Additions to the taxonomy of the Afrotropical Tetramorium weitzeckeri species complex (Hymenoptera, Formicidae, Myrmicinae), with the description of a new species from Kenya

This study presents a taxonomic update of the Tetramorium weitzeckeri species group. Tetramorium mpala sp. nov. is described from Laikipia, Kenya, and placed in the T. weitzeckeri species complex. In addition, we also provide an illustrated identification key to the three species complexes of the T. weitzeckeri species group, and an updated illustrated identification key to the species of the T. weitzeckeri species complex.


Introduction
The globally occurring myrmicine genus Tetramorium Mayr, 1855 is widespread throughout all zoogeographical regions and can be considered as hyper-diverse, with currently more than 545 valid species (Bolton 2013).It is a predominantly Old World genus with very few, mostly introduced, species found in the New World (Brown 1957;Bolton 1976Bolton , 1977Bolton , 1979Bolton , 1980;;Hita Garcia et al. 2010).Its main distribution, with ca.230 described species, lies in the Afrotropical region, where species of Tetramorium occupy a wide range of habitats, microhabitats and lifestyles not seen in any other region, which suggests a likely origin or diversifi cation centre within the Afrotropical region (Bolton 1976(Bolton , 1980;;Hita Garcia et al. 2010).The Malagasy Tetramorium fauna also shows a high degree of diversity, endemism, and often micro-endemism along its numerous isolated mountain ranges, but is less species-rich and holds much less morphological and ecological diversity than that of the Afrotropics.The combined and ongoing efforts of exhaustive inventories and large-scale revisions recently elevated the diversity in the Malagasy region from 39 species (Bolton 1979) to ca. 125 species (Hita Garcia & Fisher 2011, 2012a, 2012b;FHG unpublished data).Due to its global distribution and hyper-diversity, new species of Tetramorium are continuously being discovered and described on a global level (e.g., Europe: Czösz et al. 2007;Csösz & Schulz 2010;Central America: Vásquez-Bolaños 2007;Vásquez-Bolaños et al. 2011;Saudi Arabia: Sharaf et al. 2012;India: Bharti & Kumar 2012), but the bulk of the undescribed diversity is expected from the Afrotropical region.Even though Bolton (1980) revised the whole Afrotropical region and synonymized the former genus Triglyphothrix Forel, 1890 with Tetramorium (Bolton 1985), many undescribed species have been discovered in fi eld studies and in a score of museum collections by the authors (Hita Garcia et al. 2009Garcia et al. , 2010Garcia et al. , 2013, unpublished data), unpublished data).The taxonomy of two Afrotropical species groups was revised in recent years.In the fi rst study twelve out of 26 species of the T. weitzeckeri group were described as new species (Hita Garcia et al. 2010), while the second described one additional species of the T. tortuosum group, raising the African species count to three (Hita Garcia & Fisher 2013).With on-going taxonomic research and with additional material of undescribed species being generated by numerous fi eld studies, we expect that the diversity of Tetramorium in the Afrotropical region is likely to reach 350 to 400 species in the future.
In 2009 and 2010 during the revision of the T. weitzeckeri species group (Hita Garcia et al. 2010) we became aware of a potentially new species collected by the late Roy R. Snelling (Natural History Museum of Los Angeles County, Los Angeles, U.S.A.) in Laikipia, Kenya (R.R. Snelling unpublished notes).Snelling wrote in his notes about a new species commonly collected on the ground at Mpala Research Centre, which looked morphologically very close to T. weitzeckeri Emery, 1895 and T. guineense (Bernard, 1953) but differing from them in petiolar node shape and pilosity on the fi rst gastral tergite.During a research visit to the Snelling collection in 2009 we tried to fi nd this material, which supposedly consisted of a few collections from the ground at Mpala Research Centre.Unfortunately, even after a thorough search through the collection, there was no undescribed T. weitzeckeri group species from Laikipia to be found anywhere, and the revision of the species group was fi nished without including that mysterious species.Surprisingly, during a recent examination of unidentifi ed general Kenyan ant material collected by Snelling in 2001 at Mpala Research Centre, we encountered one specimen from an undescribed species belonging to the T. weitzeckeri species group.After a fi rst examination it became apparent that it was indeed the new species mentioned by Snelling in his unpublished notes.
In this study we describe that new species as Tetramorium mpala sp.nov.and integrate it into the existing taxonomic system of the T. weitzeckeri species complex/group.Accordingly, we provide an illustrated identifi cation key to the three species complexes of the T. weitzeckeri species group (T.edouardi complex, T. muralti complex, T. weitzeckeri complex) and an updated illustrated identifi cation key to the species of the T. weitzeckeri species complex.

Material and methods
The collection abbreviations follow Evenhuis (2013).The material upon which this study is based is located and/or was examined at the following institutions: The only available specimen of T. mpala sp.nov.was deposited in the collection of LACM.Most of the material used for the recent revision of the whole T. weitzeckeri species group (Hita Garcia et al. 2010), especially the most recent collections, can be found in the collections of BMNH, CASC, LACM and ZFMK, while older type material is mostly located at BMNH, MCZ, MHNG and NHMB.The new type and all imaged specimens can be uniquely identifi ed with specimen-level codes affi xed to each pin (e.g., CASENT0247445).
Digital colour images of the new species were created using a Leica DFC 425 camera in combination with the Leica Application Suite software (version 3.8).All images presented are available online and can be consulted on AntWeb (http://www.antweb.org).The measurements were taken with a Leica MZ 12.5 equipped with an orthogonal pair of micrometers at a magnifi cation of 100×.Measurements are expressed in mm to two decimal places.The measurements and indices used in this study follow Hita Garcia & Fisher (2011, 2012a, 2012b, 2013) Note that the petiole and postpetiole were measured differently.For the petiole, only the petiolar node was measured, excluding the peduncle, as the node has proved to be of high diagnostic value (Hita Garcia et al. 2010).Measurements of the whole petiole, peduncle plus node, would mask these important differences between species.In contrast, we measured the whole postpetiole because it was rounded in most species and without a distinct peduncle-like structure.As a consequence, some information can be lost in the few species with a moderately or strongly anteroposteriorly compressed postpetiole.Even so, the postpetiole measurements as defi ned still permit better comparisons for most species.

Identifi cation key to Afrotropical species complexes of the T. weitzeckeri species group (workers)
In Hita Garcia et al. (2010) we provided a key to all species from all three species complexes without a special key to these complexes.In order to facilitate species identifi cations and species group placements in the future, we provide a simple key to the complexes here: 1. Antennal scrobe well developed and usually deep, with a distinct and often sharp margin all around, frontal carinae curve down ventrally between posterior eye level and occipital margin to form the posterior and ventral margins of the antennal scrobe, in a few species posterior margin weak but still visible; sculpture on cephalic dorsum often reduced, generally 3 or fewer rugae present between frontal carinae, in a few species up to 5 or 6, never more (Fig. 1A-B, E-F) ......T. muralti complex -Antennal scrobe developed, but shallow, never with a sharp margin all around, frontal carinae almost reaching occipital margin and functioning as dorsal margin of antennal scrobe, ventral margin of antennal scrobe never differentiated; sculpture on cephalic dorsum never reduced, always at least 7 (generally distinctly more) longitudinal rugae present between frontal carinae (Fig. 1D, G-H) .........2 2. Petiolar node distinctly squamiform, in profi le between 2.3 and 4.0 times higher than long (LPeI 25-43), shape in dorsal view always strongly transverse and elliptical, and between 2.2 and 3.7 times wider than long (DPeI 219-367) (Fig. 2A-B, E-F) .........T. weitzeckeri complex -Petiolar node high nodiform, in profi le around 1.3 to 2.0 times higher than long (LPeI 50-80), shape in dorsal view never elliptical or transverse, more an irregular polygon with rounded corners, and between 1.   (Weber, 1943) = Tetramorium weitzeckeri nigellus (Santschi, 1932)

Notes on biogeography and identifi cation
New material has become available since the last revision of the T. weitzeckeri species group (Hita Garcia et al. 2010); subsequently, the distribution ranges of a few species need to be adjusted.Fresh material from an ongoing inventory of the ant fauna of Gorongosa National Park in Mozambique revealed the presence of T. humbloti, T. sepultum and T. weitzeckeri.Even though their presence in Mozambique is not surprising, all three were previously unknown from that country.Hita Garcia et al. (2010) reported the absence of T. humbloti from Kenya, but some freshly identifi ed material from the area around Nairobi clearly belongs to this species.The distribution range of T. tanaense is also larger than previously understood.It is now known from the forest of Arabuko Sokoke on the Kenyan coast, which is close to the type locality, and from Ndimba Forest Reserve located in south-eastern Tanzania close to the Indian Ocean.
Despite these new fi ndings, the biogeographic composition of the complex has not changed signifi cantly.
Tetramorium boltoni, T. guineense, T. renae and T. snellingi are species found predominantly in the equatorial rainforest belt, whereas the species T. humbloti, T. sepultum and T. weitzeckeri are distributed in the drier eastern and southern parts of sub-Saharan Africa.Tetramorium tanaense seems to be endemic to the coastal forests of Eastern Africa in Kenya and Tanzania, and T. bendai is only known from one collection in Burundi (without any ecological information at all).Tetramorium mpala sp.nov.also seems to have a very restricted distribution because it is only known from its type locality in Central Kenya.
In addition, several non-taxonomists have used the identifi cation key published in Hita Garcia et al.
(2010) and, fortunately, provided feedback to us.The key seemed to have worked mostly well, but users drew attention to some problems in the key not anticipated back in 2010.These problems were mainly located in the part of the key dealing with the T. weitzeckeri species complex, especially the separation of T. guineense from T. weitzeckeri.Some series of the latter species from Tanzania and South Africa possess strongly developed cephalic ground sculpture almost as distinct as seen in T. guineense, which causes diffi culties with the key, even though both species are certainly not conspecifi c and differ in various aspects.Consequently, we have modifi ed the identifi cation key to include these users' fi rst-hand experience in order to make the discrimination of T. guineense from T. weitzeckeri easier, as well as several other minor changes throughout the key.

Identifi cation key to species of the T. weitzeckeri species complex (workers)
1. First gastral tergite without any form of standing pilosity (Fig. 3A

Diagnosis
The character combination of very large eyes (OI 31) and fi rst gastral tergite with long, fi ne decumbent to subdecumbent (rarely appressed) pilosity distinguishes T. mpala from the remainder of the T. weitzeckeri species complex.Head longer than wide (CI 94); posterior head margin in full-face view fl at to weakly concave; anterior clypeal margin with distinct median impression; frontal carinae strongly developed, distinctly raised, and very long, approaching or ending at posterior head margin; antennal scrobes present, but shallow and without clearly defi ned posterior and ventral margins.Antennal scapes of moderate length, not reaching posterior head margin (SI 81).Eyes very large (OI 31).
Mesosomal outline in profi le weakly to moderately convex, moderately marginate from lateral to dorsal mesosoma, comparatively high and stout (LMI 42); promesonotal suture present, weak but clearly visible; metanotal groove well developed and in profi le moderately deep.Propodeal spines long, spinose and acute (PSLI 35); propodeal lobes short, triangular and blunt.Petiolar node squamiform to thinly high cuneiform and slightly triangular, in profi le three times higher than long (LPeI 33), anterodorsal and posterodorsal margins relatively rounded and posterodorsal margin less well developed than anterodorsal, petiolar dorsum tapering backwards; node in dorsal view of strongly transverse elliptical shape, around 2.9 times as wide as long (DPeI 292).Postpetiole in profi le subglobular to weakly anteroposteriorly compressed, approximately 1.5 times as high as long (LPpI 68); in dorsal view around 1.6 times as wide as long (DPpI 162).Postpetiole in profi le appearing higher and more voluminous than petiolar node, in dorsal view 1.2 times as wide as petiolar node (PPI 120).
Mandibles striate; clypeus longitudinally rugulose with six more or less irregular rugulae, median rugula not well developed; cephalic dorsum between frontal carinae irregularly longitudinally rugose with around eight rugae, rugae running from posterior clypeal margin to posterior head margin, but some broken, meandering or with cross-meshes; scrobal area partly unsculptured, but mostly merging with surrounding reticulate-rugose to longitudinally rugose sculpture present on lateral and ventral.Mesosoma laterally and dorsally longitudinally rugose, laterally slightly more irregularly so.Forecoxae unsculptured, smooth and shining.Both waist segments and gaster completely unsculptured, smooth and shining.Ground sculpture generally faint to absent everywhere on body.Head with moderately abundant standing pilosity; mesosoma with six pairs of long, fi ne, standing hairs; petiole with three pairs of long, fi ne, standing hairs and postpetiole with four pairs of subdecumbent to decumbent, long, fi ne hairs; fi rst gastral tergite with fairly long, fi ne and subdecumbent to decumbent pilosity.Anterior edges of antennal scapes and metatibiae with appressed hairs.Body colouration chestnut brown to dark brown, appendages lighter in colour and gaster much darker than remainder of body.

Etymology
The name of the new species is inspired by the type locality, the Mpala Research Centre, which is an important research facility in Kenya.The species epithet is a nominative noun in apposition and thus invariant.

Distribution and ecology
Tetramorium mpala sp.nov. is currently only known from the type locality (Fig. 12) where it was collected in acacia woodland savannah at an elevation of 1650 m.The holotype was sampled on the ground, but until more material becomes available it remains unclear whether that is the primary stratum of T. mpala.

Discussion
The new species is readily distinguishable within the T. weitzeckeri species complex.The most obvious character is certainly the pilosity on the fi rst gastral tergite, which is long, fi ne and subdecumbent to decumbent in T. mpala sp.nov., whereas the remainder of the complex either lacks any long pilosity at all (T.bendai, T. humbloti, T. sepultum and T. tanaense) or possesses long, suberect to erect pilosity (T.boltoni, T. guineense, T. renae, T. snellingi and T. weitzeckeri).The second-best character is eye size, European Journal of Taxonomy 90: 1-16 (2014) since T. mpala sp.nov.has the largest eyes (OI 31) encountered in the species complex, which contrast with the generally much smaller eyes of the other species (usually OI 16-26, only a few specimens of T. humbloti and all of T. tanaense have OI 27-29).
Another aspect that deserves attention here is the shape of the petiolar node in T. mpala.It is clearly squamiform like in all species of the T. weitzeckeri complex, but also similar to the high cuneiform and slightly triangular form found in some species of the Afrotropical T. squaminode species group (Bolton 1980) or the Malagasy T. marginatum and T. bonibony species groups (Hita Garcia & Fisher 2012a).As already noted by Bolton (1980) and later by Hita Garcia et al. (2010), there seems to be a close relationship between the 11-segmented T. weitzeckeri group (especially the T. weitzeckeri complex) and the 12-segmented T. squaminode group, mainly on the basis of the spatulate sting appendage and the squamiform petiolar node.T. mpala sp.nov.appears to be an additional argument for a close relationship between these groups since its petiolar node shape is intermediate.However, at present, without a taxonomic revision of the T. squaminode group and a broader phylogenetic analysis of the genus Tetramorium as a whole, we prefer to keep these groups separate.
Unfortunately, the new species is at present known only from the holotype.In general, it is not recommendable to describe new species on the basis of just one specimen, since it is not unlikely that species based on singletons could just be variant forms of already known and valid species.Nevertheless, in the case of T. mpala sp.nov.we are very confi dent that this is not the case.The character combination of T. mpala sp.nov.outlined above is very unique, and there is no obvious morphological connection to another species of the T. weitzeckeri species complex or the entire T. weitzeckeri species group.In fact, there is no evidence at all that T. mpala sp.nov.could be a variation of another species from the T. weitzeckeri complex.Furthermore, T. mpala sp.nov.co-occurs at Mpala with other members of the T. weitzeckeri species group (T.edouardi Forel, 1894, T. zonacaciae (Weber, 1943) and T. weitzeckeri), but is easily separable from these.Consequently, we prefer to describe the new species and make it available for ant research.Hopefully, further ant sampling at Mpala Research Centre will provide more material of this interesting species.
BMNH = The Natural History Museum (British Museum, Natural History), London, U.K. CASC = California Academy of Sciences, San Francisco, California, U.S.A. LACM = Natural History Museum of Los Angeles County, Los Angeles, California, U.S.A. MCZ = Museum of Comparative Zoology, Cambridge, Massachusetts, U.S.A. MHNG = Muséum d'Histoire Naturelle de la Ville de Genève, Geneva, Switzerland NHMB = Naturhistorisches Museum, Basel, Switzerland ZFMK = Zoological Research Museum Alexander Koenig, Bonn, Germany : HL = Head length: maximum distance from the mid-point of the anterior clypeal margin to the mid-point of the posterior margin of the head, measured in full-face view.Impressions on anterior clypeal margin and posterior head margin reduce head length HW = Head width: width of head directly behind the eyes measured in full-face view SL = Scape length: maximum scape length excluding basal condyle and neck EL = Eye length: maximum diameter of compound eye measured in oblique lateral view PH = Pronotal height: maximum height of pronotum measured in lateral view PW = Pronotal width: maximum width of pronotum measured in dorsal view WL = Weber's length: diagonal length of mesosoma in lateral view from the postero-ventral margin of the propodeal lobe to the anterior-most point of the pronotal slope, excluding the neck PSL = Propodeal spine length: the tip of the measured spine, its base, and the centre of the propodeal concavity between the spines must all be in focus.Using a dual-axis micrometer the spine length is measured from the tip of the spine to a virtual point at its base where the spine axis meets orthogonally with a line leading to the median point of the concavity PTH = Petiolar node height: maximum height of petiolar node measured in lateral view from the highest (median) point of the node to the ventral outline.The measuring line is placed at an orthogonal angle to the ventral outline of the node PTL = Petiolar node length: maximum length of the dorsal face of the petiolar node from the anterodorsal to the posterodorsal angle measured in dorsal view PTW = Petiolar node width: maximum width of dorsal face of petiolar node measured in dorsal view PPH = Postpetiole height: maximum height of the postpetiole measured in lateral view from the highest (median) point of the node to the ventral outline.The measuring line is placed at an orthogonal angle to the ventral outline of the node PPL = Postpetiole length: maximum length of postpetiole measured in dorsal view PPW = Postpetiole width: maximum width of postpetiole measured in dorsal view OI = Ocular index (EL / HW × 100) CI = Cephalic index (HW / HL × 100) SI = Scape index (SL / HW × 100) DMI = Dorsal mesosoma index (PW / WL × 100) LMI = Lateral mesosoma index (PH / WL × 100) PSLI = Propodeal spine index (PSL / HL × 100) PeNI = Petiolar node index (PTW / PW × 100) LPeI = Lateral petiole index (PTL / PTH × 100) DPeI = Dorsal petiole index (PTW / PTL × 100) PpNI = Postpetiolar node index (PPW / PW × 100) LPpI = Lateral postpetiole index (PPL / PPH × 100) DPpI = Dorsal postpetiole index (PPW / PPL × 100) PPI = Postpetiole index (PPW / PTW × 100)

Fig. 12 .
Fig. 12. Map of sub-Saharan Africa showing the type locality of Tetramorium mpala sp.nov.