Royidris, Bolton & Fisher, 2014

Bolton, Barry & Fisher, Brian, 2014, The Madagascan endemic myrmicine ants related to Eutetramorium (Hymenoptera: Formicidae): taxonomy of the genera Eutetramorium Emery, Malagidris nom. n., Myrmisaraka gen. n., Royidris gen. n., and Vitsika gen. n .., Zootaxa 3791 (1), pp. 1-99 : 39-43

Genus Royidris

(Figs 36-80, Maps 134-148)

Royidris Bolton & Fisher gen. n.

Type-species: Monomorium robertsoni Heterick , 2006: 93, by present designation.

Diagnosis of worker

Monomorphic myrmicine ants.

Mandible triangular, masticatory margin with 5 teeth, only slightly longer than basal margin.

Palp formula 5,3.

Stipes of maxilla with a vestigial transverse crest or without a crest.

Clypeus posteriorly moderately broadly inserted between the frontal lobes (width of clypeus between the lobes greater than width of one of the lobes); median portion of clypeus with a fine, weak, longitudinal rugulae on each side, the median longitudinal strip unsculptured.

Clypeus with a stout unpaired seta at the midpoint of the anterior margin.

Clypeus with lateral portions not raised into a shielding wall or sharp ridge in front of the antennal sockets.

Frontal carinae short, restricted to well defined but narrow frontal lobes.

Antennal scrobes absent.

Antenna with 12 segments, with an apical club of 3 or 4 segments.

Torulus with upper lobe visible in full-face view.

Eyes present, relatively large, located at about the midlength of the head capsule, or slightly in front of the midlength. Head capsule without a median longitudinal carina; occipital carina terminates in a distinct ventral prominence in posterodorsal view.

Pronotal humeri rounded in dorsal view.

Pronotum plus anterior mesonotum often swollen and distinctly convex in profile, so that the dorsalmost point of promesonotum is on a considerably higher level than propodeal dorsum (not in admixta group).

Promesonotal suture absent.

Propodeum unarmed, dorsum and declivity separated by a blunt angle; propodeal lobes small and rounded.

Propodeal spiracle at about the midlength of the sclerite and close to the dorsal margin, far in front of the margin of the declivity and separated from apex of metapleural gland bulla by more than the spiracle’s diameter.

Metasternal process absent.

Femora usually incrassate: strongly swollen medially, distinctly tapered proximally and distally.

Tibial spurs: mesotibia 1; metatibia 1; spurs simple.

Abdominal segment 2 (petiole) with an anterior peduncle; spiracle slightly behind the midlength of the peduncle. Subpetiolar process a minute crest.

Abdominal segment 3 (postpetiole) not dorsoventrally flattened in profile, about as high as broad.

Stridulitrum present on pretergite of abdominal segment 4.

Abdominal tergite 4 (first gastral) does not overlap the sternite on the ventral surface of the gaster; gastral shoulders absent to weakly present.

Sting present, usually weakly developed.

Main pilosity of dorsal head and body: simple, usually absent from propodeal dorsum.

Diagnosis of queen (gyne)

Known for admixta, diminuta , notorthotenes , peregrina , and shuckardi , plus two unassociated forms. Alate when virgin, considerably larger than the worker. Characters as worker except for those of the mesosoma; with ocelli developed and a full complement of flight sclerites present. Pronotum in profile is slightly overhung by the convex anterior margin of the mesoscutum; in dorsal view the pronotum is not visible anterior to the mesoscutum, but projects beyond the mesoscutum anterolaterally. Propodeum in profile rounded or with an extremely obtuse angle in diminuta and notorthotenes , in all others with a pair of short, stout, broad-based triangular teeth or prominent angles. Venation: see under male.

Diagnosis of male

Known only for notorthotenes and peregrina . About the same size as the worker or slightly smaller, much smaller than the queen. Mandible reduced, short and narrow, with only 2-3 teeth. Palp formula 5,3. Stipital crest absent. Antenna 13-segmented, filiform. SI 30-35. First funicular segment subglobular, about as broad as long and about 0.50-0.60 x the length of the second funicular segment. Eyes large, at or in front of the midlength of the sides. Ocelli large, on a low turret in notorthotenes ; in full-face view the potsterior ocelli at the posterior margin of the head. Sides of head behind eyes converge strongly to the posterior ocelli. Mesoscutum in profile strongly overhangs the pronotum, the latter not visible in dorsal view. Notauli feeble or with well developed anterior arms that form a V-shape. Mesopleuron with transverse sulcus present. Mesotibia and metatibia each with a single small, simple spur. Propodeum unarmed and rounded; propodeal lobes rounded. Subpetiolar process minute to vestigial. Cerci present.

Forewing venation. Rsf4-5 does not meet Rf3 on anterior margin of wing (= marginal cell open). 2rs-m absent. 1m-cu absent (Rs+M extends without any intersecting cross-vein, from the junction of Rsfl and Mf1 proximally, to the division of Rs+M into Rsf3 and Mf3-4 distally; this division is proximal of the junction with 2r-rs). In one notorthotenes queen a stub of lm-cu is present on the left wing, but not on the right; in another queen a stub occurs on the right wing but not on the left; entirely absent in all other alate material. Af2 not merely a stub distal of cu-a, the latter retracted toward the wing base and arises from M+Cu, proximal of the point where M+Cu divides into Mfl and Cufl-2.

Comments on Royidris

The 15 endemic Madagascan species included in this genus exhibit a habitus that is convergent on some groups of Monomorium . In his study of the Afrotropical members of that genus Bolton (1987: 290) noted two indeterminate Madagascan species which had a high palp formula (5,3), the highest attributed to Monomorium , but did no further analysis of these odd species because the focus of the survey was the extensive Afrotropical fauna. Heterick (2006), in his revision of the Malagasy species of Monomorium , recognised the peculiarity of the high palp formula and utilised it, together with some other characters, to define his M. shuckardi group, all members of which are now transferred to Royidris .

At present, no unambiguous apomorphy can be stated for Royidris , and in fact its habitus is similar to that commonly seen in Monomorium . However, a note of caution must be introduced, because no apomorphies can be cited for Monomorium in its currently accepted form, and it is becoming increasingly obvious that it is polyphyletic. A full survey of its present components, with more detailed morphological and molecular analyses, will be essential if the unwieldy Monomorium is ever to be divided into meaningful monophyletic units that can be awarded generic status. For the present, therefore, members of Royidris can be separated from Monomorium by the presence in Royidris of all the seven following characters in combination: palp formula 5,3; mandible with 5 teeth; antenna 12-segmented, with a club of 3 or 4 segments; propodeal spiracle in profile close to dorsal surface of propodeum; propodeal dorsum usually without setae (one or more pairs of short setae may be present in two species); petiolar spiracle close to midlength of peduncle (not at the node); first gastral tergite does not strongly overlap the sternite on the ventral surface of the gaster.

In Madagascar, and also in Africa, only one Monomorium species, the tramp M. latinode Mayr , has 5 mandibular teeth. However, M. latinode has a palp formula of 3,3, unsculptured mandibles, the eye situated conspicuously far in front of the midlength of the head capsule, the propodeal dorsum transversely costulate and with numerous setae present, the petiolar spiracle at the node, and a first gastral tergite that strongly overlaps the sternite ventrally.

Species groups of Royidris

Three groups of species can be isolated on worker morphological grounds within the genus. The groups are currently defined for convenience and ease of identification, and do not necessarily reflect accurate phylogeny.

1 The admixta group ( admixta , depilosa ). Antennal club of 3 segments (Figs 36, 47). Promesonotum not swollen or domed: in profile the dorsum flat or nearly so, evenly sloping posteriorly to the metanotal groove. Propodeal dorsum behind the metanotal groove approximately continues the line of the promesonotal outline; the propodeal dorsum is not considerably depressed below the level of the promesonotum (Figs 36, 45). Scapes and metafemora in the group are among the shortest in the genus (SI 90-95, MfL/HW 0.90-0.95), and the postpetiole is the broadest (maximum dorsal width 0.42-0.48 x HW). In all other species combined, these measurements show ranges of SI 90-158 (SI <100 only in some workers of gravipuncta and clarinodis ), MfL/HW 0.95-1.50 (again, MfL/HW <1.00 only in some workers of gravipuncta and clarinodis ), maximum dorsal width of postpetiole 0.27-0.39 x HW (outside the admixta group 0.39 x HW is achieved only in longiseta ).

The two species included here form a closely related pair, separated by differences in sculpture and pilosity. Both were inexplicably included as conspecific with clarinodis by Heterick (2006), whose description obviously included elements of several species that are recognised as separate here.

2 The robertsoni group ( anxietas , clarinodis , pallida , pulchra , robertsoni ). Antennal club of 3 segments (Figs 39, 42, 63, 69, 72). Promesonotum swollen or domed: in profile the dorsum convex and appearing swollen, the posterior outline of the mesonotum descends steeply, and usually abruptly, to the metanotal groove (or the junction with the propodeum in those species where the groove is suppressed). Propodeal dorsum behind the metanotal groove horizontal or sloping, decidedly not continuing the line of the promesonotal outline; the propodeal dorsum is strikingly depressed below the level of the promesonotal dorsum (Figs 39, 42, 63, 69, 72). The scape is generally shorter in this group (SI 90-110) than in the notorthotenes group (SI 95-158). In the robertsoni group the only workers with SI <95 are some individuals of clarinodis , while in the notorthotenes group only some individuals of gravipuncta have SI <100.

Together with the two species now placed in the admixta group, four of the five names included in this group were regarded as conspecific with clarinodis by Heterick (2006); only robertsoni was treated by him as a species separate from clarinodis . The group falls into two uneven complexes of species depending on whether the metanotal groove is conspicuously retained and the eyes are obviously in front of the midlength of the side of the head capsule ( clarinodis ), or the metanotal groove is suppressed and the eyes are at, or very close to, the midlength ( anxietas , pallida , pulchra , robertsoni ).

3 The notorthotenes group ( diminuta , etiolata , gravipuncta , longiseta , notorthotenes , peregrina , shuckardi , singularis ). Antennal club of 4 segments (Figs 51, 57, 62, 66). Promesonotum domed: in profile the dorsum convex and appearing swollen, the posterior outline of the mesonotum descends steeply, and usually abruptly, to the metanotal groove. Propodeal dorsum behind the metanotal groove horizontal or nearly so, decidedly not continuing the line of the promesonotal outline; the propodeal dorsum is strikingly depressed below the level of the promesonotal dorsum (Figs 48, 51, 54, 57, 60, 66, 78).

Both of the species that Heterick (2006) recognised, notorthotenes and shuckardi , are now considered to be compound, with diminuta and etiolata being split from his concept of notorthotenes , and longiseta and gravipuncta split from his concept of shuckardi . The two final species, singularis and peregrina , had not been discovered at the time of his study. Three complexes of species can be identified within the group. The first complex includes longiseta , gravipuncta and peregrina , and is characterised by denser, heavier cephalic sculpture, darker colour, relatively shorter scapes (SI 95-117), head that averages relatively broader (CI 82-89), and shorter metafemora

(MfL/HW 0.95-1.13). The second complex, which consists of diminuta , etiolata and notorthotenes , has cephalic sculpture that is weak to vestigial, uniform yellow in colour, relatively longer scapes (SI 115-158), head that averages relatively narrower (CI 75-84), and longer metafemora (MfL/HW 1.25-1.50). The final complex, which contains only singularis , exhibits a mixture of the features of the other two complexes. Its sculpture is largely suppressed (the head and dorsal pronotum are glassy smooth), its scapes are long (SI 121), and its body is darkly coloured; it has MfL/HW 1.13, at the top end of the range of the gravipuncta complex but well below that of notorthotenes and its relatives. R. shuckardi cannot be placed in any complex as it is known only from a single queen, but its 4-segmented antennal club indicates its placement within this species group.

Synopsis of Royidris species

admixta group

admixta Bolton & Fisher sp. n.

depilosa Bolton & Fisher sp. n.

robertsoni group

anxietas Bolton & Fisher sp. n.

clarinodis (Heterick, 2006) comb. n.

pallida Bolton & Fisher sp. n.

pulchra Bolton & Fisher sp. n.

robertsoni (Heterick, 2006) comb. n.

notorthotenes group

diminuta Bolton & Fisher sp. n.

etiolata Bolton & Fisher sp. n.

gravipuncta Bolton & Fisher sp. n.

longiseta Bolton & Fisher sp. n.

notorthotenes (Heterick, 2006) comb. n.

peregrina Bolton & Fisher sp. n.

shuckardi (Forel, 1895) comb. n.

singularis Bolton & Fisher sp. n.

Key to Royidris species (workers)

( R. shuckardi is excluded as only its queen is known.)

1 Antennal club of 4 segments (Figs 51, 57, 60, 62, 66): in general, funiculus segments 8 and 9 appear very similar in length and volume. Funiculus segment 8 appears distinctly larger and more voluminous than segment 7. Segment 8 is disproportionately enlarged, out of proportion with the gradual increase in size of funiculus segments 4-7..............................2

- Antennal club of 3 segments (Figs 36, 42, 47, 63, 69, 72): in general, funiculus segment 8 appears distinctly smaller and less voluminous than segment 9. Funiculus segment 8 is only slightly larger than segment 7. Size of segment 8 is in proportion with the gradual increase in size of funiculus segments 4-7 ........................................................8

2 With head in full-face view the dorsum between and behind the eyes with conspicuous sculpture present (Figs 55, 58, 67). Mid-dorsal strip of head, behind the frontal carinae, distinctly more strongly sculptured than the clypeus. Scape averaging shorter, SI 95-117.....................................................................................3

- With head in full-face view the dorsum between and behind the eyes smooth or very nearly so, at most the surface with vestigial punctulate sculpture or superficial microreticulate patterning (Figs 50, 52, 61, 79). Mid-dorsal strip of head, behind the frontal carinae, as smooth as, or only fractionally more sculptured than, the clypeus. Scape averaging longer, SI 115-158...5

3 With mesosoma in profile, the longest setae on the promesonotal dorsum are distinctly longer than the maximum vertical diameter of the eye at its midlength (Fig. 57). Propodeal dorsum with 2 or more pairs of short, standing setae longiseta

- With mesosoma in profile, the longest setae on the promesonotal dorsum are distinctly shorter than the maximum vertical diameter of the eye at its midlength (Figs 54, 78). Propodeal dorsum without standing setae, at most a few minute, decumbent pubescence hairs present................................................................................ 4

4 Reticulate-punctate sculpture of cephalic dorsum strong and usually of uniform density everywhere (Fig. 55). Pronotal dorsum densely reticulate-punctate, often also with weak transverse striolae; pronotal dorsum usually as strongly and densely sculptured as the propodeal dorsum (Fig. 56). First gastral tergite superficially microreticulate. Scape and metatibia relatively shorter, SI 95-107 (mean SI 101), MfL/HW 0.95-1.06 ............................................... gravipuncta

- Reticulate-punctate sculpture of cephalic dorsum fine and more diffuse, the sculpture may be partially or mostly effaced (Fig. 67). Pronotal dorsum with reticulate-punctate sculpture very weak to effaced, never with transverse striolae; pronotal dorsum not as strongly or densely sculptured as the propodeal dorsum (Fig. 68). First gastral tergite glassy smooth. Scape and metatibia relatively longer, SI 108-118 (mean SI 113), MfL/HW 1.08-1.13...................................... peregrina

5 Brown species with black gaster. Dorsum of head glassy smooth, with widely scattered minute punctures. Pronotal dorsum glassy smooth, without punctulate or microreticulate sculpture (Figs 78-80). Eyes smaller, EL/HW 0.28. Metafemur relatively shorter, MfL/HW 1.13........................................................................... singularis

- Uniformly yellow species. Dorsum of head with superficial microreticulate or reticulate-punctulate sculpture, at least in part. Dorsum of pronotum partially to mostly microreticulate to punctulate (Figs 48-53, 60-62). Eyes larger, EL/HW 0.29-0.32. Metafemur relatively longer, MfL/HW 1.25-1.50 ............................................................6

6 Scape relatively very long, SI 148-158. Metafemur longer and somewhat less strongly incrassate, MfL/HW 1.46-1.50, MfL/ MfH 4.00-4.38 .................................................................................. etiolata

- Scape relatively shorter, SI 115-132. Metafemur shorter and somewhat more strongly incrassate, MfL/HW 1.25-1.39, MfL/ MfH 3.36-4.15.......................................................................................7

7 Larger species, HL 0.80-0.98, HW 0.65-0.81, SL 0.86-1.00, EL 0.20-0.24............................. notorthotenes

- Smaller species, HL 0.66-0.73, HW 0.50-0.58, SL 0.66-0.73, EL 0.16-0.18............................... diminuta

8 Promesonotum in profile slopes gradually and shallowly posteriorly to the metanotal groove; propodeal dorsum behind the metanotal groove approximately continues the line of the promesonotum and is not strongly depressed below the level of the promesonotal dorsum (Figs 36, 45). Postpetiole relatively broad, its maximum width in dorsal view 0.42-0.48 x HW 9

- Promesonotum in profile convex, swollen or dome-like, descending steeply posteriorly to the metanotal groove (or the junction of mesonotum and propodeum in species where the metanotal groove is suppressed); propodeal dorsum is strongly depressed below the level of the promesonotal dorsum and does not continue its line (Figs 39, 42, 63, 69, 72). Postpetiole relatively narrow, its maximum width in dorsal view 0.33-0.38 x HW..............................................10

9 Dorsum of pronotum without a seta at the humeral angle (Fig. 45). Posterior face of petiole node without setae. First gastral tergite without setae except for a few at the extreme apical margin. With head in full-face view the dorsum smooth and polished, with scattered minute punctulae on a glossy surface (Fig. 46)........................................ depilosa

- Dorsum of pronotum with a standing seta at the humeral angle (Fig. 36). Posterior face of petiole node with a pair of setae. First gastral tergite with scattered setae, located anterior to those at the extreme apical margin. With head in full-face view the dorsum densely microreticulate to reticulate-punctulate everywhere (Fig. 37)................................ admixta

10 Dorsum of head between and behind the eyes sculptured, the surface either finely reticulate-punctate or densely shagreenate-striolate (Figs 40, 73) ................................................................................. 11

- Dorsum of head between and behind the eyes unsculptured, the surface smooth except for minute and widely scattered pits (Figs 43, 64, 70)..................................................................................... 12

11 In profile the propodeal dorsum slopes downward posteriorly and is confluent with the declivity through a broad, shallow curve (Fig. 72); without a pair of short, erect setae on the curve. Dorsum of head to the level of the posterior margins of the eyes finely, densely shagreenate and with weak, superficial striolae, the whole surface with a silky appearance. Posterior to the level of the eyes the shagreenate component weaker and the striolae tend to be transverse. Pronotal dorsum shagreenate-striolate. Full adult colour of head and mesosoma yellow. Metafemur shorter and more strongly incrassate, MfL/HW 1.07-1.09, MfL/MfH 3.86-4.50 ........................................................................... robertsoni

- In profile the propodeal dorsum horizontal, not sloped downward posteriorly; dorsum meets the declivity through a blunt rightangle (Fig. 39); with a pair of short, erect setae on the dorsum just before the angle. Dorsum of head everywhere superficially punctulate to reticulate-punctulate, without a silky appearance. Pronotal dorsum mostly smooth, with only feeble superficial punctulae present. Full adult colour of head and mesosoma brown to dark brown. Metafemur longer and less strongly incrassate, MfL/HW 1.17-1.22, MfL/MfH 5.50-5.64........................................................ anxietas

12 With mesosoma in profile the metanotal groove distinctly impressed; a V-shaped or narrowly U-shaped conspicuous impression present between base of mesonotum and propodeum (Fig. 42). Mandible smooth, with scattered small pits. With head in full-face view the eyes distinctly in front of the midlength of the side of the head capsule (Fig. 43). Eye smaller, EL/HW 0.22-0.26. Metafemur shorter and more incrassate, MfL/HW 0.93-1.04, MfL/MfH 3.67-4.00.................. clarinodis

- With mesosoma in profile the metanotal groove not impressed; without a V-shaped or narrowly U-shaped impression between base of mesonotum and propodeum (Figs 63, 69). Mandible with fine longitudinal costulae. With head in full-face view the eyes very close to the midlength of the side of the head capsule (Figs 64, 70). Eye larger, EL/HW 0.28-0.32. Metafemur longer and less incrassate, MfL/HW 1.12-1.32, MfL/MfH 5.60-6.00 ................................................. 13

13 Head and mesosoma uniformly yellow, gaster paler, very pale yellow (Fig. 63). Lower half of side of pronotum without punctate sculpture such as occurs on the mesopleuron. Smaller species with relatively shorter scape, smaller eye (Fig. 64), and shorter metafemur, HW 0.50, SL 0.50, SI 100, EL/HW 0.28, MfL/HW 1.12.................................. pallida

- Head and mesosoma brown, gaster darker, black (Fig. 69). Lower half of side of pronotum with punctate sculpture similar to that present on mesopleuron. Larger species with relatively longer scape, larger eye (Fig. 70), and longer metafemur, HW 0.59, SL 0.66, SI 112, EL/HW 0.32, MfL/HW 1.32......................................................... pulchra