Cephalotes Species Groups

The following is based on de Andrade, M. L.; Baroni Urbani, C. 1999. Diversity and adaptation in the ant genus Cephalotes, past and present. Stuttgarter Beitrage zur Naturkunde Series B (Geolgie and Palaontologie). 271:1-889.

atratus clade

 * Cephalotes alfaroi
 * Cephalotes atratus
 * Cephalotes marginatus
 * Cephalotes oculatus
 * Cephalotes opacus
 * Cephalotes placidus
 * Cephalotes serraticeps

This clade corresponds to the former genera Cephalotes and Eucryptocerus. It is characterised by two synapomorphies among the characters we tentatively retained for our data matrix: (1) the bispinose vertexal border, a character which, in this order of magnitude, is uniquely derived among the members of this group but appears to be paralleled by some (certainly homoplastic) denticles to be found among other species like Cephalotes borgmeieri, Cephalotes betoi, etc.; (2) the presence of a pair of dorsal pronotal spines, another character derived uniquely for the members of this clade but which appears to have been ( ?secondarily) lost among very small atratus and opacus workers. The absence of a soldier caste, which we stressed as a significant plesiomorphic trait of the hamulus clade, is still recognisable among some members of the atratus clade: there is at least one species certainly without morphologically differentiated soldiers (atratus) but the worker caste, in this case, is slightly polymorphic in size. Other species, like oculatus and placidus, are still known from too few specimens as to permit definitive conclusions about their polymorphism. The members of this clade are among the largest Cephalotes. Only some species of the clypeatus clade approach their size.

basalis clade

 * Cephalotes basalis
 * Cephalotes brevispineus
 * Cephalotes complanatus
 * Cephalotes cordiae
 * Cephalotes cordiventris
 * Cephalotes femoralis
 * Cephalotes inca
 * Cephalotes manni
 * Cephalotes mompox
 * Cephalotes ramiphilus

A relatively large clade containing nine Recent and one fossil species. It is characterized by the following synapomorphies: (1) worker propodeum with a pair of spines shorter than the basal face, a trait secondarily lost among the more specialized species inca and basalis; (2) worker with incrassate fore femora, a character invariant within the clade and similar but probably not homologous to the condition characteristic of Procryptocerus, and, (3) soldier without vertexal denticles. In our reconstruction this character state results as a secondary loss of the clade which should have been re-gained among the most specialised species basalis and cordiventris.

clypeatus clade

 * Cephalotes clypeatus
 * Cephalotes membranaceus
 * Cephalotes ustus

A small (three species), very distinctive clade characterised by the following four synapomorphies: (1) vertexal angles of the worker triangular, (2) worker CI > 155, (3) worker pronotal spines fused with a lamella, (4) propodeal spines fused with a lamella. The triangular vertexal angles appear, homoplastically, also among workers of some of the species of the basalis clade. The high CI value, outside this clade, appears only in the basalmost species of the next closely related clade (the multispinosus clade): the Mexican fossil Cephalotes poinari. The three representatives of this clade had been formerly considered as a separate genus: Zacryptocerus s. str. If, on one hand, the synapomorphies listed above would be sufficient for the characterization at generic level of these three species, such a decision is rendered impossible by the examination of our cladogram since it would render paraphyletic any other generic distinction of its most related species.

depressus clade

 * Cephalotes betoi
 * Cephalotes borgmeieri
 * Cephalotes cordatus
 * Cephalotes cristatus
 * Cephalotes depressus
 * Cephalotes eduarduli
 * Cephalotes palustris
 * Cephalotes pavonii

A medium-sized clade containing eight Recent species with a broad tropical distribution. It is characterised by the following three synapomorphies: (1) worker propodeum with a pair of spines followed by a tooth (char. 43, state 1), (2) worker petiole with indistinct anterior and posterior faces (char. 50, state 2), and, (3) aedeagus internally concave (char. 126, state 2). Synapomorphies (1) and (3) appear very robust and support entirely the separation of this clade. The shape of the worker petiole appears less convincing, and we suppose that its resulting synapomorphic value may be attributed either to our imprecise coding of it or to an artifact of character optimisation. Members of this clade are the first compact group of species the soldiers of which show either an in incipient or a complete cephalic disc. All remaining 79 more terminal species of the genus, except the problematic Cephalotes bruchi the soldier of which has an incipient disc only, have completely developed cephalic discs. Kempf (1951) intuitively recognised a "pavonii group" roughly similar to our depressus clade. The main difference between our and Kempf’s groupings of species (besides the trivial addition of new species in this paper) is our exclusion from the depressus clade of Cephalotes multispinosus and Cephalotes biguttatus, two species that we rank within our multispinosus clade, a clade very close but paraphyletic to the depressus clade.

hamulus clade

 * Cephalotes argentiventris
 * Cephalotes auricomus
 * Cephalotes flavigaster
 * Cephalotes hamulus
 * Cephalotes resinae
 * Cephalotes taino
 * Cephalotes unimaculatus
 * Cephalotes vinosus

This clade corresponds to the former genus or subgenus Hypocryptocerus and contains all the less specialised species of the genus Cephalotes. It is characterised by only three synapomorphies: (1) the vertexal angles broad, round and with crenulate margin, (2) the outer face of tibiae with longitudinal, irregular rugae, a character shared homoplastically also with the far relative rohweri (a member of the phylogenetically distant wheeleri clade) and with some species of the sister genus Procryptocerus, and, (3) petiolar spines present but shorter than 1/3 of the petiolar length, a character re-appearing in a number of distantly related, more specialised Cephalotes species. We regard this as an additional demonstration of the inappropriateness of considering Hypocryptocerus as a valid genus. We shall name the species of this group as hamulus clade for uniformity with other, comparable, phyletic lines we recognize within Cephalotes. Since the name Hypocryptocerus already exists in the literature, there are, however, no serious reasons against the use of this name as a subgeneric name for those preferring this formal solution.

Practically, if one disposes of abundant Cephalotes nest series, he should be able to recognise the members of the hamulus clade at glance by their possibly unique possession of one very important plesiomorphy: the absence of soldiers and the monomorphism of the worker caste, a character state unknown in other Cephalotes (though it may be present in the poorly known species Cephalotes placidus and Cephalotes oculatus in the atratus clade), but which is the rule among the species of the sister genus Procryptocerus.

Within the hamulus clade we recognise eight valid species and there is a possible, insufficiently known, ninth species. All these species are presumably endemic on the Island of Hispaniola and two of them are known only from copal samples of probable historical age. One could expect to encounter them again in the Recent fauna of the island.

A circumstance apparently contrasting with the antiquity of the clade is that its members are very similar each other and are likely to be the product of relatively young speciation events, a hypothesis supported also by palaeogeographic evidence. The main diagnostic characters among them appear to be confined to integumental sculpture, pilosity and coloration. As a result of this situation, the internal phylogeny of the clade is far from being properly understood and, due to our incapacity to detect sufficient, plausible synapomorphies, the internal phylogeny of this clade should be considered as tentative.

laminatus clade

 * Cephalotes christopherseni
 * Cephalotes duckei
 * Cephalotes inaequalis
 * Cephalotes laminatus
 * Cephalotes minutus
 * Cephalotes simillimus
 * Cephalotes spinosus

A medium size clade containing seven Recent species characterised by the following synapomorphies: vertexal angles of the worker with a truncate lamella and gyne with four coloured spots on the gaster, a character which appears to have been secondarily lost in christopherseni; in this species the four coloured gastral spots are still visible as an undifferentiated macula in some specimens. Most species of the clade appear to be restricted to the S American rain forest with the remarkable exception represented by minutus which is one of the commonest and most broadly distributed species of the genus. This clade corresponds roughly to Kempf (1951) "spinosus group" with his 1974 addition of duckei.

multispinosus clade

 * Cephalotes biguttatus
 * Cephalotes goniodontus
 * Cephalotes hispaniolicus
 * Cephalotes multispinosus
 * Cephalotes poinari
 * Cephalotes squamosus

This clade is characterised by only one synapomorphy: the reduced propodeal lamella. It comprises a Mexican and two Dominican fossils and three Recent Mesoamerican species. The outgroup of the clade is the clypeatus clade. It is remarkable that the first species of the multispinosus clade (poinari) still exhibits the general habitus of the members of the clypeatus clade though missing three of the four synapomorphies of it. The fourth synapomorphy of the clypeatus clade (CI > 155) is present also in poinari but it results homoplastic with the one of the clypeatus clade under any customary assumption on character evolution. Kempf (1951) supposed that biguttatus and "multispinosus" (= goniodontus) represent a distinct subgroup of his pavonii-group. Our cladogram suggests a paraphyletic position for biguttatus and multispinosus as compared with the pavonii clade. This forces us to regard these two species plus one Recent and three fossil ones closely related to them as a separate clade sharing with the species of the pavonii clade and with Cephalotes umbraculatus (the unique member of its own clade) the angle between the basal and declivous faces of the propodeum ≥ 110°.

pinelii clade

 * Cephalotes caribicus
 * Cephalotes incertus
 * Cephalotes kukulcan
 * Cephalotes liepini
 * Cephalotes maculatus
 * Cephalotes nilpiei
 * Cephalotes pileini
 * Cephalotes pinelii
 * Cephalotes scutulatus

pusillus clade

 * Cephalotes columbicus
 * Cephalotes pusillus

The two species constituting this clade have been considered as only one (pusillus) by Kempf (1951). Pusillus was regarded by Kempf (1.c.) as a member of his "spinosus species group" which is roughly equivalent to our laminatus clade and with which it shares several characters. In our analysis pusillus and columbicus result separate and paraphyletic respect to the laminatus clade. The main reason for this is the presence of fine reticulation under the head, a character present in Cephalotes solidus and in all the members of the laminatus clade but absent in pusillus and columbicus. Another character separating pusillus and columbicus from the members of the laminatus clade (absence of angulate femora in the former vs. presence in the latter) is actually present only in the basal species of the laminatus clade and absent in the internal ones. The synapomorphies of the pusillus clade resulting from our phylogenetic reconstruction are the following:

1. Frontal carinae of the soldier not reaching the vertex. This character is present also in some ingroup species of the laminatus clade.

2. Aedeagus with long spines hidden by the basal projection.

3. Internal face of the aedeagus ventrally concave.

We are inclined to recognise a significant phylogenetic value to characters 2 and 3. The crucial fact forcing the distinction between the pusillus clade and the laminatus clade, however, is the position of the insufficiently known species solidus (q. v.) - intermediate between the two clades in our Cephalotes phylogeny. This position may be subject to change after discovery of the solidus soldier, gyne and male.

solidus clade
Cephalotes solidus

This clade contains a single species known from five workers only. Several important male, gyne and soldier characters remain unknown and we may expect the phylogenetic position of this species to be subject to considerable change once soldiers, gynes and males will be discovered. The sole apomorphy of the clade resulting from our data matrix is the propodeum with basal and declivous faces not separate by a spine, a character state common to all most specialized species of the genus and regularly absent in the clades topologicaly closer to solidus. Other autapomorphies of solidus that we consider of lesser importance are listed under the species' treatment. Kempf (1974) considered solidus as a member of his (1958a) "angustus group", corresponding grosso modo to the three terminal clades of our phylogeny. All members of the "angustus group" (and other species as well) exhibit the same propodeal morphology as solidus and confirm, in this way, Kempf's intuitive placement of this species. In addition, most critical synapomorphies for the clade better corresponding to Kempf's "angustus group" in our phylogeny are soldier or gyne characters, i. e. characters unknown in C. solidus. Solidus, however, lacks a number of worker synapomorphies of different hierarchic level regularly present among most members of the "angustus group". The most significant ones are probably characters 39-42 state 1 (solidus = 0).

By means of the Constraints command of Paup we forced solidus to into a clade corresponding to Kempf’s "angustus group". All 14 resulting possible optimal trees are only two steps longer than our phylogeny of Fig. 24. The position of solidus is constant in all 14 trees: it results as the outgroup species of all the other members of Kempf's "angustus group".

umbraculatus clade
Cephalotes umbraculatus

As already intuitively proposed by Emery (1922) and by Kempf (1958) this is a very distinctive clade containing only one species characterised by the following five autapomorphies: characters 8: 0->2, 50: 0->1, 108: 0->1, 118: 0->1, 126: 0->1. In spite of the resulting isolate status within the Cephalotes phylogeny, umbraculatus shows some characters clearly intermediate between its most adjacent clades as listed under the discussion of the species. Umbraculatus appears to be one of the commonest species of the genus in large parts of the Neotropical rain forests.

wheeleri clade

 * Cephalotes hirsutus
 * Cephalotes insularis
 * Cephalotes rohweri
 * Cephalotes toltecus
 * Cephalotes wheeleri

A small clade containing only 5, very distinctive, species, all restricted to a broad Sinaloan-Sonoran region from Arizona to the states of Jalisco and Morelos to the south and including Las Islas de Tres Marias. These species are easily recognizable and, in our cladogram, they are characterised by a set of six synapomorphies: for the workers, (1) the postoccipital suture extending over the ventral side of the head, (2) the first gastral tergite striate, (3) the loss of gastral coloured spots, (4) the presence of erect, truncate hairs, and, for the soldiers, (5) the antennal scrobes terminating below the eyes, and, for the gynes, (6) loss of the gastral coloured spots (a trait not necessarily correlated with the analogous one of workers). In spite of their compact phylogenetic robustness and unequivocal presence of advanced synapomorphies (soldiers and gynes with disc, etc.), the workers of the species of this clade bear a strong, superficial similarity with the basalmost Cephalotes clade: the hamulus clade.