Tetramorium tortuosum

Hita Garcia, F. & B. L. Fisher, 2012, The ant genus Tetramorium Mayr (Hymenoptera: Formicidae) in the Malagasy region - taxonomic revision of the T. kelleri and T. tortuosum species groups., Zootaxa 3592, pp. 1-85 : 14-20

Tetramorium tortuosum species group

Diagnosis

Eleven-segmented antennae; anterior clypeal margin medially impressed; frontal carinae well-developed and usually running to posterior head margin; anterior face of mesosoma weakly developed; margination between lateral and dorsal mesosoma generally well-developed; propodeal spines always long to extremely long, spinose, and acute (PSLI 28-72); propodeal lobes usually well-developed, triangular to elongate-triangular, generally short and acute, rarely strongly reduced to almost absent; petiolar node rectangular nodiform, anterodorsal and posterodorsal margins usually well-defined, anterior and posterior faces often parallel, node longer than wide in most species, broader than long in few species; postpetiole usually globular to subglobular; mandibles strongly sculptured in most species; head and mesosoma with distinct and predominantly longitudinally rugose sculpture; waist segments with distinctly rugose, rarely rugulose, sculpture; gaster unsculptured, smooth and shiny in many species, but sculpture present on the first gastral tergite in several species; in most species all dorsal surfaces of head, mesosoma, waist segments and gaster with abundant, long, standing hairs; sting appendage spatulate.

Comments

Within the Malagasy region, the T. tortuosum group is easily recognisable within the groups with 11-segmented antennae. The distinction from the T. kelleri group was explained in detail above. The T. plesiarum group is characterised by its distinct and conspicuous antennal scrobes with well-defined margins all-around. By contrast, the scrobes are usually developed, but less conspicuous and without well-defined posterior and ventral margins in the T. tortuosum group. Due to the presence of distinct sculpture on both waist segments, the group cannot be mistaken for the T. bessonii, T. marginatum, T. naganum, T. schaufussii, T. severini, T. tsingy, or T. weitzeckeri groups, nor parts of the T. bonibony and T. dysalum groups. The species of the T. bonibony group with sculptured waist segments have reticulate-rugose sculpture on the posterior head and anterior mesosoma which is not present in the T. tortuosum group. Most species of the T. dysalum group with sculptured waist segments usually have a weakly sculptured petiolar node which distinguishes them from the T. tortuosum group species. Tetramorium dysalum has more sculpture, and could be misidentified with T. avaratra or T. pleganon on the basis of petiolar node shape, but the latter species have sculptured mandibles and sculpture on the first gastral tergite, whereas T. dysalum possesses smooth mandibles and lacks sculpture on the first gastral tergite. Moreover, the T. ranarum group, despite sharing the rectangular nodiform shape of the petiolar node in some species, differs in several other important aspects, making it easily separable from the T. tortuosum group. The sculpture on posterior head and mesosoma is usually reticulate-rugose in the T. ranarum group but longitudinally rugose in the T. tortuosum group. Also, the propodeal spines are also much longer in the latter group than in the T. ranarum group. In addition, the frontal carinae and antennal scrobes are often much weaker in the T. ranarum group, and several species have one or even both waist segments unsculptured, whereas all Malagasy T. tortuosum group species have both waist segments noticeably sculptured.

Most Malagasy T. tortuosum group members appear to form a natural grouping except for T. avaratra and T. pleganon. In these two the petiolar node has a shape with the anterodorsal margin situated higher than the posterodorsal and the dorsum tapers distinctly backwards posteriorly, which, as mentioned above, is also seen in the T. dysalum group. The true affinities of T. avaratra and T. pleganon are unclear at the moment, and might be revealed by the use of molecular data in future studies. At present, however, we place them in the T. tortuosum group since they seem to fit best in this group until more data becomes available.

Our revision has revealed a remarkable 22 species within the T. tortuosum group, which makes it the most species-rich Tetramorium species group in the Malagasy region. In order to facilitate the work with this comparatively high number of species, we have split the group into four species complexes on the basis of few important and conspicuous morphological key characters.

Key to species of the T. tortuosum species group (workers)

1. In profile forecoxae completely covered with very distinct, strong, longitudinal rugae ( T. smaug species complex) (Fig. 11).... 2

In profile forecoxae without very distinct, strong, longitudinal rugae; usually unsculptured, smooth and shining, but often with traces of rugulae or punctate sculpture (Figs. 12, 13)..........................................................9

2. Propodeal spines long to extremely long (PSLI 34-50, generally below 45); comparatively hairy species with numerous long standing hairs on the first gastral tergite (Fig. 14)............................................................ 3

Propodeal spines always extremely long (PSLI 48-72; generally above 50); less hairy species with no or few scattered, long standing hairs (Figs. 15, 16)............................................................................. 7

3. Petiolar node with posterodorsal margin situated higher than anterodorsal, dorsum convex (Fig. 17)............. T. adamsi

Petiolar node with anterodorsal and posterodorsal margins at about the same height, dorsum flat to weakly convex (Fig. 18)...4

4. Antennal scapes comparatively long (SI 89-92); petiolar node higher (LPeI 81-88); body colour dark brown to black (Figs. 19, 20).................................................................................. Tetramorium nazgul

Antennal scapes shorter than above (SI 79-85); petiolar node lower (LPeI 89-97); body colour orange to light brown (Figs. 21, 22)................................................................................ Tetramorium marojejy

7. First gastral tergite without any standing hairs, only with moderately dense appressed pubescence (Fig. 23).................................................................................................. Tetramorium latreillei

First gastral tergite with several standing hairs and scarce pubescence (Fig. 24)..................................... 8

8. Leading edges of antennal scapes with appressed hairs; mesosoma with just one to two pairs of standing hairs on the pronotal dorsum (Figs. 25, 26).................................................................. Tetramorium sabatra

Leading edges of antennal scapes with subdecumbent to suberect hairs; mesosoma with 7 to 14 pairs of standing hairs throughout the whole mesosomal dorsum (Figs. 27, 28)............................................... Tetramorium smaug

9. First gastral tergite with either reticulate-punctate or costulate sculpture (Figs. 29, 30)..............................10

First gastral tergite unsculptured, smooth, and shining ( T. andrei species complex) (Fig. 31)..........................16 first

10.

First gastral tergite with basigastral costulae ( T. noeli species complex) (Fig. 32)................................... 11 First gastral tergite differently sculptured ( T. jedi species complex) (Fig. 33)......................................14

11. In profile view, petiolar node with anterodorsal and posterodorsal margins at about the same height, and the dorsum flat to weakly convex (Fig. 34)...............................................................................12

In profile view, petiolar node with the posterodorsal margin situated higher than the anterodorsal margin, and the dorsum convex (Fig. 35)........................................................................................13

12. Eyes comparatively moderate to large (OI 22-24); propodeal spines comparatively long (PSLI 41-45) (Figs. 36, 37)............................................................................................. Tetramorium aherni

Eyes comparatively small (OI 16-17); propodeal spines comparatively short (PSLI 27-29) (Figs. 38, 39).................................................................................................. Tetramorium singletonae

13. Head distinctly longer than wide (CI 92-95); propodeal spines extremely long but comparatively shorter than below (PSLI 38-48); postpetiole relatively higher (LPpI 68-72) and broader (DPpI 119-129) (Figs. 40, 41).......... Tetramorium noeli

Head weakly longer than wide (CI 97-98); propodeal spines extremely long but comparatively longer than above (PSLI 60-65); postpetiole relatively lower (LPpI 77-81) and narrower (DPpI 104-112) (Figs. 42, 43).... Tetramorium ambanizana

14. Petiolar node in dorsal view distinctly longer than wide (DPeI 79-85), in profile anterodorsal and posterodorsal margins at about same height; first gastral tergite completely covered with distinct reticulate-punctate sculpture (Figs. 44, 45).... T. jedi

Petiolar node in dorsal view distinctly wider than long (DPeI111-137); in profile anterodorsal margin situated higher than posterodorsal margin and dorsum tapering backwards; first gastral tergite never completely covered with distinct reticulate-punctate sculpture, generally with superficial reticulate-punctate sculpture restricted to the basal first half of the tergite (Figs. 46, 47).........15

15. Propodeal spines very long (PSLI 37-44); petiolar node relatively lower (LPeI 63-73) and narrower (DPeI 111-118); petiolar dorsum strongly rugose (Fig. 48)........................................................ Tetramorium ple ganon

Propodeal spines long, but shorter than above (PSLI 27-37, usually below 34); petiolar node relatively higher (LPeI 54-66) and broader (DPeI 126-137); petiolar dorsum weakly rugose (Fig. 49).......................... Tetramorium avaratra

16. Posterodorsal corner of petiolar node strongly protruding posteriorly (Fig. 50).................. Tetramorium andohahela

Posterodorsal corner of petiolar node not protruding posteriorly (Fig. 51).........................................17

17. Eyes very small (OI 15-16); propodeal spines long (PSLI 28-33); anterodorsal margin of petiolar node situated slightly higher than posterodorsal margin; body orange to light reddish brown in colour (Fig. 52).................. Tetramorium isectum

Character combination never as above; if eyes small, then propodeal spines very long to extremely long (Figs. 53, 54)....18

18. Petiolar node in profile comparatively high, between 1.3 to 1.6 times higher than long (LPeI 64-74); propodeal lobes strongly reduced and inconspicuous (Fig. 55)...................................................... Tetramorium electrum

Petiolar node in profile less high than above, between 1.1 times longer than high to 1.3 times higher than long (LPeI 76-105); propodeal lobes variably developed, usually conspicuous (Figs. 56, 57)..........................................19

19. Propodeal spines extremely long (PSLI 58-64) (Figs. 58, 59)..................................................20

Propodeal spines long to very long, but always significantly much shorter than above (PSLI 29-45) (Figs. 60, 61)........21

20. Mandibles unsculptured, smooth, and shining; body colour yellow (Figs. 62, 63)....................... Tetramorium elf

Mandibles noticeably longitudinally sculptured; body colour very dark brown to black (Fig. 64, 65)... Tetramorium isoelectrum

21. Petiolar node in dorsal view relatively long, always more than 1.3 times longer than wide (DPeI 72-76) (Fig. 66).. Tetramorium ala

Petiolar node in dorsal view relatively wider, always between 1.0 to approximately 1.2 times longer than wide (DPeI 82-98) (Figs. 67, 68)........................................................................................22

22. Eyes relatively small (OI 16-17); propodeal spines relatively short (PSLI 29-30) (Fig. 69).............. Tetramorium nify

Eyes always much larger (OI 19-25); propodeal spines relatively longer (PSLI 32-45) (Figs. 70, 71)..................23

23. Petiolar node with weakly defined and fairly rounded anterodorsal and posterodorsal margins; postpetiole relatively longer, longer than wide to slightly wider than long (DPpI 95-101) (Fig. 72)............................. Tetramorium voasary

Petiolar node with moderately to sharply defined anterodorsal and posterodorsal margins; postpetiole relatively wider, between 1.0 to 1.4 times wider than long (DPpI 103-136) (Fig. 73, 74)................................... Tetramorium andrei