Pheidole Afrotropical species groups

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Morphological species groups for the Pheidole of the Afrotropical region have been defined by Fischer, G., Hita Garcia, F., & Peters, M.K. 2012. Taxonomy of the ant genus Pheidole Westwood (Hymenoptera: Formicidae) in the Afrotropical zoogeographic region: definition of species groups and systematic revision of the Pheidole pulchella group. Zootaxa, 3232, 1-43.

They preface details about the species groups with the following:

We provide diagnostic definitions for six species groups based on morphology. Species within these groups share important characteristics in shape and proportions of head and mesosoma, relative length of appendages in general, and scape and metafemur length in particular. These are related to life history traits and ecology of the species (Weiser & Kaspari, 2006). Furthermore, important diagnostic characters include postpetiole proportions and modifications (i.e. ventral and lateral processes), and the overall pattern of body sculpture. The latter is generally variable within species groups and between species, ranging from densely punctate to almost completely smooth and shiny. Nevertheless, intraspecifically the sculpture-patterns are consistent, except for some minor and sporadic differences in the expression among different populations. Pilosity is another good diagnostic character, and is suitable for the division of species into groups with major differences in length, thickness, and overall abundance of hairs. Our species group definitions are provisional and are likely to change when more material is available. Phylogenetic analysis will be necessary to test the monophyly of our groups, but in the mean time they serve a useful function to aid identification and to break the species into clusters for revision.

Currently, 136 valid taxa are listed for the Afrotropical region (Bolton & Alpert, 2009), with the actual number of species being undoubtedly higher. Most of the tropical forests and other species rich habitats remain unsampled, and museum collections already store many undescribed species.

aurivillii group

Larger species (minor worker HW: 0.52–0.79 mm, n=52) with relatively long appendages (SI: 107–145, FI: 142–247). Minor workers: characterized by oval head that is longer than wide, long promesonotum, declining slowly to metanotal groove, absent or inconspicuous mesonotal process. Sculpture on mesonotum, mesopleuron and propodeum uniform, pilosity relatively long, erect and flexous. Postpetiole with shallow ventral process. Major workers: head with mostly irregular rugose-punctate sculpture. Frontal carinae and antennal scrobe absent or inconspicuous, inner hypostomal teeth developed to large, mesonotal process and postpetiole ventral process present. Pilosity as in minor and very abundant. Four described subspecies (Pheidole aurivillii, Pheidole aurivillii attenuata, Pheidole aurivillii kasaiensis and Pheidole aurivillii rubricalva), plus other potentially related species and several undescribed morphospecies probably belong to this group.

excellens group

Species with square-like heads in both, minor and major workers, shorter appendages (minor worker SI: 86–115, n=32), often extensive and coarse body sculpture (sometimes only on pronotum), abundant and fine pilosity and small postpetioles, in major workers with a lateral process.

Minor workers: characterized by wide, square head with straight posterior margin and subangulate to angulate corners, relatively short scape, barely to moderately exceeding occipital margin. Postpetiole very short, lower than petiole, about as wide as long. Body often deeply punctate-rugulose/rugose [e.g. excellens Mayr, liengmei Forel], with coarse ridges along dorsopropodeum, but some species mostly smooth [sculpturata rhodesiana Forel], to superficially sculptured [sculpturata]. Usually with high amount of very thin and moderately short body pilosity, often pelt-like, at least on the head. Spines short to long, linearly spinose. Major workers: head usually elongate, much longer than wide, or at least square-like with parallel to subparallel sides, sometimes wider anteriorly than posteriorly. Submedian and outer hypostomal teeth well-developed to large, median tooth absent. Promesonotal dome high, spines quasi-vertical, often thick, blunt or truncated. Postpetiole laterally with an (often strongly) extended, wing-like, posteriorly curved process. Pilosity and sculpture similar to minor workers. The group can be subdivided into two different complexes, one with small species (katonae complex; minor worker HW: 0.57–0.63, n=8), possessing short legs and spines, and relatively larger eyes:Pheidole katonae, Pheidole sculpturata zambesiana. The other complex consists of larger species (excellens complex; minor worker HW: 0.69–0.93, n=24), which possess longer legs and spines, and relatively smaller eyes: Pheidole excellens, Pheidole liengmei, Pheidole njassae, Pheidole sculpturata, Pheidole sculpturata welgelegenensis. The described species belonging to this group are: Pheidole arnoldi, Pheidole excellens, Pheidole excellens weissi, Pheidole katonae, Pheidole liengmei, Pheidole liengmei micrartifex, Pheidole liengmei shinsendensis, Pheidole njassae, Pheidole sculpturata, Pheidole sculpturata areolata, Pheidole sculpturata berthoudi, Pheidole sculpturata dignata, Pheidole sculpturata rhodesiana, Pheidole sculpturata welgelegenensis, Pheidole sculpturata zambesiana. Several probably undescribed morphospecies are located in the collections of The Natural History Museum, California Academy of Sciences and Zoologisches Forschungsinstitut und Museum Alexander König.

megacephala group

Relatively small species (minor worker HW: 0.51–0.66 mm, n=18), with relatively short appendages (SI: 117–122, FI: 106–129) and spines. Minor workers: posterior head margin weakly rounded and eyes with eight or more ommatidia in the longest row. Promesonotum without mesonotal process and often smoothly declining towards metanotal groove, spines very short or minute. Petiole relatively short, postpetiole comparatively large with ventral process. Major workers: head in full-face view often broadest at mid-point or posterior, anteriorly often narrower, head sometimes slightly heart shaped. Longitudinal rugulae mostly ending on frons, upper half of head usually smooth and shiny, antennal scrobe weak to inconspicuous, inner hypostomal teeth mostly very small or inconspicuous and medium tooth absent. Mesosoma, petiole and postpetiole similar to minor workers. A number of described species and infraspecific taxa exist for this group (Pheidole megacephala costauriensis, Pheidole megacephala duplex, Pheidole megacephala ilgii, Pheidole megacephala impressifrons, Pheidole megacephala melancholica, Pheidole megacephala nkomoana, Pheidole megacephala rotundata, Pheidole megacephala scabrior, Pheidole megacephala speculifrons, Pheidole megacephala talpa, Pheidole picata, Pheidole picata bernhardae, Pheidole picata gietleni, Pheidole punctulata, Pheidole punctulata atrox, Pheidole punctulata spinosa), which is in high need of revision.

nigeriensis group

Very small species (minor worker HW: 0.41–0.56 mm, n=60), with short scapes and legs (SI: 90–114, FI: 95–122). Minor workers: posterior head margin straight to weakly concave and eyes small with a maximum of six ommatidia in the longest row. Promesonotal dome well-rounded to slightly angulate in profile view, propodeum, spines and postpetiole relatively short. Postpetiole not higher than petiolar node and without ventral process. Major worker: head longer than wide, very large compared to the rest of the body, anteriorly weakly longitudinally rugulose. Upper half of head mostly smooth (similar to megacephala group), inner hypstomal teeth well-developed to relatively large. Mesosoma, petiole and postpetiole similar to minor workers. The group contains Pheidole nigeriensis and several morphospecies collected from different localities.

pulchella group

A key to the pulchella group species

FIGURE 1 A) Pheidole pulchella, full-face view of minor worker: the two lines show the lateral clypeal carinae on the sides of the clypeus (1). B) P. pulchella, lateral view of minor worker: illustrating posterior head margin with a weakly developed occipital carina (2), promesonotum with inconspicuous humeri (3), and second mesonotal process not reduced (4). C) P. pulchella, lateral view of major worker: illustrating second mesonotal process reduced to a small ridge anterior of the metanotal groove (5) and well-developed metapleural carina (6) situated above the metapleural gland scrobe (7). D) P. pulchella, in oblique fronto-dorsal (dorsocaudad) view (Will Ericson 2011): measurement of propodeal spine length (PSL), the bold line representing the measurement, bordered by the perpendicular line across the base of the spine.

Relatively large species (minor worker HW: 0.66–0.97 mm (n=154), major worker HW: 1.63–2.35 (n=53)), with relatively long spines in both, minor (PSLI: 21–40) and major workers (PSLI: 11–19), which are usually curved backwards, except in P. diomandei. Minors always with a distinct promesonotal process, followed by a well-developed or conspicuous smaller process (Fig. 1B–4) and a distinctly impressed metanotal groove. Majors always with a distinct promesonotal process and hypostomal margin of the head always with two conspicuous inner and two outer submedian teeth, but lacking the median process.

Both worker subcastes with a well-developed postpetiolar ventral process, similar to the species of the megacephala complex, but distinctly separated from them by the previous character combination.

Minor workers: head shape in full-face view variable among species, but never square with angulate posterolateral corners, from short and rounded (CI: 85–98) with sides of head strongly convex, posterior margin convex (Pheidole dea), or almost straight (Pheidole rebeccae), to long-elliptical (CI: 73–84), sub-angular at eye-level and posteriorly elongate towards occipital carina (Pheidole christinae, Pheidole heliosa). Mandibles smooth and shiny, sometimes with very superficial rugulae, laterally with weak longitudinal rugulae. Eyes situated near midlength of the head, of medium size (EI: 19–29). Scapes moderately to very long (SI: 102–174) and surpassing posterior head margin by one quarter to approximately one third of their length. Occipital carina always conspicuous in full-face view. Mesonotal declivity interrupted by promesonotal process, followed by a smaller process between promesonotal process and metanotal groove. The second, smaller, process is reduced and less conspicuous in some species. Propodeal spines long and spinose, much longer than distance between their bases (PSLI: 21–40), curved posteriorly towards petiole, rarely straight. Promesonotum, in lateral view, with angulate to subangulate edges, pronotal dorsum flat to weakly rounded, never strongly convex. Petiole longer than postpetiole (PpLI: 117–223), and in dorsal view usually about half as wide (PpWI: 152–232). Postpetiole also with well-developed convex ventral process and about as high as long, with subglobular to globular shape in profile. In dorsal view postpetiole about as long as wide, with a roughly trapezoidal shape. Pilosity with few to many long acute standing hairs, some species with hair apices truncate (or bifurcate), but in some species almost completely absent from dorsum of head, meso- and metasoma. Mesonotum and propodeum often with shorter, suberect to subdecumbent hairs. Standing hairs never very short and stiff. Between long erect hairs on head often shorter suberect to subdecumbent hairs present. Sculpture variable between species, with relatively little intraspecific variation, from completely and strongly punctate (Pheidole nimba) to mostly smooth and shiny (Pheidole rebeccae), but mesonotum and propodeum never completely smooth and shiny, at least partly punctate.

Major workers: head about as wide as long (CI: 96–105), broadest always between eye level and occipital margin, frons and sides of head rugose-punctate to varying degrees. Posterolateral lobes often differently sculptured. Dorsal surface of mandible smooth, laterally longitudinally rugulose. Clypeus with median longitudinal carina present. Scapes moderately long (SI: 49–58). Hypostomal margin always with two inner and two outer submedian teeth present, median process absent to inconspicuous. In full-face view, and for all species but P. heliosa, head margin without projecting hairs of any kind, only with relatively short appressed pilosity and long erect hairs, that are visible in lateral view. Pilosity on scape appressed to subdecumbent. Humeral area laterally not or weakly produced, mesonotal process always developed and with posterior steep declivity towards metanotal groove, which, in lateral view, is barely to broadly impressed. Propodeal spines relatively long and spinose, longer than distance between their bases. Petiole longer than postpetiole (PpLI: 131–176). Postpetiole considerably wider than petiole (PpWI: 177–252), wider and higher than long, in lateral view with anteriorly produced ventral process. Pilosity and sculpture similar to minor workers.

Pheidole batrachorum, Pheidole christinae, Pheidole darwini, Pheidole dea, Pheidole glabrella, Pheidole heliosa, Pheidole nimba, Pheidole pulchella, Pheidole rebeccae, Pheidole semidea, Pheidole setosa

The Pheidole pulchella species group was defined in the process of our identification efforts of two very distinct groups of specimens from the Kakamega Forest in Western Kenya and from the Budongo and Rabongo Forests in Uganda. Both were at first identified as P. pulchella. Comparison with type material later revealed the dark colored morphospecies to be conspecific with P. dea Santschi from the Democratic Republic of Congo. We are now able to describe the previously unknown major workers. The orange colored specimens from Budongo Forest belong to a previously undescribed species and are likely to be closely related to P. pulchella. In subsequent type material examinations and museum visits, additional undescribed material was found from the Ivory Coast in the West, along the equatorial rainforest belt to Gabon, Central African Republic, towards Kenya and Tanzania in the East. In their general morphology the species in this group are well separated from those of other groups.

Most of the collection localities for species of the P. pulchella group are in rainforests; habitats of a few are not indicated on the labels. Specimens were caught in pitfall-traps, leaf-litter extractions, by beating of the lower vegetation, or by hand-collection. Thus, the species in this group are most likely forest specialists living and/or foraging on the ground and in the lower vegetation. Their conspicuous morphology with the relatively large size, long spines and appendages, and well-developed eyes indicates that these species are not living within, but rather upon or above the leaf-litter layer. They possibly nest in dead wood, because several of the specimens, especially the more rarely observed majors, were collected from rotten logs. Still, the biology of this species group is largely unknown and there are no records or observations available, other than the collection data mentioned on the labels.

speculifera group

Medium to large species (minor worker HW: 0.52–0.81 mm, n=26), the minor workers characterized by large relatively long appendages (SI: 111–123), and both worker subcastes with large postpetiole that is 2–3 times wider than long. Minor workers: long antennal scapes, surpassing the posterior head margin by about 1/4 of their length. Posterior head margin compressed, weakly rounded (prelli complex) to evenly rounded (crassinoda, speculifera). Postpetiole large and voluminous, as long as [prelli complex] or longer (crassinoda, speculifera) than petiole and more than twice as wide. Pilosity moderately abundant, either short and stout, with blunt or split apices [crassinoda, prelli] or longer and flexous [speculifera].

Major workers: head either massive and thick, with sculpture variable, frontal carinae & antennal scrobes absent, inner hypostomal teeth strongly reduced and median tooth absent [speculifera complex] or head less massive, with strong longitudinal and transverse rugose-punctate sculpture, long, curved and broadly extended frontal carinae, inner hypostomal teeth and median tooth present and conspicuous [prelli complex]. Spines thick and short, almost lobate. Postpetiole very massive, in dorsal view about 2–3 times wider than petiole, with a conspicuously spiked lateral process. The group can be subdivided into prelli complex and speculifera complex, the former with slightly smaller species (minor worker HW: 0.52–0.56 mm, n=5), which possess relatively large eyes (EI: 31–33) (Pheidole caffra, Pheidole caffra abyssinica, Pheidole caffra amoena, Pheidole caffra bayeri, Pheidole caffra montivaga, Pheidole caffra senilifrons, Pheidole prelli, Pheidole prelli ingenita, Pheidole prelli redbankensis). The speculifera complex includes slightly to considerably larger species (minor worker HW: 0.60–0.81 mm, n=21) with smaller eyes (EI: 22–28) (Pheidole crassinoda, Pheidole crassinoda pluto, Pheidole crassinoda ruspolii, Pheidole crassinoda sordidula, Pheidole occipitalis, Pheidole occipitalis adami, Pheidole occipitalis neutralis, Pheidole speculifera, Pheidole speculifera ascara, Pheidole speculifera bispecula, Pheidole speculifera cubangensis). New material and undescribed species from different localities can be found in the collections of The Natural History Museum, California Academy of Sciences and Zoologisches Forschungsinstitut und Museum Alexander König.