by the tribes Tanygnathinini and Hyptiomini with maximal support (Fig. 1). As Jenkins Shaw et al. (2019) noted, the recovery of Amazonothops in a clade with Tanygnathinini and Hyptiomini also makes the somewhat similar South African endemic genus Natalignathus relevant when considering the sister relationships of Amazonothops. Natalignathus was originally placed in Tanygnathinini (Solodovnikov 2005) and later moved to Amblyopinini (then Amblyopinina) by Chatzimanolis et al. (2010). Although the phylogenetic study by Chatzimanolis et al. (2010) was molecular, Natalignathus was reclassified based on a morphological character assessment and not included in the analysis as DNA-grade material was not available. Besides, previous morphological studies considered it to be sister to Atanygnathus, itself considered a highly autapomorphic lineage nested within Amblyopinini, a pattern repeatedly revealed in morphology-based phylogenetic analyses since Solodovnikov (2006). Tanygnathinini were not sunk in synonymy to Amblyopinini by these authors because of their very clear morphological diagnosis and a lack of knowledge of the internal phylogeny of Amblyopinini. Chatzimanolis et al. (2010) were the first to link Holisus and Atanygnathus in an isolated clade within Staphylininae, though they are so different morphologically that this was suspected to be an artefact. However, this sister group relationship between Tanygnathinini and Hyptiomini, persisted through several later molecular (Brunke et al. 2016;Żyła and Solodovnikov 2019;Jenkins Shaw et al. 2019) and total evidence (Chani-Posse et al. 2018) phylogenetic studies with better and more diverse taxon and gene sampling. Unfortunately, Natalignathus remains unsampled for molecular phylogeny due to a lack of DNA-grade material. In view of the continued corroboration of the Tanygnathinini + Hyptiomini clade, and now with Amazonothops discovered as a sister group to that, it seems plausible that Natalignathus should belong to the Tanygnathinini + Hyptiomini clade as well, probably as a sister to Atanygnathus as was initially noted at the time of its description (Solodovnikov 2005). Even though peculiar, the morphology of Amazonothops seems less derived than either Holisus or Atanygnathus, showing some resemblance, and sharing some characters with, Natalignathus. Like Natalignathus, Amazonothops resembles and shares some characters with the early-diverging and plesiomorphy-rich 'Quediine-looking' lineages of Staphylininae, much more so than the derived Atanygnathus or Holisus. Amazonothops is clearly an important taxon for understanding of the origin the entire Tanygnathinini + Hyptiomini clade. Once the molecular data from Natalignathus is obtained, both it and Amazonothops should be included in a total evidence phylogenetic analysis to explore the early evolution of Staphylininae. Discovery of Amazonothops further highlights the rich and unknown biodiversity of the Peruvian Amazon and suggests a high probability that more species of this genus, or even new genera of this lineage maybe discovered there in the future.
With the recently updated classification of the subfamily Staphylininae  and the recovered phylogenetic position of Amazonothops (Jenkins Shaw et al. 2019), it is plausible that Amazonothops should be placed in its own tribe. Here we refrain from doing so pending further molecular and morphological exploration of the (Amazonothops (Atanygnathus + Holisus)) clade with broad outgroup sampling that would also include sampling many more ingroup species for the latter two sizeable genera, and revisiting Natalignathus.