Igaponera curiosa ( MacKay & MacKay, 2010 ) (MacKay & MacKay, 2010)

Troya, Adrian, Marcineiro, Frederico, Lattke, John E. & Longino, John, 2022, Igaponera curiosa, a new ponerine genus (Hymenoptera: Formicidae) from the Amazon, European Journal of Taxonomy 823, pp. 82-101 : 90-97

Igaponera curiosa ( MacKay & MacKay, 2010)

Fig. 3A–D

Pachycondyla curiosa MacKay & MacKay 2010: 295 , figs 423–424. Holotype queen: Brazil, Amazonas , Rio Tarumã-Mirím, Igapó; 6 Jan. 1976; J. Adis leg.; Jt-1. [Los Angeles County Museum of Natural History, unique specimen identifier LACM-ENT226103 ] (examined).

Neoponera curiosa Mackay & Mackay 2010 ; Esteves & Fisher 2021: 103 (combination in Neoponera ).

Diagnosis

As for genus.

Measurements

HL 1.52; HW 1.38; ML 0.74; EL 0.39; EW 0.29; SL 1.07; PrW 1.13; WL 2.43; PH 0.98; PW 0.84; PL 0.79; MetL 1.20. Indices: CI 91; OI 28; MI 49; SI 78; PI 106.

Description

Queen (holotype)

HEAD ( Fig. 3B–C ). Subquadrate in dorsal view, posterior margin straight; lateral margin mostly weakly convex, posterolaterally curving mesad. Eye surface convex, shape in perpendicular view elongate ovoid, three-fourths longer than wide. Anterior clypeal margin in dorsal view shaped as broadly obtuse angle with blunt apex. Cephalic dorsum mostly with diverging costae, some longitudinal costae present between ocelli, vertex longitudinally costate. Three relatively small, one-sixth of eye length, similarsized ocelli placed on posterior third of head, distance between ocelli approximately 3× diameter of each ocellus. Lateral margin of frontal lobe convex, dorsal surface convex with lateral margin higher than mesial margin, dorsum mostly smooth with scattered punctulae; lobe covers most of scape basal condyle in cephalic dorsal view, neck exposed. Genae longitudinally rugulose. Vertexal carina arched. Clypeus with lateral surface projecting dorsoanteriorly as inclined shelf, laterally finely rugulose, close to antennal sclerite smooth with punctulae, median clypeus raised with blunt longitudinal shining convexity, anterior margin with coarse punctae. Supraclypeal area extends posteriorly between frontal carinae, slightly surpassing level of anterior eye margin. Scape mostly smooth with abundant piligerous punctulae, gradually widening apicad, surface with abundant appressed pubescense and scattered decumbent and subdecumbent hairs, none longer than scape width. Scape barely reaches posterior cephalic margin when pulled back. Antennomere II elongate campaniform; antennomeres II–IV slightly broader than long, antennomeres V-XII noticeably broader than long, apical antennomere longest, with blunt tip. Each funicular piece with decumbent hairs, especially towards apical margin. Mandible with convex dorsal surface, mostly smooth with scattered elongate punctae, transverse basal ridge present, laterobasal area rugulose and with rounded depression; masticatory margin with 4 short, similar-sized triangular teeth on apex and 5 stout denticles basad to teeth. Cephalic ventral surface mostly flattened with slightly elevated anteromedian triangular-shaped region on hypostomal region; mostly transversely striate, discal area tending to smooth. Postgenal ridge weakly impressed, appearing as series of small, shallow depressions. Labrum broader than long, dorsum mostly smooth and shining, with basal transverse convexity, anteromedially with angular cleft. Prementum smooth and shining, ventral surface convex; medially with tenuous transverse premental groove. Palp formula: 4,4. Hypostoma widest mesad, forming smooth and shining narrow strip, hypostomal tooth with lateral twist, vertical to cephalic ventral surface and with blunt point. Stipes apically bidentate; external margin broadly convex. Cephalic dorsum with abundant erect to suberect anteriorly arching hairs, hairs on cephalic venter straighter and longer. Anterior clypeal margin with long, golden straight setae, and sparse short setae and hairs.

MESOSOMA ( Fig. 3A–D ). Dorsal margin of pronotum, mesonotum and propodeum weakly convex, almost straight. Propodeum convex with declivitous margin longer than dorsal margin. Most of pronotal lateral margin longitudinally irregularly costate, ventrolateral margin bound by sulcus with several transverse ridges; humeral carina completely absent; anepisternum with costae parallel to anapleural sulcus, sulcus broad and deep; katepisternum with oblique to longitudinal costae; anteroventral mesopleural carina distinct. Mesometapleural suture well-impressed, metapleuron and lateral propodeal face with oblique irregular costae; metapleural-propodeal suture weakly impressed. Pronotal dorsum with concentric anteriorly convex costae. Most of mesonotum longitudinally costate, costae slightly arched along lateral margins of scutum. Transcutal suture fine but distinct, scutoscutellar sulcus broad and shallow, not breaking costae. Metanotum transverse, longitudinally costulate. Wing stumps evident. Propleuron transversely costate, anterior one-third narrow, anterior surface in lateral view bent at approximately 120° angle to posterior surface. Prosternum shaped as ventroposteriorly pointing triangular lobe in ventral view. Ventral surface of mesopleuron transversely costate. Mesocoxa anteriorly bound by mesosternal process shaped as elongate right triangle with blunt apex; metasternal process shaped as bluntly-pointed, flattened lobe; metacoxal cavity closed. Propodeal spiracle slightly protruding, opening directed posterolaterally; spiracle situated at propodeal midlength, close to metapleuron. Propodeal dorsal and declivitous faces transversely costate, separation between lateral and declivitous surfaces bluntly angular; dorsal face shorter than declivitous face. Metapleural ventral margin bordered by broad, shallow sulcus.

LEGS ( Fig. 3A, B ). Protibial apex with single preapical seta and robust, apically pectinate calcar with basal velum; posterior margin of velum slightly rounded and shorter than anterior pointed margin; strigil comb opposite calcar with row of tooth-like setae, posterior basitarsal face, distad of comb, densely clothed with decumbent appressed golden hairs. Procoxa and profemur mostly smooth and shining, protibia densely punctulate. Meso- and metatarsi with abundant hairs, some relatively thick, but none shaped as short, stout, spine-like setae. Length of arolium not more than one fourth of claw length.

PETIOLE ( Fig. 3A–B, D ). Sessile; node in lateral view subquadrate, higher posterad than anterad; anterior margin vertical, weakly concave; dorsal margin weakly convex, posterior margin vertical. Node anterolaterally with short, robust projection, spiracle placed just posterad to projection; lateral nodal face longitudinally costate on ventral half, costae oblique and thicker on dorsal half. Tergosternal suture well-marked. Petiolar sternite projects ventrally as broad longitudinal ridge with transverse costae; ventral margin of sternite in lateral view broadly convex with brief carinate concavity just posterad of anterior process; petiolar process in lateral view with convex anterior margin ending in brief posteriorly curved point; process in ventral view forms anteriorly-pointing angle. Node in dorsal view shaped as robust isosceles trapezoid, slightly wider posterad, anterior petiolar margin concave with incomplete transverse carina, anterior margin of node broadly convex, lateral margin broadly convex, posterior margin straight. Dorsal face mostly transversely costate with posterior costae arched. Anterior and posterior faces transversely costate. Petiole without posterior shelf.

GASTER ( Fig. 3B, D ). Helcium low on anterior face of abdominal segment III, pretergite overlapping presternite. Anterior margin of abdominal tergite III in lateral view straight, vertical, forming blunt, obtuse angle with dorsal margin; most of sternoventral margin broadly convex. Dorsal gastral margin in lateral view mostly convex, dorsal margin of abdominal segment IV 2× as long as ventral margin. Gaster mostly smooth and shining with scattered shallow, piligerous punctae; dorsum of abdominal tergite III with more abundant and slightly deeper punctae than on tergite IV; anterior face of tergite III flattened, without piligerous punctae. Spiracles visible on abdominal segments III, IV, and V. Epipygium mostly smooth and shining, broadly convex in transverse section, not laterally compressed, posterolaterally with fine striae converging posteriorly towards stinger with smooth patch in middle; short posteromedian longitudinal carina present, less than one-eighth length of epipygium, ventrolaterally with abundant punctae; robust sting, surrounded by abundant short hairs.

PILOSITY. Mesosoma, legs, and node with abundant short decumbent pilosity, mesosoma in lateral view with abundant erect and suberect hairs; gaster with sparse appressed pilosity mostly on third tergite, rest with abundant erect to suberect hairs. Anterior and posterior faces of meso- and metacoxa densely pubescent.

COLOR. Head, mesosoma, and petiole black; mandible ferruginous, masticatory margin dark brown; palps yellow; antenna and legs dark ferruginous brown; gaster ferruginous brown. Masticatory margin darker than rest of dorsal mandibular surface.

Discussion

Phylogeny

In the genomics era, morphology-based phylogenies are increasingly uncommon, particularly when dealing with hundreds or even thousands of taxa (e.g., Pyron et al. 2013; Wiemers et al. 2020). Testing relationships based on scored character statements is thus generally the norm when organisms with low-quality or degraded DNA are at play. Although the morphological data set we used was small, as compared, for example, to that of Keller (2011) where the author used 139 character statements, it is enough to inform us about the approximate placement of a rare specimen within the Ponerinae .

Although the statistical resampling returned unresolved, but relatively well supported topologies under parsimony, the more resolved, though not strongly supported topology, under the likelihood approach, partially sustains our hypothesis in regards to the independence of Igaponera from its closest lineages, Neoponera and Pachycondyla . With the following arguments, we further support this phylogenetic inference:

The strongly costate sculpture of Igaponera is definitely an unusual trait for a Pachycondyla group member, or even for a ponerine! However, based on its overall external body features, we found this lineage to be similar in appearance to only three genus lineages within the Pachycondyla group: Mayaponera , Neoponera , and Pachycondyla . Among them, the latter two display more similarities with the new genus, and the following characters can be considered useful for distinguishing their close relationship.

The lobate projections on the fourth protarsomere (char. 27, state 0) is a trait shared among Igaponera , Neoponera , Pachycondyla , and Dinoponera . The trait is conical (state 1) in Mayaponera , whereas in Simopelta and Thaumatomyrmex , here considered distantly related to Igaponera , it is cylindrical (state 2). According to Keller (2011), these transformations are additive, and based on the phylogenies of Schmidt & Shattuck (2014) and Branstetter & Longino (2022), the cylindrical condition is ancestral to a more derived lobate structure which is present in what could be the more derived lineages of the Pachycondyla genus group, including Igaponera .

The degree of fusion of the laterotergite of the petiole and the petiolar node (char. 30) is a character that varies in ponerines. As here considered, the plates are partially fused (state 0), revealed by a suture along the margins. This character state is shared among Igaponera and its closely related lineages, plus Mayaponera . The opposite condition, where the plates are fully fused (state 1), is present in Simopelta and Thaumatomyrmex . Outside of the genus group, this latter trait is also present in Rasopone Schmidt & Shattuck, 2014 , a morphologically similar lineage whose phylogenetic affinities within the Ponerinae are still unclear.

Despite showing variations across many ponerine genera, the outline of the velum on the strigil’s calcar [also called “basoventral lamella” in Esteves & Fisher (2021), or just “basal lamella” in Keller (2011)], can be classified in easily discernible patterns among the Pachycondyla group lineages where this trait is well-developed. In Neoponera , the velum is mostly round at its base, except for N. concava , N. schultzi , and N. venusta , where it is subtriangular; in Pachycondyla , it is horizontally straight; and in Igaponera curiosa , it is slightly rounded, but similar to most Neoponera . These variations were not scored as character statements in our matrix, but we think they are phylogenetically informative and should be considered in future studies.

Finally, we concur with Esteves & Fisher (2021) in the sense that I. curiosa “conforms with the characters shared by Neoponera and Pachycondyla ” (p. 103). In the next line, though, they remark: “In addition, the species possesses a stridulitrum on the pretergite of abdominal segment IV” (p. 103), citing Mackay & Mackay (2010). We thoroughly examined this region and can confirm that it is absent, as in all Pachycondyla species. In Neoponera , on the other hand, this structure is always present, either faintly or strongly impressed.

Identifying Igaponera

The queen of this species will run to couplet 6 in the key to Neotropical ponerine genera by Schmidt & Shattuck (2014), where it fits into Pachycondyla more than Neoponera because it lacks a stridulitrum, the arolia are not prominent, and there is no malar carina. Nonetheless, a number of Neoponera species also lack a malar carina, and some species show non-prominent arolia. In the key to ponerine genera for Colombia by Fernández & Guerrero (2019), Igaponera runs to couplet 13 but does not fit either of the two alternatives as it has the node shape described for Pachycondyla and not for Neoponera . In addition, Igaponera lacks the stout, spine-like hypopygial setae typical of Pachycondyla , which are also present in most species of the Neoponera crenata species-group, as noted also in Esteves & Fisher (2021). In the latest key to Neotropical ponerine genera by Esteves & Fisher (2021), Igaponera runs to couplet 18 leading to Pachycondyla and Mayaponera , but not exactly fitting either lead because it has a slit-shaped propodeal spiracle but lacks hypopygial aristate and spine-like setae. Its costate sculpture will immediately differentiate it from those genera, however.

As mentioned before, within the Pachycondyla group, Igaponera bears closest overall resemblance to Mayaponera , Neoponera , and Pachycondyla , but outside that genus group it is also morphologically similar to Pseudoponera and Rasopone . However, the following frequently used diagnostic traits of these genera are not found in Igaponera :

Mayaponera : Species in this genus have relatively smaller eyes placed anteriorly on the head, elongate mandibles with about 12 teeth, a rounded to oval propodeal spiracle, a scale-shaped petiole and no prora. Mayaponera constricta has relatively larger eyes than the other species in the genus, but they are flattened and do not attain the relative size present in Igaponera .

Neoponera : all the species in this genus have a stridulitrum on the abdominal pretergite IV, usually prominent arolia on the pretarsal claws, and many species bear distinct malar carinae. This genus shows great morphological variation and indeed some of the diagnostic characters for Igaponera can also be found in Neoponera .

Pachycondyla : this genus has smaller eyes placed anteriorly on the head, elongate mandibles with 7-11 teeth, frequently an anterolateral carina on the pronotum, and no arolia on the pretarsal claws. Pachycondyla species generally have a cuboid petiolar node approximating the shape in Igaponera , but the node in this genus, in lateral view, has a straight anterior petiolar margin and a weakly convex to almost flat dorsal margin that is higher than the posterior margin, usually with the posterior face curving anteriorly near the apex; the length of the propodeal declivitous margin, in lateral view, is relatively longer than in Igaponera , and forms a more open obtuse angle with the dorsal margin.

Pseudoponera : these are much smaller ants with small eyes placed on the anterior part of the head, the mandible has 5–7 teeth, the propodeal spiracle is rounded, the petiolar node is scale-shaped, the pretarsal claws lack arolia, the dorsum of the propodeum narrows anteriorly, and the clypeus often bears a transverse carina.

Rasopone : ants in this genus have elongate mandibles with an average of 12 teeth, relatively small ocelli, round or ovoid propodeal spiracles, the petiolar sternite with a posterior transverse groove, and no prora; the petiolar node is usually scale-shaped, but if thickened, then the anterior and posterior faces are flattened and parallel to each other ( Longino & Branstetter 2020).

Comparative morphology of diagnostic characters

Perhaps the most outstanding diagnostic morphological feature of this ant is the costate sculpturing that covers most of its body, particularly on the cephalic dorsum, most of the mesosoma, and the petiole. Such sculpture is more typical in Neotropical Gnamptogenys Roger, 1863 , but not in Ponerinae . There are no other Neotropical ponerines that bear such sculpturing extensively over their bodies and the only species that come close are two Neoponera species: N. lineaticeps and N. magnifica . The former species has a patch of costulae on the median frons only, and the latter has costulae on the cephalic and pronotal dorsum, and sometimes variably developed on the mesonotum. The costulae of these species are relatively narrower and shallower than in I. curiosa . Ponerines from other biogeographic regions with similar costulae include the genus Diacamma Mayr, 1862 , Paltothyreus tarsatus , an African species with costulae on the promesonotum only, and the Indomalayan Odontoponera Mayr, 1862 which bear costulae on the head and mesosomal dorsum.

The antennal scape in Igaponera fails to reach the posterior cephalic margin (by less than one apical width) when pulled back. In Neoponera , the scape usually surpasses the posterior cephalic margin by at least one apical width. Only two species in the N. laevigata species group and N. fisheri have a scape that fails to reach the posterior cephalic margin.

The mandibles in Igaponera are relatively short and robust, with short, robust teeth and denticles, and the apical tooth is not noticeably longer than the preceding teeth. This gives the mandibular apex a blunt shape, unlike in Neoponera and many other ponerines in which an acute apical angle gives the mandible an elongate triangular shape. Exceptions are found in N. magnifica , N. fisheri , and N. luteola , all with a mandible not as elongate as in other Neoponera , but they still have an acute apical angle, distinctly different from the state in Igaponera . Pseudoponera mandibles appear not as elongate as in the other genera, but they do not exhibit the condition in Igaponera . This morphology suggests Igaponera may use their mandibles for chewing upon hard items, perhaps heavily armored prey.

The base of the hypostomal tooth is recessed below the surrounding surface of the hypostomal bridge in I. curiosa , and the tip of the tooth is directed vertically to the surrounding cephalic surface. In the studied specimens of Neoponera , Pachycondyla , Mayaponera , Rasopone , and Pseudoponera , this base is approximately on the same plane as the surrounding ventral cephalic surface and the tooth itself is not raised vertically but projects anteriorly or anterolaterally. In most Neoponera , the hypostomal margin forms an arch when the head is seen anteriorly, with the median region higher than the lateral extremities. The lateral hypostomal tooth projects anterad as a continuation of this arch.

The metapleural gland opening in Igaponera is enclosed dorsally by a flange that conceals it in dorsal view. Such a structure is absent in the studied specimens of Neoponera , Pachycondyla , Rasopone , Mayaponera and Pseudoponera , and the gland opening in these taxa can be partially seen in dorsal view. The lack of a dorsal lobe or carina that hides the metapleural gland opening is considered a trait of Ponerinae by Bolton (2003). Nevertheless, a similar variation of this flange is found in Simopelta pergandei and S. oculata (ANTWEB1008588, SEM images), but the structure of the gland opening is completely different compared to all the aforementioned genera, suggesting independent development from that of Igaponera .

Mackay & Mackay (2010) described the existence of a stridulitrum for this species but we examined the fourth abdominal pretergite at 60× and were not able to detect a structure we could identify as such. We did find a small irregularly-shaped patch that changes shape depending upon the angle of incident light, but its structure and size do not suggest a stridulitrum as it lacks the typical iridescence. In a few Neoponera , for example N. commutata and N. laevigata , the stridulitrum may not form a typical triangular-shaped structure, but it is still recognizable as a stridulitrum. It is shaped as a relatively much narrower, sub-triangular, dashed patch with iridescence. The presence of a stridulitrum is a diagnostic character for Neoponera ( Schmidt & Shattuck 2014) , prompting Esteves & Fisher (2021) to use its supposed presence in Igaponera as support for transfering the species from Pachycondyla to Neoponera .

Neoponera , Pachycondyla , Mayaponera , Pseudoponera , and Rasopone have a variable number of setae of differing development on the apex of the meso- and metatibiae, but the setae are totally absent in Igaponera . Also, the apical margin of each meso- and metatarsomere in the aforementioned genera usually bears stout setae. These setae have a polished appearance and are typically darker than the surrounding pilosity, suggesting greater sclerotization and stiffness, regardless of their relative thickness. The apices of the meso- and metatarsal segments in Igaponera have elongate, lighter colored setae that are not polished but bear a sheen. Some are slightly arched, and overall their appearance suggests diminished stiffness. Similar setae can be found in species such as Pseudoponera stigma and Neoponera crenata . A dorsal transverse strip of rugosity adjacent to the third abdominal pretergite, just posterad to the helcium, is present in Igaponera and absent in Pachycondyla , Mayaponera , Pseudoponera stigma , and most Neoponera , though Neoponera foetida , N. latinoda , and N. inversa have rugulae in this region. Mayaponera arhuaca and R. lunaris exhibit a narrow band of very fine rugosity in this region.

Notes on the habitat of I. curiosa

This ant was collected by Dr. Joachim Adis (1981) during a study of the arthropod fauna inhabiting the Rio Tarumã Mirim Igapó, a seasonally flooded, black water forest 20 km upstream from Manaus, close to where the Rio Tarumã Mirim empties into the Rio Negro. The type locality coordinates are 03°02ʹ S, 60°17ʹ W (-3.03, -60.28) according to Adis (1981: fig. 1), but these coordinates indicate a point 25 km west of the Eduardo Gomes International Airport of Manaus, not coinciding with the location of the collection site depicted in figures 1 & 2 from Adis (1981). Using the graphic location of both figures, the coordinates should be approximately -3.02, -60.17, a site 14 km west of the airport, barely 20 m above sea level.

Adis sampled using pitfall traps, ground photo-eclectors and arboreal photo-eclectors. The arboreal traps were designed to catch insects moving on tree trunks. His specimens were killed and then preserved for an indeterminate amount of time in an aqueous solution of picric acid. Since the seasonal flooding permits only a scant layer of leaf litter to accumulate at the end of the dry season, it is assumed this species is more likely an arboreal rather than a leaf-litter or subterranean ant, despite having very small arolia.

Due to its proximity to Manaus, the area where this specimen was found is frequently used for research purposes by academic programs, such as those of INPA. The voucher specimens collected by Adis are deposited in the INPA collection. One of us searched for additional specimens there, but none could be found, suggesting it is a relatively rare species or has a biology that keeps it from being frequently collected by the usual field techniques. The large eyes could imply activity in low-light conditions, such as during the night, but also this is a functional trait linked to flight, for example, during mating and nest search ( Julian & Gronenberg 2002; Peeters et al. 2013).

Figures

Fig. 3. Igaponera curiosa (Mackay & Mackay, 2010), holotype queen. A. Body in dorsal view. B. Body in lateral view. C. Head in frontal view. D. Petiole in lateral view. Additional images available on AntWeb (www.antweb.org). Scale bars: A–B = 1 mm; C–D = 0.5 mm.