Crematogaster (subgenus)

A nominal subgenus of Crematogaster. The group was last evaluated by Blaimer (2012). Her research and numerous published studies have greatly advanced our understanding of Crematogaster systematics. Blaimer proposed the genus should be divided into two subgenera, Crematogaster and Orthocrema. This rid the genus of thirteen subgenera that were part of an archaic classification system with numerous polyphyletic clades. The two subgenera still represent an incomplete understanding of the relationships between the species of this diverse genus. For example, the subgenus Crematogaster can be divided into two clades. Based on molecular evidence, Blaimer suggested these distinctive groups could be referred to as a “global clade” and an “Australo-Asian clade.”

Blaimer (2012) stated: The new two-subgenera system as proposed follows a deep molecular divergence event between Orthocrema and Crematogaster sensu stricto, tracing back into the Mid-Eocene (ca.40–45 Mya) when these two clades last shared a common ancestor (Blaimer, in press). Recognizing these two groups from each other on a morphological basis is fairly easily achieved, although a diagnosis of the Crematogaster sensu stricto is more problematic given the high morphological variability. An obvious further improvement to the system presented here would have been the recognition of the global Crematogaster clade and the Australo-Asian Crematogaster clade as separate subgeneric entities, as they certainly show enough molecular divergence to justify a three-subgenera-approach. I refrained from such a formal distinction since it was not possible to assign species to these groups on a morphological basis. I primarily aimed to develop a practical, ‘user-friendly’ classification. Petiole and postpetiolar characters that are useful for the distinction of Crematogaster sensu stricto and Orthocrema become hypervariable within the two sensu stricto clades and are not informative at deeper phylogenetic levels. Similar character patterns, for example the presence/absence of a median longitudinal impression on the postpetiole appear to have evolved multiple times within the genus, but the selective pressures acting on morphological evolution in Crematogaster have yet to be revealed. More biological data will need to be collected to investigate these questions.

The proposed species-groups are intended as a guideline on how to structure the large Crematogaster sensu stricto clade more finely, given the phylogenetic framework. I did not attempt to assign every species sampled within the phylogeny (or otherwise known to me) to a species-group. Many more natural groups will only become apparent when the phylogeny of the genus is extended and should thus be established sequentially as data become available. For very similar reasons, I have not yet proposed species-groups for Orthocrema. The molecular sampling for Orthocrema in Blaimer (in press) is too sparse to make predictions on species-groups, as is obvious from the overall long phylogenetic branches that separate species in this clade from each other. Finally, I conclude that the main advantage of recognizing monophyletic species-groups as suggested here is, that these present manageable subunits for taxonomic revisions. In addition, these species-groups will pose excellent subjects for (needed) comparative ecological and behavioural studies within Crematogaster.

Nomenclature

 *  CREMATOGASTER [Myrmicinae: Crematogastrini]
 * Crematogaster Lund, 1831a: 132. Type-species: Formica scutellaris, by subsequent designation of Bingham, 1903: 124.
 * ACROCOELIA [junior synonym of Crematogaster (Crematogaster)]
 * Acrocoelia Mayr, 1853a: 147. Type-species: Acrocoelia ruficeps (junior synonym of Formica scutellaris), by subsequent designation of Wheeler, W.M. 1911f: 158.
 * Acrocoelia junior synonym of Crematogaster: Mayr, 1863: 404; Wheeler, W.M. 1911f: 158; Wheeler, W.M. 1922a: 828.
 * Acrocoelia revived from synonymy as subgenus of Crematogaster: Emery, 1922e: 140.
 * Acrocoelia junior synonym of Crematogaster: Buren, 1959: 126.
 * Acrocoelia revived from synonymy as genus: Soulié, 1964: 398.
 * Acrocoelia junior synonym of Crematogaster: Brown, 1973b: 178; Blaimer 2012: 52. [The type-species of Acrocoelia and Crematogaster are synonymous, the generic synonymy is therefore absolute.]
 * ATOPOGYNE [junior synonym of Crematogaster (Crematogaster)]
 * Atopogyne Forel, 1911d: 343 [as subgenus of Crematogaster]. Type-species: Crematogaster (Atopogyne) hellenica, by subsequent designation of Wheeler, W.M. 1911f: 159.
 * [Type-species not Crematogaster depressa, unjustified subsequent designation by Emery, 1912d: 272; this error repeated in Emery, 1922e: 154 and in Soulié, 1965: 78.]
 * Atopogyne raised to genus: Soulié, 1964: 398.
 * Atopogyne junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Atopogyne subgenus of Crematogaster: Bolton, 1995b: 21.
 * Atopogyne junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * COLOBOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Colobocrema Wheeler, W.M. 1927f: 31 [as subgenus of Crematogaster]. Type-species: Crematogaster (Colobocrema) cylindriceps, by monotypy.
 * Colobocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Colobocrema subgenus of Crematogaster: Bolton, 1995b: 24.
 * Colobocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * DECACREMA [junior synonym of Crematogaster (Crematogaster)]
 * Decacrema Forel, 1910a: 18 [as subgenus of Crematogaster]. Type-species: Crematogaster schencki, by subsequent designation of Wheeler, W.M. 1911f: 161.
 * [Decacrema also described as new by Forel, 1910f: 9.]
 * Decacrema raised to genus: Soulié, 1964: 398.
 * Decacrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Decacema subgenus of Crematogaster: Bolton, 1995b: 26.
 * Decacema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 52.
 * [ Decracrema Arnold, 1920a: 547, incorrect subsequent spelling.]
 * NEMATOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Nematocrema Santschi, 1918d: 182 [as subgenus of Crematogaster]. Type-species: Crematogaster stadelmanni, by original designation.
 * Nematocrema raised to genus: Soulié, 1964: 398.
 * Nematocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Nematocrema subgenus of Crematogaster: Bolton, 1995b: 38.
 * Nematocrema junior synonym of Oxygyne: Blaimer, 2012: 249.
 * Nematocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * OXYGYNE [junior synonym of Crematogaster (Crematogaster)]
 * Oxygyne Forel, 1901e: 375 [as subgenus of Crematogaster]. Type-species: Crematogaster (Oxygyne) daisyi, by subsequent designation of Wheeler, W.M. 1911f: 169.
 * Oxygyne raised to genus: Soulié, 1964: 398.
 * Oxygyne junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Oxygyne subgenus of Crematogaster: Bolton, 1995b: 40.
 * Oxygyne senior synonym of Nematocrema: Blaimer, 2012: 249.
 * Oxygyne junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 52.
 * PARACREMA [junior synonym of Crematogaster (Crematogaster)]
 * Paracrema Santschi, 1918d: 182 [as subgenus of Crematogaster]. Type-species: Crematogaster spengeli, by original designation.
 * Paracrema raised to genus: Soulié, 1964: 398.
 * Paracrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Paracrema subgenus of Crematogaster: Bolton, 1995b: 41.
 * Paracrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * PHYSOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Physocrema Forel, 1912f: 220 [as subgenus of Crematogaster]. Type-species: Crematogaster inflata, by subsequent designation of Wheeler, W.M. 1913a: 82.
 * Physocrema raised to genus: Soulié, 1964: 398.
 * Physocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Physocrema subgenus of Crematogaster: Bolton, 1995b: 42.
 * Physocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * SPHAEROCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Sphaerocrema Santschi, 1918d: 182 [as subgenus of Crematogaster]. Type-species: Crematogaster kneri, by original designation.
 * Sphaerocrema raised to genus: Soulié, 1964: 398.
 * Sphaerocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Sphaerocrema subgenus of Crematogaster: Bolton, 1995b: 46.
 * Sphaerocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.
 * XIPHOCREMA [junior synonym of Crematogaster (Crematogaster)]
 * Xiphocrema Forel, 1913k: 80 [as subgenus of Crematogaster]. Type-species: Crematogaster tetracantha, by subsequent designation of Emery, 1922e: 138.
 * Xiphocrema raised to genus: Soulié, 1964: 398.
 * Xiphocrema junior synonym of Crematogaster: Hölldobler & Wilson, 1990: 13.
 * Xiphocrema subgenus of Crematogaster: Bolton, 1995b: 50.
 * Xiphocrema junior synonym of Crematogaster (Crematogaster): Blaimer 2012: 53.

Blaimer (2012) provides the following diagnostic definition for this globally distributed subgenus:

1. Petiole shape (in dorsal view) highly variable: moderately flared (Fig. 14a), broadly flared (Fig. 15a), sharply flared (Fig.16a), greatly flared (Fig. 17a), oval (Fig. 18a) or suboval (Fig. 19a), elongate rectangular (Fig. 20), circular (Fig. 21a), or hexagonal (Fig. 22a), but not rectangular or ovo-rectangular (as in Fig. 3 or 4). If petiole elongate-rectangular (Fig. 20) and thus similar to some Orthocrema species (as in Fig. 5), then propodeal spiracle compressed oval.

2. Petiole with dorsoposterior denticles/tubercules and dorsoposterior erect setae (e.g. Figs 14a, 16a) or lacking denticles/tubercules (e.g. Figs 15a, 18a–19a, 20, 22a), while setae may still be present.

3. Postpetiole varying from distinctly (Figs 16b-17b, 19b, 22b) to weakly bilobed (Figs 14b–15b, 18b), with a broad (Fig. 16b) to thin median longitudinal impression (Fig. 23). More rarely postpetiole only with faint posterior impression (Figs 18b, 25) or lacking impression entirely (Fig. 24). Probably ~80% of the species diversity in this clade has a clearly bilobed postpetiole with a distinct median longitudinal impression.

4. Propodeal spiracle often oval or compressed oval (Fig. 26).

5. Occipital carinae variable, but often reduced (Fig. 27).

6. Antennae usually 11-segmented, rarely 10-segmented or (one species) 9-segmented. Antennal scapes of variable length; if antennae distinctly clubbed, then usually club 3-segmented.

7. Head shape highly variable, but often with a straight (Fig. 28) or medially depressed posterior head margin (Fig. 29) and with suboval or subangular corners.