Sericomyrmex amabilis Wheeler, 1925b

Jesovnik, Ana & Schultz, Ted R., 2017, Revision of the fungus-farming ant genus Sericomyrmex Mayr (Hymenoptera, Formicidae, Myrmicinae), ZooKeys 670, pp. 1-109 : 30-37

Sericomyrmex amabilis Wheeler, 1925b Figures 17, 18 a–d (Worker); Figures 18 e–j, 19(Queen and male); Figure 20(Larva); Figure 21 (Map)

Sericomyrmex amabilis Wheeler, 1925b: 166. Lectotype worker (here designated): PANAMÁ, Panamá, Barro Colorado Island, [9.1543, -79.8461], 3 Aug 1924, W. M. Wheeler, WMW838 (USNM: 3w, USNMENT00920034, topmost specimen on the pin). Paralectotypes: Same data as lectotype (USNM: 2w, USNMENT00920034, lower two specimens on the pin) (MCZ: 2w, 1q, MCZ40-42 21197).

Sericomyrmex bierigi = Santschi, 1931: 279. Type material examined: PANAMÁ, Chiriquí, La Concepción, 16 Jul 1930, Bierigi, (NHMB: 1w, CASENT0912515) [image examined]. Weber 1958: 263: junior synonym of amabilis .

S. amabilis worker diagnosis.

Medium-sized species; mandible usually striate; frontal carina complete; frontal lobe triangular; eye almost flat, without white layer; posterior cephalic margin with abrupt to gradual emargination; mesosomal tubercles from low and obtuse to well developed; first gastral tergite with lateral carinae strongly developed, dorsal carinae from weak to well developed.

S. amabilis worker description. Measurements in mm, range (lectotype): HWe 0.88-1.21 (1.15) HW 0.88-1.24 (1.15) HW1 0.82-1.18 (1.12) HW2 0.92-1.36 (1.2) HW3 0.58-0.9 (0.75) IFW1 0.56-0.86 (0.78) IFW2 0.19-0.35 (0.3) HL1 0.82-1.2 (1.05) HL2 0.76-1.04 (0.93) SL 0.65-0.87 (0.76) EL 0.11-0.2 (0.162) Om 7-11 (8) WL 1.13-1.6 (1.44) PL 0.22-0.4 (0.3) PPL 0.16-0.29 (0.24) GL 0.78-1.12 (1.03) HFL 0.93-1.38 (1.21) PW 0.58-0.92 (0.78) CI 97-111 (110) FLI 60-72 (68) SI 66-78 (66) OI 12-19 (14) CEI 5-15 (10) [N=70]

Pilosity. Pubescence dense, often lighter colored 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 slightly broader than long (CI=104 ± 3, mean ± SD), posterior corner rounded to angular. Posterior cephalic margin with distinct median emargination (CEI=10 ± 2), gradually (Figure 7j) or abruptly (Figure 7k) impressed. Vertexal impression and frontal tumuli usually distinct. Mandible with 7-9 teeth, dorsally glossy and striate, striation sometimes reduced. Eye medium-sized (OI=16 ± 1), flat to slightly convex, 7-11 ommatidia across largest diameter. Frontal lobe triangular, posterior margin shorter than medial, lobe diverging laterally, relatively wide (FLI=68 ± 2). Frontal carina complete, reaching posterior cephalic corner. Antennal scape relatively short, never reaching posterior cephalic corner (SI=71 ± 3).

Mesosoma. Mesosomal tubercles from low and obtuse to well developed. Propodeal carinae low, sometimes serrate, each with low posterodorsal denticle.

Metasoma. Petiole and postpetiole each with pair of low, serrate carinae dorsally; in petiole sometimes reduced to two low denticles, seen in dorsolateral view. Postpetiole with another pair of low carinae laterally, sometimes reduced to low denticles. First gastral tergite with lateral carinae strongly developed, dorsal carinae faint in most specimens, sometimes strongly developed.

S. amabilis queen description.

Measurements in mm, range: HWe 1.27-1.40 HW 0.34-1.45 HW1 1.30-1.52 HW2 1.40-1.52 HW3 0.87-1.04 IFW1 0.90-1.00 IFW2 0.27-0.37 HL1 1.27-1.45 HL2 1.15-1.25 SL 0.81-0.99 EL 0.23-0.29 Om 15-22 EW 0.06-0.1 WL 1.95-2.2 PL 0.45-0.58 PPL 0.28-0.4 GL 1.68-1.87 HFL 1.16-1.58 PW 1.05-1.52 FWg 5.85-6.93 HWg 3.79-4.41 CI 93-104 FLI 70-77 SI 62-74 OI 18-22 [N=10]

Head. Mandible with 8-9 teeth, dorsally glossy and striate. Preocular carina usually fading posterior to eye. Eye large (OI=20 ± 1), nearly flat, 15-22 ommatidia across largest diameter. Frontal lobe as in worker, antennal scape not reaching posterior cephalic corner.

Mesosoma. Scutum in dorsal view with notauli weak, median mesoscutal sulcus reduced. Groove between axillae in dorsal view sometimes weakly transversely costate. Scutellum slightly convex in profile view, narrowing posteriorly in dorsal view, posterior margin medially with wide shallow V-shaped notch, notch sometimes continuing into median impression that divides scutellum into two lateral parts. Propodeum in dorsal view with two low carinae, each with posterodorsal denticle.

Metasoma. First gastral tergite with lateral carinae well developed, dorsal carinae absent, anteromedian groove distinct.

S. amabilis male description.

Measurements in mm, range: HWe 0.61-0.98 HW 0.6-0.78 IFW1 0.24-0.48 IFW2 0.17-0.25 HL1 0.61-0.78 SL 0.59-0.76 EL 0.24 0.35 Om 20-26 EW 0.1-0.18 WL 1.43-2.02 PL 0.25-0.43 PPL 0.18-0.25 GL 1.08-1.75 HFL 1.48-1.95 PW 0.58-0.90 IOD 0.54-0.63 FWg 4.28-5.77 HWg 2.68-3.68 CI 100-129 FLI 33-60 SI 74-99 OI 34-40 [N=10]

Head in full-face view longer than broad (CI=120 ± 7). Eye large (OI=38 ± 2), 20-26 ommatidia across largest diameter. Preocular carina slightly curved medially, fading posterior to eye. In dorsal view, scutum with notauli well developed, mesoscutal line faint, groove between axillae with up to four transverse costae. Propodeal carinae short and faint. Petiole with lateral and dorsal denticles, postpetiole with very reduced lateral denticle.

S. amabilis larva description.

About 15 setae on each side of dorsal and lateral body surfaces (i.e., total ~30). Supra-antennal setae present. Four genal setae on each side. Mandibular apical tooth divided. Labial denticles present anterior to sericteries, sparse. First thoracic segment ventrally with multiple multidentate spinules, arranged in transverse rows. Numbers of ventral setae: six on T1, four on T2, four on T3, and around ten on abdomen (not including anal setae). Single pair of setae anterior to anal opening.

S. amabilis geographic range.

Central America, Colombia, Ecuador, Mexico, Venezuela. Map: Figure 21.

S. amabilis notes.

S. amabilis differs from the sympatric S. opacus by its larger size, striate mandibles (in opacus always smooth), triangular frontal lobes (rectangular in opacus ), the shape of the posterior cephalic corners (in opacus smoothly rounded), and the presence of dorsal carinae on the gaster. The differences in size and mandibles also help in separating queens of these two species. In addition, the notauli and mesoscutal line are often pronounced in amabilis and faint or absent in opacus , although this can vary in both amabilis and opacus .

S. amabilis can be separated from its sister species S. saussurei by its flatter, uncoated eyes (convex, with a thick white layer in saussurei ) and usually by geography (Figure 21). It can be separated from S. mayri by its smaller size, narrower head, complete frontal carinae, and wider frontal lobes.

Within S. amabilis , there is variation in the character of smooth versus striate mandibles. In the majority of specimens examined for this revision (including the type specimens) the mandibles are consistently striate across the entire dorsal surface (Figure 17a). In some populations, however, some specimens from a given locality have striate mandibles and some have completely smooth mandibles (Figure 17b). In those populations intermediate forms are also found, with faint striations most obvious along the posterior lateral edge of the mandible.

The population of amabilis at Costa Rica, Heredia, La Selva Biological Station, exemplifies the polymorphic state in which both smooth and striate mandibles co-occur, whereas the population from Costa Rica, Puntarenas, Osa Peninsula, contains only the striate state. A few specimens from Nicaragua and Ecuador also have smooth or faintly striate mandibles. Specimens of amabilis from Gorgona National Park (an island 35 km off the Pacific coast in the department of Cauca, Colombia) show the complete range of variation, from fully striate through intermediate to completely smooth mandibles. We did not find both forms, fully striate and completely smooth, co-occurring within a single nest, but we examined nest series from only a few localities. The smooth-mandibled populations do not form distinct clusters in molecular phylogenies of amabilis ; rather, smooth-mandibled specimens group with striate-mandibled ones and vice versa. Likewise, statistical analyses of morphological measurements do not identify any distinct clusters correlated with mandibular sculpture (Figure 5e).

Members of the Gorgona population of amabilis have longer and sharper lateral mesonotal tubercles and more robust anteromedian dorsal carinae on the gaster compared to Central American populations. Some specimens from Nicaragua have a thin, translucent white layer covering part of the eye, similar to the condition observed in S. opacus . Other variable characters in amabilis are the frontal carinae (usually complete, but less developed in some), head shape (from angular to more rounded posterior head corners), and the size of the frontal lobes.

A single sequenced specimen from the population of S. amabilis from Venezuela (indicated with a yellow circle in the Figure 21) is molecularly distinct from the rest of the amabilis clade, as indicated by its position in the molecular phylogeny of Sericomyrmex (Suppl. material 1). This specimen, referred to as S. amabilis VE, is the sister of a clade that contains two reciprocally monophyletic subclades: (i) the monophyletic S. saussurei and (ii) all S. amabilis except S. amabilis VE. The molecular phylogeny, based on UCEs, reconstructs S. amabilis VE as a separate, third, species-level lineage ( Ješovnik et al, 2017). The two available specimens, however, are morphologically identical to the specimens assigned to amabilis . Because of the small number of specimens and the lack of distinguishing morphological data, and because the molecular data are consistent with a scenario in which S. saussurei arises from within a paraphyletic S. amabilis , we are for now treating S. amabilis VZ as an allopatric population of amabilis that renders amabilis paraphyletic. We would like to encourage further study of this population and more thorough sampling in Venezuela in general, which will hopefully bring more insight into the species status of this population.

S. amabilis material examined.

COLOMBIA: Antioquia: Amalfi Cañon del Río Porce, El Caiman, 6.8572, -75.0958, 970m, 19 Dec 1999, E. Vergara, F. Serna; Cauca: PNN Gorgona Alto El Mirador, 2.9666, -78.1833, 180m, 21 Oct 2000, R. Duque; PNN Gorgona Antigua Laguna, 2.9666, -78.1833, 70m, 20 Dec 2000, R. Duque; PNN Gorgona El Helechal, 2.966, -78.1833, 30m, 17 Mar 2002, R. Duque; PNN Gorgona El Roble, 2.9666, -78.1833, 120m, 17 Jun 2001, R. Duque; PNN Gorgona El Samán, 2.9666, -78.1833, 5m, 14 Sep 2001, H. Torres; PNN Gorgona Mancora, 2.9666, -78.1833, 60m, 20 Dec 2000, R. Duque; Cundinamarca: Melgar to Girardot, [4.249, -74.726], 28 Mar 1967, R. B. Root, W. L. Brown; Magdalena: 4 km N San Pedro, 10.95, -74.05, 220m, 14 Aug 1985, P. S. Ward; Meta: San Martín Caduceo, [3.6970, -73.6982], 400m, 4 May 2006, J. Ordonez; Valle del Cauca: Buenaventura, Bajo Calima, Villa Clara, [3.996, -76.974 ± 2000m], 30m, 18 Mar 1967, R. B. Root, W. L. Brown; PNN Farallones de Cali, Anchicayá, 3.4333, -76.8, 730m, 1 Jul 2000, S. Sarria; COSTA RICA: Heredia: La Selva Biol. Station, 10.43, -84.017, 50-150m, 1 Aug 2004, J. Sosa-Calvo; Limón: Puerto Viejo, [10.51, -84.18], 18 Jun 1979, J. Paich; R. Toro Amarillo Vic., Guapiles, 10.2166, -83.7667, 25 Feb 1966, W. L. Brown; Puntarenas: 15 km SSW Puerto Jiménez, [8.4083, -83.3278 ± 30m], 170m, 7 Mar 2010, J. T. Longino; Osa Peninsula, Corcovado, Sirena Station, 8.50, -83.6166, 31 May 1992, T. R. Schultz; ECUADOR: Esmeraldas: Las Vegas, 0.7547, -79.8490, 26 Jun 2003, A. G. Himler; Loja: Reserva Jorupe, Macará, -4.372, -79.906, 600m, 15 Sep 2011, T. Delsinne; Los Ríos: Río Palenque, 2km SSE Patricia Pilar, -0.5833, -79.3666, 160m, 1 Sep 1991, M. J. Stern; Río Palenque Research Station, 47 km S Santo Domingo [-0.583, -79.367], 28 May 1905, S., J. Peck; Napo: Limoncocha, -0.4, -76.6, 250m, 18 Jun 1976, S., J. Peck; Tiputini, La Selva, Chorongo trail, -0.4975, -76.3747, 12 Jun 2003, A. Little; GUATEMALA: Escuintla: Escuintla, [14.2445, -90.7995], 22 Sep 2008, W. M. Mann; Izabal: 16 km ESE Morales, 15.4111, -88.7118 ± 58m, 440m, 19 May 2009, J. T. Longino; 5 km NW Morales, 15.5097, -88.8627 ± 36m, 160m, 18 May 2009, J. T. Longino; Petén: Cerro Cahui, 17.0023, -89.7194, 210m, 3 Feb 2009, Llama team; Retalhuleu: El Asintal, 14.6555, -91.7344, 720m, 19 Feb 2013, K. Delgado; Nuevo San Carlos, 110 km NW Retalhuleu, 14.6258, -91.7234, 440m, 27 Feb 2013, K. Delgado; San Felipe, 14.6309, -91.581, 745m, 8 Feb 2013, K. Delgado; HONDURAS: Gracias a Dios: Las Marias, 15.6817, -84.8352 ± 20m, 80m, Llama team; Olancho: 14 km WSW Catacamas, 14.7997, -86.0141 ± 210m, 600m, 13 May 2009, J. T. Longino; MEXICO: San Luis Potosí: Río Santa Maria, Tamul, 21.8025, -99.1803, 200m, 2 Jul 1992, S. Sanchez-Pena; Veracruz: Catemaco, Tuxtla, 18.5865, -95.0779, 184m, 3 Oct 2013, A. Ješovnik; Ocotal Chico, 18.2588, -94.8619, G. N. Ross; NICARAGUA: Matagalpa: Pancasan, nr. Río Guapotal, 12.92, -85.55, 450m, 17 Jun 1992, T. R. Schultz, J. C. Gomez; Selva Negra, ca. 12 km N Matagalpa, Reserva Natural Cerro El Arenal, 12.9812, -85.9136, 1009m, 28 Dec 2007, C. Rabeling; Región Autónoma del Atlántico Norte: PN Cerro Saslaya, 13.7705, -84.9789 ± 20m, 290m, 7 May 2011, M. G. Branstetter; Región Autónoma del Atlántico Sur: RN Kahka Creek, 12.6851, -83.7136, 50m, 8 Jun 2011, M. G. Branstetter; PANAMÁ: Colón: Fort Sherman, 9.36, -79.95, 28 Apr 1996, T. R. Schultz, U. G. Mueller, S. Rehner; Gamboa, PN Soberanía, Pipeline Rd. ca. 2 km past Río Frijoles, 9.1205, -79.7067, 54m, 25 May 2002, C. J. Marshall; Gatún, Punta da los Chivos, 3 km SW Gatún, [9.26, -79.91], 1 Jul 1979, W. L. Brown; Mt. Hope, nr. Colón, 9.2833, -79.9667, 24 Jul 1924, W. M. Wheeler; San Lorenzo Forest, 9.2833, -79.9666, 25 May 2004, R. K. Didham; Darién: Cana, 7.7166, -77.7, 800m, 23 Aug 1987, D. M. Olson; Panamá: Barro Colorado Island, 9.15, -79.84, 1 Aug 1946, J. Zetek; Gamboa, Pipeline Rd, ca. 2 km past Río Frijoles, 9.1205, -79.7066, 54m, 25 May 2002, C. J. Marshall; Nusagandi Biol. Stn, Markisgandi trail, [9.2848, -79.0280], 26 Apr 1996, T. R. Schultz; PN Soberanía, Plantation Rd., 9.08, -79.66, 4 May 2011, R. M. M. Adams; VENEZUELA: Carabobo: Mocundo, ca. Aguirre, [10.2533, -68.2683], 750m, 27 Dec 2010, J. Lattke.