Sericomyrmex opacus Mayr, 1865

Jesovnik, Ana & Schultz, Ted R., 2017, Revision of the fungus-farming ant genus Sericomyrmex Mayr (Hymenoptera, Formicidae, Myrmicinae), ZooKeys 670, pp. 1-109 : 63-72

Sericomyrmex opacus Mayr, 1865 Figures 43, 44(Worker); Figure 45(Queen and male); Figure 46(Larva); Figure 47 (Map)

Sericomyrmex opacus Mayr, 1865: 84. Lectotype worker (here designated): ( “Brazil”)* MEXICO, Veracruz, Córdoba, [18.8808, -96.9272], E. Norton (NHMW: 1w, CASENT0915956) Paralectotypes: Same data as lectotype: (NHMW: 1w, CASENT0915955) (USNM: 1w, USNM00924096).

Sericomyrmex aztecus = Forel, 1885: 363. syn. n. Type material examined: MEXICO, Veracruz, Orizaba, [18.85, -97.08], A. Forel (MSNG: 1w, CASENT0904987) (MHNG: 1w, CASENT0909368) (NHMW: 1w, USNMENT00924097).

Sericomyrmex diego = Forel, 1912: 192. syn. n. Type material examined: COLOMBIA, Magdalena, Don Diego, [11.23, -73.7], A. Forel (USNM: 1w, USNMENT00529165; 2w, USNMENT00921744) (BMNH: 2w, CASENT0901678) (MSNG: 2w, CASENT0904988; 1m, USNMENT00924098) (MHNG: 3w, CASENT0909369).

Sericomyrmex zacapanus = Wheeler, 1925a: 54. syn. n. Type material examined: GUATEMALA, Zacapa, [14.9722, -89.5306], 15 Dec 1911, W. M. Wheeler, (MCZ: 3w, USNMENT00924099; 2w, USNMENT00924100; 3w, USNMENT00924101) *For a discussion of the type locality of S. opacus see the notes section.

S. opacus worker diagnosis.

Small species; mandible smooth, glossy; posterior cephalic corner smoothly rounded; frontal lobe rectangular; eye small, often with at least partial white layer; mesosomal tubercles low, reduced; first gastral tergite with lateral carinae weakly developed, dorsal carinae absent.

S. opacus worker description.

Measurements in mm, range (lectotype): HWe 0.8-1 (0.93) HW 0.8-1 (0.95) HW1 0.78-1 (0.84) HW2 0.88-1.13 (0.96) HW3 0.54-0.74 (0.62) IFW1 0.54-0.73 (0.64) IFW2 0.16-0.28 (0.24) HL1 0.82-1 (0.9) HL2 0.6-0.9 (0.82) SL 0.58-1.08 (0.62) EL 0.12-0.18 (0.15) Om 6-10 (8) WL 0.99-1.3 (1.23) PL 0.2-0.33 (0.21) PPL 0.15-0.25 (0.18) GL 0.78-1 (0.87) HFL 0.68-1.02 (0.93) PW 0.50-0.72 (0.63) CI 95-106 (103) FLI 62-78 (69) SI 65-78 (67) OI 13-19 (16) CEI 5-19 (9) [N=68]

Pilosity. Pubescence dense, often lighter than integument, appressed to decumbent. Hairs curved, darker in color at base, yellow to gray, appressed to suberect, mostly decumbent.

Head. In full-face view almost equally broad and long (CI=100 ± 3), posterior corner smoothly rounded, posterior cephalic emargination relatively shallow (CEI=9 ± 2), gradually impressed. Vertexal impression and frontal tumuli faint. Mandibles with 7-8 teeth, dorsally smooth and glossy, finely transversely striate only along masticatory margin. Eye medium-sized (OI =16 ± 1), flat to slightly convex, 6-10 ommatidia across largest diameter, with (Figure 43a, 44d) or without (Figure 43b) thin white layer. Frontal lobe wide (FLI=70 ± 3), rarely triangular, mostly rectangular to trapeziform, posterior margin as long, or almost as long, as medial. Frontal carina usually incomplete, fading before reaching posterior cephalic corner. Antennal scape relatively short, never reaching posterior cephalic corner (SI=71 ± 2).

Mesosoma. Mesosomal tubercles small, low and obtuse. Propodeal carinae low and feeble, sometimes serrate, sometimes reduced to just posterodorsal denticles.

Metasoma. Petiole with two low, reduced denticles; postpetiole with two faint, short carina dorsally. First gastral tergite with lateral carinae weakly developed, dorsal carinae absent.

S. opacus queen description.

Measurements in mm, range: HWe 1.02-1.16 HW 1.05-1.20 HW1 1.10-1.25 HW2 1.20-1.30 HW3 0.72-0.85 IFW1 0.76-0.85 IFW2 0.24-0.33 HL1 1.09-1.12 HL2 0.98-1.00 SL 0.74-0.78 EL 0.20-0.24 Om 15-17 EW 0.08-0.10 WL 1.58-1.80 PL 0.34-0.48 PPL 0.24-0.28 GL 1.50-1.64 HFL 0.99-1.28 PW 0.90-0.96 FWg 4.85-5.17 HWg 3.60-3.64 CI 93-106 FLI 71-76 SI 64-73 OI 18-22 [N=6]

Head. Mandible with 7-8 teeth, dorsally glossy and smooth, finely transversely striate only along masticatory margin. Preocular carina fading posterior to eye, 1-3 isolated, short, thin, supraocular carinae sometimes present, never reaching posterior cephalic corner. Eye large (OI=20 ± 1), convex, 15-17 ommatidia across largest diameter. Frontal lobe as in worker, antennal scape not reaching posterior cephalic corner.

Mesosoma. Lateral pronotal tubercles low and obtuse. Scutum in dorsal view with notauli and median mesoscutal line reduced, parapsidal lines thin. Scutellum small and short, with posterior notch shallow to absent and with median impression sometimes separating scutellum in two lateral halves. Propodeal carinae low, each with low posterodorsal denticle.

Metasoma. Petiole with two dorsal and two lateral low and obtuse denticles, best seen in frontodorsal view. Postpetiole with two short, low carinae dorsally and two low denticles laterally. First gastral tergite with lateral carinae well developed, dorsal carinae absent, anteromedian groove visible.

S. opacus male description.

Measurements in mm, range: HWe 0.66-0.74 HW 0.46-0.58 IFW1 0.20-0.27 IFW2 0.13-0.18 HL1 0.53-0.61 SL 0.49-0.62 EL 0.22-0.28 Om 19-28 EW 0.09-0.14 WL 1.20-1.44 PL 0.27-0.38 PPL 0.16-0.22 GL 0.96-1.12 HFL 1.20-1.50 PW 0.50-0.80 IOD 0.36-0.50 FWg 3.48-4.10 HWg 2.20-2.84 CI 115-125 FLI 30-38 SI 71-88 OI 29-39 [N=7]

Head in full-face view longer than broad (CI=121 ± 4). Eye large (OI=34 ± 3), convex, 19-28 ommatidia across largest diameter. Preocular carina fading posterior to eye, medially curved before fading. Notauli and mesoscutal line faint, parapsidal lines thin, groove between axillae smooth, sometimes weakly transversely costate. Propodeum without denticles or carinae. Petiole and postpetiole with lateral denticles very reduced, dorsal denticles absent.

S. opacus larva description.

Approximately eight setae on each side of dorsal and lateral body surfaces (i.e., approximately 16 total). Supra-antennal setae absent. Four genal setae on each side. Mandibular apical tooth undivided. Labial denticles not visible. First thoracic segment ventrally with multiple multidentate spinules, arranged in trans verse rows. Numbers of ventral hairs: six on each thoracic segment, eight on the abdomen (not including anal setae). Single pair of sensilliform setae anterior to anal opening.

S. opacus geographic range.

Brazil, Central America, Colombia, Mexico. Map: Figure 47.

S. opacus notes.

The species most similar to S. opacus are S. parvulus , S. saramama , and, in Central America, smooth-mandibled populations of S. amabilis . Typical amabilis can be distinguished from opacus by their completely striate mandibles, triangular frontal lobes, and larger size. The distinction between opacus and smooth-mandibled amabilis is less obvious, but the frontal lobes, head shape, and size are still good indicators. An ameliorating factor for this difficulty is that, when sympatric, amabilis and opacus are very distinct; we have not encountered the smooth-mandibled amabilis variant sympatric with opacus , which might indicate character displacement. The queen of S. opacus can easily be separated from that of the sympatric S. amabilis by its smaller size, smooth mandibles (striate in amabilis ), and usually less conspicuous notauli on the scutum. The main characters separating S. opacus from saramama are the shape of the frontal lobes (triangular in saramama ) and the white layer over the eyes (absent in saramama ). The S. saramama queen can easily be separated from the opacus queen by its striate mandibles (smooth in opacus ).

S. parvulus can be distinguished from the typical opacus by having smaller, narrower, triangular frontal lobes; smaller overall size; and shorter frontal carinae, often fading well before reaching the posterior cephalic corners. Separating non-typical representatives of opacus , which may also have reduced frontal lobes, from parvulus is difficult. Also, it is very difficult to separate queens of opacus and parvulus . The parvulus queen is slightly smaller and lacks the faint supraocular carinae; however, these carinae are absent in some opacus queens as well. The region of overlap of the known distributions of these two species is limited, so geographic origin can aid in species identification (Figure 47).

S. opacus is morphologically variable across its geographic range. This variation is correlated with patterns in the molecular phylogeny (Suppl. material 1) as well as with geography. The three main subspecific geographical and molecular subclades, all reciprocally monophyletic, are: Central American (population opacus 1), North Colombian (population opacus 2), and South Colombian and West Brazilian (population opacus 3). The most pronounced variation within opacus occurs in the shape of the frontal lobes and in the eyes. The typical S. opacus has rectangular frontal lobes and the eyes covered with a thin white layer. In populations of opacus 1 there are occasional, rare individuals with smaller, almost triangular lobes and eyes lacking the white layer. These rare, odd specimens are also smaller in size, so these atypical character states could be correlated with size (e.g., in nanitic workers). The specimens from opacus 2 populations, from Northern Colombia, are fairly uniform, typical representatives of the species. This uniformity, however, may be an artifact of our small sample size (20 individuals). Most opacus 2 specimens were collected in pitfall traps, so no nest series were available for evaluating within-nest variation. The specimens from the opacus 3 population all have eyes lacking the white layer and the frontal lobes are often (but not always) more triangular than rectangular. The number of samples available from this population is also low (19 specimens examined compared to 97 for opacus 1) and there are a few specimens from this population that are morphologically typical, including individuals with rectangular frontal lobes. The principal component analysis of the morphological data for just these three opacus populations (Figure 5f) shows no separation of the three populations along the two main axes. With regard to the high degree of morphological variation in S. opacus , one possibility well worth considering is that opacus and parvulus (which are similar in size and which overlap in distribution in the area where opacus 3 occurs) can hybridize (Figure 47). If so, then the specimens that are difficult to identify as either parvulus or opacus could be opacus - parvulus hybrids. Separate PCA analysis of only parvulus and opacus indicates a large amount of overlap (Figure 5b) along the two main axes. The data currently available are insufficient for recognizing the three opacus subclades as species and we believe that the observed pattern (especially in opacus 3) is likely an artifact of our low sample sizes. It is entirely possible that further sampling, especially of whole-nest series, might reveal that S. opacus actually consists of multiple species and/or that opacus hybridizes with parvulus .

S. opacus type locality. The original description of S. opacus by G. L. Mayr in 1865, which is also the original description of the genus Sericomyrmex , lists “Brasilien” as the type locality. Based on the route of the Novara-Expedition, which is the expedition from which Mayr’s specimens supposedly originated, the Brazilian type locality is most likely Rio de Janiero (Mayr, 1865). However, the locality labels of the type specimens (CASENT0915955, CASENT0915956, USNMENT00924096) of Sericomyrmex opacus that we studied indicate "Mexico, Cordoba," and “Norton” as the collector. The labels look original when compared to the labels of other Mayr type specimens, both in terms of handwriting and in resemblance to the labels of other specimens collected by Norton. Indeed, Mayr described other species based on specimens collected by E. Norton in Mexico, so he clearly had access to Norton’s Mexican material. Importantly, the type specimen of S. opacus is identical to the type specimen of S. aztecus , a Mexican species described by Forel (1885), which in turn is identical to numerous specimens collected in Mexico and elsewhere in Central America. S. aztecus is the name most commonly applied to such specimens. Given these facts, the most likely explanation is that the locality of the type specimen of S. opacus ( “Brasilien”) given in the original description is incorrect and that the locality labels affixed to the syntype specimens are correct. The alternative explanation is that the published locality is instead correct, the specimen labels are incorrect, and that the type specimen of S. opacus originated in Brazil. We judge this alternative to be highly unlikely, because S. opacus (under which we have synonymized S. aztecus , S. diego , and S. zacapanus ) does not occur anywhere near Rio de Janeiro (Figure 47).

Synonymies.

The type specimens of S. aztecus , S. diego , and S. zacapanus all possess typical opacus morphology, including the rectangular frontal lobes. In his description of zacapanus Wheeler (1925a) mentions that it is smaller in size than diego , but our measurement data indicate that the cited difference is very small (Suppl. material 2: Table S2a) and falls entirely within the size variation of the species. In his description of aztecus Forel (1912) indicates that it has a relatively smooth petiole, whereas in opacus dorsal denticles are present. Variation in petiolar and postpetiolar carinae and denticles is not diagnostic for species of Sericomyrmex , and those characters often vary within a single colony.

S. opacus material examined.

BRAZIL: Amazonas: São Gabriel de Cachoeira ( Uapés), [-0.1237, -67.0476], 120m, 23 Aug 1992, T. R. Schultz; Rondônia: Ilha do Bufalo, km 0.5, -9.2656, -64.2125, 90m, 19 Jan 2014, I. O. Fernandes; Jaci MD, km 3, -9.2656, -64.2125, 94m, 22 Jan 2014, I. O. Fernandes; Jaci-Paraná, km 2, -9.2656, -64.2125, 94m, 6 Jun 2012, I. O. Fernandes; Novo Modulo, Jaci-Paraná, km4, -9.4630, -64.3911, 122m, 24 Jan 2014, I. O. Fernandes; COLOMBIA: Amazonas: PNN Amacayacu Matamata, -3.6833, -70.25, 150m, 20 May 2000, A. Parente; PNN Amacayacu, -3.8103, -70.2662, 88m, 7 Oct 2007, J. Sosa-Calvo, J. Rodriguez; Bolívar: PNN Los Colorados, Villa Roca, 9.9, -75.1166, 180m, 26 May 2001, E. Deulufeut; PNN Los Colorados, La Yaya, 9.9, -75.1166, 280m, 21 Jul 2001, E. Deulufeut; PNN Los Colorados, Alto el Mirador, 9.9, -75.1166, 400m, 11 Apr 2001, E. Deulufeut; PNN Los Colorados, Venado, 9.9, -75.1166, 320m, 1 Jan 2001, E. Deulufeut; Putumayo: PNN La Paya Cabaña Chagra, -0.1166, -74.9333, 320m, 1 May 2002, R. Cobete; PNN La Paya Cabaña La Paya Chagra, -0.0333, -75.2, 330m, 26 Feb 2002, R. Cobete; PNN La Paya Cabaña La Paya, -0.0333, -75.2, 330m, 2 Jul 2002, R. Cobete; PNN La Paya Cabaña Viviano, -0.1166, -74.9333, 320m, 26 May 2002, A. Morales; PNN La Paya Río Caucaya, -0.1166, -74.9333, 330m, 15 Oct 2001, R. Cobete; COSTA RICA: Guanacaste: Canas, Finca Pacifica, [10.42, -85.10], 16 Jul 1986, S. B. Peck; Hacienda La Pacifica, nr. Canas, 10.24, -83.80, 50m, 1 May 1979, P. S. Ward; PN Santa Rosa, [10.8378, -85.7051], 14 Jun 1995, U. G. Mueller; Puntarenas: Osa Peninsula, Corcovado, Sirena Station, Pavo trail, [8.51, -83.60], 2 Jun 1992, T. R. Schultz; ECUADOR: Esmeraldas: 10 km S Atacames, [0.7755, -79.8462], 205m, 7 Nov 1987, C.R.F. Brandão, C.D. Bastidas; Los Ríos: Río Palenque Research Station, [-0.583, -79.367], 20 Dec 1980, S. Sandoval; GUATEMALA: Retalhuleu: El Asintal, 14.6524, -91.73901, 670m, 30 Jul 2013, K. Delgado; Nuevo San Carlos, 14.6388, -91.72193, 585m, 9 Nov 2008, K. Delgado; HONDURAS: Copán: Copán Ruinas, 14.8379, -89.1428, 629m, 4 Jan 2008, C. Rabeling; Francisco Morazán: Esc. Zamorano, 14.0134, -87.0076 ± 25m, 800m, 19 May 2009, J. T. Longino; MEXICO: Chiapas: 8km SE Salto de Agua, 17.5143, -92.2949 ± 200m, 70m, 16 Jun 2008, M. G. Branstetter; San Luis Potosí: Cuesta de los Cedros, 36 km E of Ciudad del Maíz, [22.3889, -99.2515], 685m, 12 Jun 1962; Veracruz: Ocotal Chico, [18.2588, -94.8619], 579m, 26 Jun 1963, G. N. Ross; NICARAGUA: Masaya: Masatepe, vic. San Marcos, Cafetal San José del Llano, 11.917, -86.25, 485m, 23 Jun 1992, T. R. Schultz; Río San Juan: Río San Juan, Isla de Diamante, [10.9794, -84.3415], 9 Oct 1994, J. P. Caldwell; PANAMÁ: Colón: Gamboa, PN Soberanía, Pipeline Rd. Km 6, 9.08, -79.66, 24 Apr 1996, T. R. Schultz, U. G. Mueller; San Lorenzo Forest R1, 9.2833, -79.9666, 30 Dec 2004, A. Dejean, J. Orivel, B. Corbara, H. Aberlenc, M. Leponce; Panamá: Barro Colorado Island, Canal Zone, 9.15, -79.84, 1 Nov 1941, J. Zetek; El Llano-Carti Suitupo Rd, ca. 6km ex El Llano, [9.22, -78.97], 27 Apr 1996, T. R. Schultz, U. G. Mueller, S. Rehner.