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This species belongs to the Middle American clade of Stenamma (see Branstetter 2012). All conent on this page modified from Branstetter (2013) unless noted otherwise.
Mexico to Nicaragua. No records from Belize.
This species is one of the largest and most conspicuous species of Stenamma, which is probably why it was the first Middle American species to be described. As defined here, S. manni occurs from 1200–3700 m elevation, but it seems to be most common between 2000–2500 m. It occurs in wet montane forests like cloud forest, and drier, more seasonal habitats, such as oak woodland. Specimens have been collected in leaf litter samples, at bait cards, in Malaise traps, and by general searching. I have found nests in logs, in the leaf litter, under rocks, and in the ground. In Central America, S. manni is commonly found at the edge of cloud forest in logs and in the ground under logs. All Stenamma manni nests tend to be very large, with hundreds to perhaps over a thousand workers (a complete colony census has not been carried out). Nests usually have brood, alates, and a single egg-laying queen. Stenamma manni is one of the most common Stenamma species to be found at bait cards, suggesting that they are active epigeic foragers. All foragers I have observed have been solitary.
Stenamma manni should be separable from most similar species by the combination of presence of a lateral hypostomal lobe; presence of tuberculate to short propodeal spines; and large body size. However, it should be evident from the worker description in Branstetter (2013) that S. manni, as currently circumscribed, is highly variable, and thus difficult to characterize in a very satisfactory way. Indeed, the manni complex, with all of its different variants, is a taxonomic nightmare. Nearly every population has unique, often distinctive features, and there is no evidence of sympatry among forms. It is also common to have populations that are intermediate in phenotype between variants. Because of this diversity, Branstetter (2013) has united most forms, even if very distinct, into one polytypic species. Many variants are described below, providing distinguishing characters for each and approximate geographic ranges. This should help in identification of S. manni as Branstetter (2013) has defined it, and will provide guidelines for future work on the complex.
One S. manni-like variant that was recognized as a distinct species is S. megamanni. This species occurs from Chiapas, Mexico to Nicaragua and is sympatric with S. manni at many sites. However, it is a variable species and difficult to recognize from S. manni at a large geographic scale. Within the range where both species occur, two forms are often found in sympatry. What Branstetter (2013) calls S. manni always has lighter body color (usually dark red-brown), a smaller eye (usually 5–6 ommatidia at greatest diameter), and a larger, more bulging postpetiole. Stenamma megamanni, in contrast, is always black, has a larger eye (8 or more ommatidia at greatest diameter), and usually has the postpetiole similar in size to the petiolar node. In addition, there seems to be some ecological separation between the species. Even though S. megamanni does occur at high elevation and in leaf litter, it is commonly found nesting at lower elevations in riparian areas. Nests have been found both in clay banks and under rocks along streams. Stenamma manni nests have never been found in these environments. It could be that S. megamanni is an ecomorph of S. manni, but both species have been found together in samples of leaf litter. Molecular phylogenetic data so far show that S. megamanni forms a clade nested within the larger S. manni complex. Branstetter (2013) hypothesizes that S. manni and possibly S. megamanni, include more than one species, making it difficult to adequately separate each at a wide regional scale.
As a preface to describing each variant of S. manni, Branstetter (2013) has noticed several phenotypic trends within the complex that correlate with habitat. Populations from drier areas, especially those from central and western Mexico, tend to be lighter in color, have more developed sculpturing, and have denser pilosity, with the lower layer of gastral pilosity often pubescent. In contrast, specimens from wet forest environments are often shinier and less sculptured and have sparser pilosity. They also tend to be darker in color, but not always.
Characteristics of the type population (CASENT0126265) are indicated within the worker and queen descriptions of Bransetter (2013). It is important to note that although these specimens now appear brown in color, the original description says that they were black, with the tarsi, leg joints, and tips of the mandibles and antennae dark red. Overall, these specimens seem to be rather average looking in size, sculpture, and pilosity, compared with many other S. manni populations. Only the eyes seem somewhat large relative to head size. Most other S. manni populations have one or more characters exaggerated in some way. Another important observation is that these specimens were collected from between 3050–3350 m under a rock in pine forest. This is very high for tropical ants in general, and is one of the highest records for Stenamma. The only report of Middle American clade Stenamma from a higher elevation is from 3700 m at the locality Rancho Somecla on Pico de Orizaba in Veracruz, Mexico. These specimens are also S. manni and they are the most similar in morphology to the type population. It should be noted that in color and eye size, the type population might appear more similar to S. megamanni than some of the variants below. However, specimens from the type population are much smaller than S. megamanni and the sculpture and pilosity are different. Also, I see intermediate forms within Mexico that seem to connect the type population with the other variants.
Variant 1 (CASENT0604893) is the form that co-occurs with S. megamanni in Central America. It has been collected from Chiapas, Mexico, to Nicaragua, and as mentioned above, can be distinguished by its dark red-brown coloration, smaller eye, and bulging postpetiole, which is usually distinctly larger than the petiolar node in profile view. It occurs almost exclusively above 2000 m. Some populations (e.g. Huitepec) have extremely large workers with allometrically enlarged scapes and metafemurs. Compared to the type population, these larger specimens look like giants. Among populations of this variant within Central America, there is considerable sculpture and size variation.
Variant 2 (CASENT0605527) is known only from the Atlantic slope of the Sierra Juarez Mountains between Oaxaca and Valle Nacional in Oaxaca, Mexico. All collections were above 1650 m in cloud forest habitat. Branstetter (2013) thinks of this variant as a high elevation, wet forest-adapted version of S. manni. Variant 2 is characterized by the fol- lowing: general body color brown to yellow-brown, mottled; face mostly smooth and shining, with only some faint carinulae extending back from frontal lobes; pronotum almost completely smooth and shiny; scape slender, somewhat elongate (SI 102–106); metafemur relatively elongate (MFI 82–83); propodeal spines well developed, short (PSL 0.13–0.17, PSI 1.4–1.6); anterodorsal margin of propodeum forming a distinct welt, causing the metanotal groove to appear deep; petiolar and postpetiolar nodes somewhat compressed anteroposteriorly; postpetiolar node enlarged, somewhat bulging; gastral pilosity indistinctly bilayered, with lower subdecumbent layer of setae sparse. The gestalt of this variant is most similar to variant 1. Both have the postpetiole more bulging, and the scape and metafemur longer. The shape of the propodeum in profile is also very similar. Confirming the similarity, molecular phylogenetic data show variant 2 being more closely related to a specimen of variant 1 from Chiapas, Mexico, than to specimens further north in Mexico (Branstetter unpublished data). It is important to note that this variant occurs in sympatry with S. leptospinum. Intriguingly, both share the anteroposteriorly compressed petiolar and postpetiolar nodes.
Variant 3 (CASENT0126280) occurs at Nevado de Colima in Jalisco, Mexico, with similar forms at other nearby sites. It seems to be a version of S. manni that is adapted to drier habitats. It is characterized by the following: eye somewhat small, with 6 ommatidia at greatest diameter; dorsum of promesonotum rugoreticulate; side of mesosoma strongly punctate; petiole and postpetiole completely sculptured, mostly punctate, with rugoreticulae on dorsal surfaces of nodes; posterior portion of petiole bent downward, creating a small concavity under node; first gastral sternite strongly punctate; first gastral tergite punctate, but punctae broader, more like small dents, and less dense than sternal punctae; pilosity on gastral dorsum distinctly bilayered, with a layer of long suberect setae, and a layer of very dense (almost pubescent) decumbent setae, dorsum of petiolar and postpetiolar nodes with similar pilosity. There is some evidence for sympatry at Nevado de Colima. Variant 3 was collected at 2070 m. A few specimens of a similar S. manni form were collected at 2440 m (same label as variant 3, but different elevation). These specimens do not have distinct rugoreticulae and the dense pubescence, but seem otherwise similar. Because of the difference in elevation between the specimens, the paucity of material, and the existence of intermediate specimens at other sites, Branstetter (2013) does not consider this potential sympatry as sufficient evidence for calling variant 3 a new species. However, Nevado de Colima would be a good site to visit to further study species boundaries in this complex.
Variant 4 (CASENT0605592) is known only from Pinal de Amoles, Querétaro, Mexico and is similar to variant 3. It could be a mesic forest version of variant 3, as it occurs in wetter oak-pine forest on the Atlantic slope of the Sierra Gorda. It is characterized by the following: general body color dark red-brown to brown; head noticeably broad and thick; eye small, with 5–6 ommatidia at greatest diameter; dorsum of promesonotum rugoreticulate-punctate, but rugoreticulae poorly developed on middle of dorsum, strongest on humeri; side of mesosoma strongly punctate; propodeal spines well-developed, somewhat robust, and distinctively shaped, being broad at the base and then curving outward, appearing somewhat hook-like; petiole noticeably elongate and bent downward at posterior margin; petiolar node in profile broad and subconical, reaching a defined apex; petiole and postpetiole almost completely punctate; first gastral sternite and tergite lightly punctate; pilosity on gastral dorsum somewhat dense, and clearly bilayered, with a layer of longer suberect to subdecumbent setae, and a layer of decumbent setae, both layers similar in density. Specimens with intermediate morphology between variant 3 and 4 occur in Oaxaca on the western, drier side of the state. Among these specimens there is variation in the development of punctae and pubescence on the gaster, which seems to be clearly linked with elevation. One population from 2350 m (15.5km NE Oaxaca) has no punctae on the first gastral sternite and reduced gastral pilosity. In all other respects it is identical to populations from lower elevations within the state.
Variant 5 (CASENT0194011) is known from a single collection in Jalisco, Mexico. It is characterized by two main features: pronotal dorsum and face densely rugoreticulate; pilosity on most of dorsal surface of mesosoma, waist, and gaster very dense, long, and flexuous. This variant is probably most similar to variant 3.
Variant 6 (CASENT0606975) is known from several sites in Guatemala (Cerro Carmona, Salama, Guatemala City), and Honduras (PN Celaque), ranging from 1500–2000 m approximately. It has the following distinctive features: head oval-shaped, somewhat narrow; pronotal dorsum rugoreticulate; side of pronotum punctate; body in profile appearing somewhat elongate and gracile; petiole long and gracile, node asymmetrical, with a long sloping anterior face and a short posterior face, dorsum usually pointing distinctly posteriad; postpetiole somewhat smaller than petiolar node, not bulging. This variant could be a distinct species. It occurs in sympatry with variant 1 of S. manni at Cerro Carmona and has been collected near S. megamanni. However, it is very rare (only ten specimens known), and no nests or queens have been found. Molecular phylogenetic data infer it to be closely related to variant 1 and S. megamanni. More sampling is needed to test its status.
Variant 7 (CASENT0622740) is known only from RN Datanlí El Diablo in Nicaragua. It is similar to variant 6, except as follows: pronotal sculpture mostly longitudinally carinulate, with a patch of smooth cuticle in middle of dorsum; pilosity more dense; setae on legs noticeably thickened and subdecumbent (best observed in dorsal view).
Variant 8 (CASENT0606002) is known from two specimens collected at almost 3000 m at the Sendero Ecologico La Maceta locality in Guatemala. It has the following distinguishing features: eye large, with 9 ommatidia at greatest diameter; pronotum mostly smooth, with some transverse carinulae; postpetiole similar in size to petiolar node; gastral pilosity sparse, and weekly bilayered. This variant is most similar to the type population, in terms of sculpture, body and eye size. Unfortunately, neither specimens from the type population, nor this variant have been included in phylogenetic analyses, so it is unclear how they are related. A few faded specimens from Tajumulco, Guatemala look similar.
Stenamma manni Wheeler, W. M. 1914: 51. Lectotype worker: MÉXICO, Hidalgo: on the trail between Real del Monte and El Chico, [ca. 20.138°N, 98.673°W], 10000-11000ft [3050–3350m], spring–summer 1913, pine forest, under large stone in damp spot (W. M. Mann) (MZC, Type 2 -3 8672, pin CASENT0126265, specimen furthest from pin) [examined]. Smith, 1962: 35, worker description. Branstetter, 2009: worker images. Branstetter, 2012: phylogeny. Branstetter, 2013: worker, queen descriptions and images; male images.
Stenamma mgb28 [variant 4 here] Branstetter 2012: phylogeny.
Branstetter, M. G. 2012. Origin and diversification of the cryptic ant genus Stenamma Westwood (Hymenoptera: Formicidae), inferred from multilocus molecular data, biogeography and natural history. Systematic Entomology 37:478-496. 10.1111/j.1365-3113.2012.00624.x.
Branstetter, M. G. 2013. Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae). ZooKeys 295:1-277. doi: 10.3897/zookeys.295.4905.
Found most commonly in these habitats: 247 times found in cloud forest, 31 times found in oak forest, 5 times found in oak-pine forest, 4 times found in forest, 5 times found in oak cloud forest, 1 times found in meadow, pine-oak cloud forest, 9 times found in cloud forest at night, 4 times found in disturbed cloud forest, 8 times found in hardwood forest, 2 times found in cloud forest w/bamboo, ...
Found most commonly in these microhabitats: 290 times ex sifted leaf litter, 63 times at bait, 6 times forest litter, 2 times nest in leaf litter, 2 times ex Odontoglossum grande, 3 times nest in soil and dead wood, 1 times nest under rock, 2 times nest in soil, 1 times foragers on log, 1 times ex Schomburgkia sp., 2 times ex ground, ...
Collected most commonly using these methods: 171 times MiniWinkler, 67 times maxiWinkler, 65 times Baiting, 26 times search, 24 times Berlese, 19 times Winkler, 17 times Berlese/Winkler, 3 times quarantine, 11 times Hojarasca berlese, 9 times Night MiniWinkler, 2 times Beating, ...
Elevations: collected from 220 - 3700 meters, 2254 meters average