Stigmatomma Roger 1859

Esteves, Flavia A. & Fisher, Brian L., 2016, Taxonomic revision of Stigmatomma Roger (Hymenoptera: Formicidae) in the Malagasy region, Biodiversity Data Journal 4, pp. 8032-8032 : 8032

Stigmatomma Roger 1859

Stigmatomma as junior synonym of Amblyopone : Emery and Forel 1879: 455; Mayr 1887: 546. Revived from synonymy: Dalla Torre 1893: 14. Subgenus of Amblyopone : Forel 1900: 55; Clark 1934: 27; Brown 1949: 87. Revived status as genus: Bingham 1903: 36; Emery 1911: 23; Creighton 1950: 31. Junior synonym of Amblyopone : Brown 1960: 155. Revived status as genus: Yoshimura and Fisher 2012b: 17. Senior synonym of Arotropus : Yoshimura and Fisher 2012b: 17.

Stigmatomma = Arotropus Provancher 1881: 205. Type-species: Arotropus binodosus (junior synonym of Typhlopone pallipes ), by monotypy.

Stigmatomma Stigmatomma denticulatum Roger 1859 Bingham 1903: 36. by subsequent designation

Diagnosis

Workers of Stigmatomma in the Malagasy bioregion - characters of the Amblyoponinae as described by Brown (1960) and the following characters:

Mandible elongate and linear, not as long as the head, pointed at the apex (Fig. 11). Masticatory and basal margins running parallel to each other along baso-apical axis, resulting in two rows of teeth (Fig. 12). Teeth of the same pair generally basally fused.

Median portion of clypeal anterior margin anteriorly projected (generally convex; Fig. 11). Anterior clypeal margin armed with single row of dentiform setae, arising from tubercle--like cuticular projections or from the flat cuticle (Fig. 12). Pair of long setae on clypeus, generally arising from its anterior margin.

Genal teeth present or absent.

Number of antennomeres: 10-12.

Under the stereomicroscope, pilosity similar present on all antennomeres (Fig. 11).

Palpal formula: 4:3; 4:2; or 2:2 (two maxillary and two labial).

Metanotal suture well developed to absent.

Mesepisternum generally divided into anepisternum and katepisternum (Fig. 2).

Number of mesotibial spurs: 0-2.

Anterodorsal face of mesobasitarsus generally with a longitudinal sulcus (Fig. 3b).

Number of metatibial spurs: 1-2.

Anterior face of metabasitarsus generally without a longitudinal sulcus.

Pretarsal claw simple; arolium present on pro-, meso-, and metapretarsi (Fig. 3d).

Petiole (abdominal segment II) sessile (Fig. 13). Subpetiolar process present; fenestra present or absent on its lateral face.

Constriction, generally scrobiculate, present between pretergite and postergite of abdominal segment III.

Prora present.

Scrobiculate constriction present between presclerites and postsclerites of abdominal segment IV.

Stout spiniform setae on apex of hypopygium present or absent (Fig. 14).

Comments on worker characters

The list of characters above forms an inclusive diagnosis of the genus, but no character can currently be pointed as unique for Stigmatomma .

1. In Stigmatomma , the total dental count (including teeth arranged in pairs) recorded for Malagasy species is 11-15, distributed from base to apex as follows: 1-3 single teeth, followed by 3-6 teeth pairs (generally fused at the base), a pre-apical (generally single) tooth, and an apical pointy tooth (Fig. 12). Tooth number and arrangement may be constant within some species, but not for all species we evaluated: it varies within nest series and even between left and right mandibles of the same specimen. Given that, we did not use these characters alone to isolate individual species.

The most basal tooth is enlarged in the majority of species we studied, but not in all (Fig. 12). This contradicts the opinion of Yoshimura and Fisher (2012b), which is that all Malagasy Stigmatomma species possess an enlarged basal tooth in their mandibles.

Teeth coupling generally occurs between teeth with similar dimensions (Fig. 12a). However, in two species ( Stigmatomma bolabola sp. n. and S. sakalava sp. n.), dorsal teeth increase in size towards the mandible’s apex (Fig. 15). In that case, the dorsal tooth is smaller than the ventral paired tooth, but at the mandible's apex. This also contradicts Yoshimura and Fisher (2014) and Yoshimura and Fisher (2012b), who were of the opinion that dorsal teeth are smaller than ventral teeth in the XMMAS clade genera. In their view, the genus Amblyopone would generally present mandibles with no teeth pairs, but if teeth were present, the dorsal tooth would be larger than the respective ventral pair. A species noteworthy in this discussion is Stigmatomma pluto ( Gotwald and Lévieux 1972) (ANTWEB1008502; Afrotropical region), whose mandible has no basal teeth paired with mandibular teeth, thus resembling the mandible of Amblyopone (Fig. 16).

Among the other Amblyoponinae genera distributed in the Malagasy bioregion: Prionopelta has short and subtriangular mandibles, which are usually armed with three teeth on the apical half, so that basal and mastigatory margins are distinct (Fig. 17c). The mandibles of Mystrium are similar to those of Stigmatomma in their indistinct basal and mastigatory margins, but are longer than its head, and have blunt apex ( Bolton 1994; Fig. 17b). Also in Mystrium , the ventral row of teeth is set far apart from the dorsal row ( Yoshimura and Fisher 2014). Adetomyrma and Xymmer , like Stigmatomma , present mandibles that shorter than the head, with indistinct basal and masticatory margins and a pointy apex (Fig. 17a, d). While teeth are not disposed in pairs along the mandibles of Adetomyrma ( Yoshimura and Fisher 2012b), the mandibles of Xymmer do have pairs of teeth.

In addition to the similarities and differences among the shape and configuration of the mandibles, an enlarged mandibular basal tooth is absent in all other Malagasy Amblyoponinae genera ( Yoshimura and Fisher 2012a, Yoshimura and Fisher 2012b; Fig. 17).

2. Number and configuration of clypeal cuticular processes and associated dentiform setae vary among the evaluated species of Stigmatomma . All species present three to ten cuticular processes on the anterior margin of the clypeus. Each medial process bears one dentiform seta.

In half of the species ( tsyhady species-complex members and Stigmatomma janovitsika sp. n.), the seta on the lateral-most process is laterodistally followed by a row of dentiform setae. These lateral rows extend laterad on the anterior clypeal margin, where it arises from flat cuticle (Fig. 12a). In few species ( S. bolabola sp. n. and S. sakalava sp. n.), the lateral-most cuticular process is smaller, and does not bear any dentiform setae (Fig. 15). S. besucheti presents three medial cuticular processes that are followed laterodistally by a notch on the anterior clypeal margin. This notch is succeeded by a row of dentiform setae arising from flat cuticle (or from reduced cuticular processes; Fig. 12b).

However, the number of medial cuticular processes may vary within some species and sometimes within nest series. Thus, we did not use such variations to isolate individual species.

Among the other Amblyoponinae genera present in the Malagasy region, Mystrium , like Stigmatomma , also presents a single row of cuticular projections bearing dentiform setae on the anterior clypeal margin (Fig. 17b; or see ANTWEB1008554 for high-magnification images). On the other hand, Xymmer has neither specialized setae nor cuticular tubercle--like projections (Fig. 17d; or see ANTWEB1008499 for more images); in Adetomyrma , all dentiform clypeal setae arise from flat cuticle (Fig. 17a; or see ANTWEB1008494 for SEM images); and Prionopelta seems to have cuticular projections welded onto an anterior clypeal apron (Fig. 17c).

A pair of long setae is present on the anterior margin of the clypeus of all genera in the XMMAS clade in the Malagasy region, however, they are reduced and stouter in Mystrium (CASENT0002095).

3. The presence or absence of genal teeth is uniform within Stigmatomma species, and this character has relative importance to group species with similar morphology. In the Malagasy bioregion, this trait is present in all Mystrium species (Fig. 17b) and absent in Adetomyrma (Fig. 17a), Prionopelta (Fig. 17c), and Xymmer (Fig. 17d).

4. Despite the variation among species, the number of antennomeres is constant within the Stigmatomma species we studied. Adetomyrma , Mystrium , and Xymmer species present no variation for this character, with all having twelve- antennomeres.

5. Under the stereomicroscope, the whole antenna is equally covered by setae in Adetomyrma , Prionopelta , Stigmatomma , and Xymmer (Figs 11, 17a, c, d). In Mystrium , the four apical-most antennomeres are covered with denser pilosity (Fig. 17b). SEM images show that the apical antennomeres in Mystrium are actually covered by a different type of setae (ANTWEB1008554).

6. Without dissection, the maxillary and labial palpomeres are often extremely difficult to count in the species we studied.

Regarding the number of maxillary and labial palpomeres in other Amblyoponinae members in the Malagasy region, the palpal formula is constant within Mystrium (4:3) and Prionopelta (2:2) ( Yoshimura and Fisher 2014), but not in Adetomyrma and Xymmer .

The palpal formula published for the Adetomyrma worker caste is 3:3, but some species are only known by the male caste, which, depending on the species, may present palpomere counts of 2:2 and 2:3 ( Yoshimura and Fisher 2012a). The palpal formula for Xymmer males is 4:3/3:3/3:2 ( Yoshimura and Fisher 2012b). Since published records indicate that the number of palpomeres is generally constant across castes of Amblyponinae species ( Brown 1960), we expect the females of Xymmer and Adetomyrma to reflect a similarly diverse combination.

Finally, Yoshimura and Fisher (2012b) presented 4:3/4:2/3:3 as palpal formula for Stigmatomma males in the Malagasy region, differing from the numbers we counted for workers. However, mouthpart dissections on several male specimens of the same morphotypes used by Yoshimura & Fisher revealed that, for Stigmatomma , the number of palpomeres is the same in males and females (4:3/4:2; not evaluated for S. besucheti , as males are unknown).

7. The presence or absence of the metanotal suture, and the degree of its impression, may vary within species, as well as within nest series of Stigmatomma in the Malagasy region. Given this, we did not use those variations to isolate individual species.

9. The number of mesotibial spur(s) is difficult to determine under stereomicroscopes when the anterior spur is reduced in size, and also because the posterior spur may be “replaced” by an enlarged, stout spiniform seta. SEM images allowed comparisons between the texture of enlarged spinifom processes and surrounding cuticle, thus enabling us to differentiate spur and seta (Fig. 18).

In the Stigmatomma we studied, the number of mesotibial spurs ranged from zero to two, and were generally constant within species. In one species, S. liebe sp. n., the number of mesotibial spurs visible under the stereomicroscope ranges from one to two. The anterior spur may be visible and developed, but it is vestigial in the majority of the specimens we evaluated. This variation was observed in specimens from the same nest series.

Regarding other members of the XMMAS clade, Stigmatomma pallipes (ANTWEB1008501; Nearctic region), S. pluto (ANTWEB1008502), Adetomyrma caputleae Yoshimura and Fisher 2012a (ANTWEB1008494; Malagasy region), Fulakora mystriops ( Brown 1960) (ANTWEB1008500; Neotropical region), Myopopone castanea ( Smith 1860) (ANTWEB1008551; Indomalaya and Australasia regions), and Xymmer muticus Santschi 1914 (ANTWEB1008499; Afrotropical region) have two mesotibial spurs. A. venatrix Ward 1994 (Malagasy region) possesses one spur ( Ward 1994), as well as F. chilensis ( Mayr 1887) (ANTWEB1008496; Neotropical region) and Mystrium voeltzkowi Forel 1897 (ANTWEB1008554; Malagasy region). All Xymmer morphospecies from Madagascar evaluated under a stereomicroscope presented one spur/stout seta on the apex of the mesotibia. One species clearly seems to have a spur, while the others apparently present an enlarged stout seta.

Among the Amblyoponinae genera outside the XMMAS clade, Amblyopone australis Erichson 1842 (ANTWEB1008497; Australasia region), A. mercovichi Brown 1960 (ANTWEB1008498; Australasia region), and Apomyrma stygia Brown et al. 1971 (ANTWEB1008505) possess two mesotibial spurs. Onychomyrmexdoddi Wheeler 1916 (ANTWEB1008560; Australasia region) possesses two vestigial spurs at the apex of the mesotibia. Each spur is a small, stout, conic seta totally or partially concealed by a fovea. Prionopelta aethiopica Arnold 1949 (ANTWEB1008580; Afrotropical region) and P. antillana Forel 1909 (ANTWEB1008581; Neotropical region) have one vestigial spur, while P. concenta ( Brown 1974) (ANTWEB1008513; Afrotropical region) presents no spurs on the mesotibia.

10. We confirm the presence of a longitudinal sulcus on the antero-dorsal face of the mesobasitarsus in all species of Stigmatomma in the Malagasy region save S. tsyhady sp. n.

Within the XMMAS clade, this sulcus is present on the mesobasitarsus of Stigmatomma pallipes (ANTWEB1008501), S. pluto (ANTWEB1008502), Adetomyrma caputleae (ANTWEB1008494), Fulakora chilensis (ANTWEB1008496), F. mystriops (ANTWEB1008500), Myopopone castanea (ANTWEB1008551), and Xymmer muticus (ANTWEB1008499). We confirm present of this sulcus in only one Xymmer species in the Malagasy region. However, this character is difficult to visualize under a stereomicroscope when specimens are too small, as it occurs with Xymmer species, and its presence or absence may be better evaluated with an SEM microscope. This sulcus is absent in all Mystrium species we evaluated in the Malagasy region (CASENT0429914; CASENT0482698; CASENT0003281; CASENT0429897; CASENT0129838; CASENT0418314; CASENT0318933; CASENT0494274; CASENT0248701; CASENT0001158; ANTWEB1008554).

The sulcus on the anterior face of the mesobasitarsus is absent in Amblyopone australis (ANTWEB1008497), A. mercovichi (ANTWEB1008498), Apomyrma stygia (ANTWEB1008505), Onychomyrmex doddi (ANTWEB1008560), Prionopelta aethiopica (ANTWEB1008580), P. antillana (ANTWEB1008581), and P. concenta (ANTWEB1008513).

11. All Stigmatomma species present in the Malagasy bioregion present two well-developed metatibial spurs save S. liebe sp. n. In this species, the number of metatibial spurs visible under the stereomicroscope ranges from one to two. The anterior spur is visibly smaller than the posterior spur, and may be vestigial in some specimens. This variation was observed in specimens from the same nest series. A similar condition is found in Onychomyrmex hedleyi Emery 1895 (Australasia region). In this species, metatibial spurs are vestigial and may be present or absent in specimens from the same colony ( Brown 1960).

In the XMMAS clade, Stigmatomma pallipes (ANTWEB1008501), S. pluto (ANTWEB1008502), Adetomyrma caputleae (ANTWEB1008494), A. venatrix , Fulakora chilensis (ANTWEB1008496), F. mystriops (ANTWEB1008500), Myopopone castanea (ANTWEB1008551), Mystrium voeltzkowi (ANTWEB1008554), and Xymmer muticus (ANTWEB1008499) possess two spurs on the metatibia.

Amblyopone australis (ANTWEB1008497), A. mercovichi (ANTWEB1008498), and Apomyrma stygia (ANTWEB1008505) possess two metatibial spurs. Onychomyrmex doddi (ANTWEB1008560) possesses two vestigial spurs at the apex of the metatibia. These spurs are small, stout, conic seta totally or partially concealed by a fovea. Prionopelta aethiopica (ANTWEB1008580) and P. antillana (ANTWEB1008581) have one spur, while P. concenta (ANTWEB1008513) presents no spurs.

12. Only one Stigmatomma species evaluated in this study ( S. roahady sp. n.) presents a longitudinal sulcus on the anterior face of the metabasitarsus. The metabasitarsus of S. besucheti , while not presenting a sulcus on its anterior face, possesses two raised, parallel, not--well--developed longitudinal carinae with convergent apexes on its dorsal face.

This sulcus is present on the metabasitarsus of Myopopone castanea (ANTWEB1008551), and absent in Stigmatomma pallipes (ANTWEB1008501), S. pluto (ANTWEB1008502), Adetomyrma caputleae (ANTWEB1008494), A. venatrix , Fulakora chilensis (ANTWEB1008496), F. mystriops (ANTWEB1008500), and Xymmer muticus (ANTWEB1008499). It seems to be absent on the metabasitarsus of Xymmer in the Malagasy region. However, we cautiously affirm that, since this character is difficult to visualize under a stereomicroscope when specimens are too small, like those of Xymmer , it would be better evaluated under higher magnification. This sulcus is absent in all Mystrium species we evaluated in the Malagasy bioregion (CASENT0429914; CASENT0482698; CASENT0003281; CASENT0429897; CASENT0129838; CASENT0418314; CASENT0318933; CASENT0494274; CASENT0248701; CASENT0001158; ANTWEB1008554).

Among the Amblyoponinae genera that are not part of the XMMAS clade, the sulcus on the metabasitarsus is absent on Amblyopone australis (ANTWEB1008497), A. mercovichi (ANTWEB1008498), Apomyrma stygia (ANTWEB1008505), Onychomyrmex doddi (ANTWEB1008560), Prionopelta aethiopica (ANTWEB1008580), P. antillana (ANTWEB1008581), and P. concenta (ANTWEB1008513).

13. Arolium present on pro-, meso-, and metapretarsi in all species we studied. The same seems to apply to the other Amblyoponinae genera in the Malagasy region.

14. The petiole is sessile to sub-sessile in Adetomyrma and Mystrium ; and subsessile to penduculate in Xymmer (Fig. 19). Also, within the XMMAS clade in the Malagasy region, Xymmer is the only genus in which the subpetiolar process is absent.

15. The constriction between pretergite and postergite of the abdominal segment III is scrobiculate in all Stigmatomma species but one. In Adetomyrma such a constriction is not visible; in Xymmer species the constriction is alveolate; and in Mystrium it is scrobiculate.

16. A prora is visible under a stereomicroscope in all Stigmatomma and Mystrium species in the Malagasy region; it seems to be absent in Adetomyrma and Xymmer .

17. Adetomyrma does not possess a constriction between the presclerite and postsclerite of abdominal segment IV. The constriction is scrobiculate in Mystrium and Stigmatomma , and alveolate in Xymmer .

18. Stout spiniform setae may be located on the apex of the hypopygium, surrounding the sting (Fig. 14). The number of setae varies from six to nine, when present in Stigmatomma species in the Malagasy region. This contradicts the opinion of Yoshimura and Fisher (2014), which states that the number of stout setae ranges from three to nine.

In the Malagasy region, all Mystrium species present two or four stout setae on the hypopygium ( Yoshimura and Fisher 2014), while Xymmer and Adetomyrma have no such setae. Yoshimura and Fisher (2014) affirmed that two or four stout setae on the apex of the hypopygium are uniquely observed in Mystrium ; however, Fulakora mystriops (ANTWEB1008500) also presents four stout setae on the hypopygium.

Stout spiniform setae are also present on the hypopygium of Stigmatomma pluto (twelve setae, ANTWEB1008502), Fulakora chilensis (eight setae, ANTWEB1008496), and in F. cleae ( Lacau and Delabie 2002) and F. agostii ( Lacau and Delabie 2002), which have ten setae each (both from the Neotropical region). These setae are absent in S. pallipes (ANTWEB1008501), the Neotropical F. heraldoi ( Lacau and Delabie 2002), Myopopone castanea (ANTWEB1008551), Xymmer muticus (ANTWEB1008499), Amblyopone australis (ANTWEB1008497), A. mercovichi (ANTWEB1008498), Apomyrma stygia (ANTWEB1008505), Onychomyrmex doddi (ANTWEB1008560), Prionopelta aethiopica (ANTWEB1008580), and P. concenta (ANTWEB1008513).

Malagasy species-group Stigmatomma

We introduce a morphological organization system for the species diversity of Stigmatomma in the Malagasy bioregion which is based upon the definition of informal species-groups, which may contain species-complexes when necessary. Groups and complexes are named after the most abundant species, and the groups we presently define only reflect what is seen in the Malagasy fauna.

Synoptic list of Malagasy species

besucheti group

besucheti (Baroni Urbani 1978) (Seychelles; Singapore?)

tsyhady group

sakalava complex

bolabola Esteves & Fisher sp. n. (Madagascar)

janovitsika Esteves & Fisher sp. n. (Seychelles)

sakalava Esteves & Fisher sp. n. (Madagascar)

tsyhady complex

irayhady Esteves & Fisher sp. n. (Madagascar)

liebe Esteves & Fisher sp. n. (Madagascar)

roahady Esteves & Fisher sp. n. (Madagascar)

tsyhady Esteves & Fisher sp. n. (Madagascar)

besucheti species-group

Stigmatomma besucheti ( Baroni Urbani 1978)

The morphology of S. besucheti isolates the species from other Stigmatomma in the Malagasy bioregion, and we place it in its own group based on the following worker characters (asterisks flag unique characters within the genus in the Malagasy bioregion):

1. * Ten antennomeres;

2. * Two maxillary palpomeres (palpal formula: 2:2);

3. * Calcar of strigil completely pectinate;

4. * Anterior face of the calcar of strigil with squamiform microtrichia basally;

5. * Posterior face of the calcar of strigil glabrous;

6. * Weakly raised longitudinal parallel carinae present on the dorsal face of metabasitarsus, with convergent apexes;

7. * Petiolar proprioceptor zone reduced to a small concavity.

tsyhady species-group

Workers with the following combination of characters (asterisks flag unique characters within the genus in the Malagasy bioregion):

1. * Twelve antennomeres;

2. * Four maxillary palpomeres (palpal formula: 4:3 or 4:2);

3. * Calcar of strigil not completely pectinate; baso-ventral lamella generally visible (in one species the lamella is reduced to a basal bud);

4. Anterior face of the calcar of strigil with strap-like or tubiform microtrichia basally;

5. * Posterior face of the calcar of strigil with lanceolate microtrichia;

6. Absence of any longitudinal carina on the dorsal face of metabasitarsus;

7. * Petiolar proprioceptor zone a large, round concavity.

This group can be split into subgroups based on morphological similarities, here called species complexes.

sakalava species-complex

Stigmatomma bolabola Esteves & Fisher, sp. n.

Stigmatomma janovitsika Esteves & Fisher, sp. n.

Stigmatomma sakalava Esteves & Fisher, sp. n.

Workers with the following combination of characters (character numbers are sequential to the species groups for sake of clarity in the character discussion):

8. Genal teeth present or absent;

9. Two labial palpomeres (palpal formula: 4:2);

10. Antler--like microtrichia present on posterior face of posterior metatibial spur;

11. Absence of fenestra on the subpetiolar process;

12. Stout spiniform setae present on the apex of hypopygium.

tsyhady species-complex

Stigmatomma irayhady Esteves & Fisher, sp. n.

Stigmatomma liebe Esteves & Fisher, sp. n.

Stigmatomma roahady Esteves & Fisher, sp. n.

Stigmatomma tsyhady Esteves & Fisher, sp. n.

Workers with the following combination of characters (character numbers are sequential to the species groups for sake of clarity in the character discussion; asterisks flag unique characters within the genus in the Malagasy bioregion):

8. Genal teeth present;

9. * Three labial palpomeres (palpal formula: 4:3);

10. Posterior face of posterior metatibial spur mostly glabrous;

11. * Fenestra present on the subpetiolar process;

12. * Absence of stout spiniform setae on hypopygium.

Comments on species-groups and species-complexes characters

3. A reduced lamella on the baso-ventral margin of the calcar of strigil is often difficult to visualize under a stereomicroscope, and the calcar may appear completely pectinate while in reality it has a basal bud on the base of its ventral margin. Nonetheless, the proportion of lamellar tissue on the ventral margin of the calcar is constant within species, and was helpful to delimit certain species.

4-5. Presence and shape of microtrichia on anterior and posterior face of the calcar of strigil are not visible under a stereomicroscope. However, those characters are informative to diagnose groups of species.

6. The longitudinal parallel carinae on the dorsal face of the Stigmatomma besucheti metabasitarsus somewhat converge at their apexes; thus, the region between them appears groove-like in dorsal view. No other species of Stigmatomma in the Malagasy region presents such a character. However, one species, S. roahady , possesses a longitudinal sulcus on the anterior face of its metabasitarsus, and since its shape and location are different from the carinae on S. besucheti , we did not consider them homologous.

10. The presence and shape of microtrichia on the posterior face of the metatibial spur are not visible under a steromicroscope; however, it is informative to diagnose groups of species.