Dubiaranea difficilis ( Mello-Leitão 1944 )

Rubio, Gonzalo D., Rodrigues, Everton N. L. & Acosta, Luis E., 2010, Description of the male of the spider Dubiaranea difficilis (Araneae: Linyphiidae), with new records and modeling of its potential geographic distribution, Zootaxa 2405 (1), pp. 55-62 : 57-59

Dubiaranea difficilis ( Mello-Leitão 1944)

( Figs. 1–6 )

Paranesticus difficilis Mello-Leitão 1944: 333 , figs. 19–20.

Dubiaranea difficilis: Millidge 1991: 52 , fig. 173.

Type material. Holotype female ( MLP 15980), ARGENTINA: Buenos Aires: General Guido (36º38'22''S, 57º47'24''W), February 1941, M. Birabén coll. (examined).

New records. ARGENTINA: Córdoba: La Falda (31º05'21''S, 64º27'42''W), 24 October 2008 (G. Rubio), 1 male ( MLP 17986) ; Huerta Grande , site 1 (31º04'38''S, 64º29'28''W), 02 May 2009 (G. Rubio), 1 female ( CDA 000.812) ; same loc., site 2 (31º04'52''S, 64º29'12''W), 09 May 2009 (same coll.), 3 females ( CDA 000.813), 06 September 2009 (same coll.), 1 male ( CDA 000.816) . Jujuy: Potrero de Yala (24º07'13''S, 65º27'24''W), 29 November 2008 (M. Guerra & G. Rubio), 2 females ( CDA 000.814) ; Calilegua, Ríos Aguas Negras–San Lorenzo intersection (23º45'47''S, 64º51'01''W), 19 October 2009 (M. Pocco & G. Rubio), 1 female ( CDA 000.837) ; same loc., near Monolito (23º40'27''S, 64º54'01''W), same date (same coll.), 1 female ( CDA 000.838) . Salta: Posta de Yatasto (25º35'44''S, 64º57'09''W), 26-28 April 2006 (G. Rubio, J. Corronca, B. Cava, V. Olivo & A. González-Reyes), 1 female ( MLP 18017) ; Arroyo Las Tipas (25º24'37''S, 64º56'58''W), 01 August 2006 (same coll.), 1 female ( MLP 18018) ; Quebrada San Lorenzo : site 1 (24º43'16''S, 65º30'94''W), 01 August 2006 (same coll.), 1 male ( MLP 18019) ; La Caldera : site 1 (24º30'19''S, 65º19'61''W), 01 August 2006 (same coll.), 1 female ( MLP 18020) . San Luis: Merlo, Rincón del Este (32°20'51"S, 64°57'56"W), 10 January 2010 (M. Pocco & G. Rubio), 2 females ( CDA 000.817) and 2 male ( CDA 000.818) . Tucumán: Sierra de San Javier (26º48'04''S, 65º20'56''W), 24 November 2008 (G. Rubio) 1 female ( CDA 000.815) ; Parque Provincial El Cochuna (27º19'23''S, 65º55'40''W), 12 October 2009 (M. Pocco & G. Rubio) 3 females and 1 male ( CDA 000.839) .

Diagnosis: The male of D. difficilis ( Figs. 3, 4 ) resembles that of D. vetusta Millidge 1991 ( Millidge 1991: figs. 52, 53) and of D. fruticola Millidge 1991 ( Millidge 1991: figs. 80, 81) from Ecuador and Peru, respectively. It differs from both species in that the suprategulum of D. difficilis carries a small acute marginal suprategular apophysis ( Fig. 3 ), and the lamella characteristica presents a well developed mesal apophysis ( Fig. 4 ). The caudal apophysis of the lamella characteristica is slightly longer and slender than in D. fruticola , and the paracymbium tip is acute, not rounded as in D. vetusta . The female of D. difficilis is diagnosed by the scape of epigynum, which is broaden anteriorly and widened posteriorly, with a wide socket and wide atria ( Fig. 2 ; Millidge 1991: fig. 173).

Description. Male from La Falda, Córdoba (MLP 17986): Total length 4.16; carapace length 1.80; carapace width 1.27; clypeus height 0.32; sternum length 1.00; sternum width 0.84; abdomen length 2.30; abdomen width 0.77. Carapace low and elongated, pale yellowish-brown, with three blackish longitudinal bands starting at posterior eyes toward the posterior margin ( Figs. 5, 6 ). Cephalic region elevated, slightly separated from thoracic region by a V-shaped furrow immediately anterior to the groove ( Figs. 5, 6 ). Groove located in carapace posterior half. Eyes on shallow black tubercles ( Fig. 6 ); both rows of eyes recurved; the first row more than the second row; posterior median eyes almost twice larger than the lateral ones; anterior median eyes smaller than the rest; anterior lateral eyes and posterior lateral eyes touching ( Fig. 5 ). Sternum orange, truncated posteriorly. Chelicerae orange-brown, with about 20 stridulatory ridges; promargin with 3 teeth (the middle tooth much larger), and retromargin with 6 subequal teeth. Abdomen with parallel sides; ventrally dark grey; dorsally pale, with 3 blackish chevrons in the posterior half ( Figs. 5, 6 ), and with some lateral silver spots. Abdomen black distally. Legs yellowish (darker in the distal part of the tibiae), long and feeble, with some spines ( Fig. 6 ). Coxa III less developed. Position of Tm I 0.16. Legs I-III with one trichobothrium on each metatarsus, absent on metatarsus IV. Tibial spine formula: 2-2-2-2. Palpus with embolic membrane well developed; paracymbium relatively simple, robust distally; tegulum not well developed with sinuous edge, embolus long and filiform ( Figs. 3, 4 ).

Female (Holotype, MLP 15980): See Millidge (1991: 52).

Sexual dimorphism. Males and females differ only slightly in their somatic morphology. Females are slightly larger than males, mainly due to their larger and more globular abdomen. The cephalic/ocular region is somewhat higher in males than in females.

Variation. Males (n=4): Total length 3.80–4.62; carapace length 1.49–1.87; carapace width 1.10–1.28; sternum length 0.82–1.02; sternum width 0.62–0.85; abdomen length 2.20–2.56; abdomen width 0.77–0.95. Female (n=14): Total length 4.00–5.31; carapace length 1.54–1.90; carapace width 1.05–1.45; abdomen length 2.46–3.48; abdomen width 1.10–2.06. In both males and females, the dorsal coloration of abdomen may have pink-silvery spots.

Geographic distribution. Dubiaranea difficilis was only known from General Guido, which is the type locality ( Mello-Leitão 1944; Millidge 1991), and Reserva Natural Otamendi ( Grismado 2007), both in Buenos Aires province, Argentina ( Fig. 7 ). The 13 new records here provided revealed that D. difficilis has a much more extensive distribution indeed. This species has been recorded in three different sectors in Argentina: (1) the Pampean sector, comprising both the type locality and the record for Reserva Natural Otamendi, corresponding to the “Pampa Inundable” (flooding Pampas) and “Deltas e Islas del Paraná” ecoregions respectively ( Brown et al. 2006) (southeastern area in figure 7); (2) the central Sierras sector, with three records in the Sierras Chicas and one in the Sierras de Comechingones of Córdoba and San Luis Provinces respectively ( Fig. 7 ), bearing sierra Chaco vegetation; and (3) the northwestern sector, with most records corresponding to mountain forests and rainforests (Yungas eco-region), from Tucumán, Salta and Jujuy ( Fig. 7 ).

In the distribution model, the presence is set over the 0.213 logistic threshold, and the algorithm converged after 220 iterations. The potential range of D. difficilis under the model parameters is displayed in figure 7. The map shows that this species has a distribution potentially larger than the actual occurrences of Argentina, and suggests different probabilities from each sector. The model assigns the highest suitability in the northwestern sector, matching the Yungas area. Another sector with good probabilities corresponds to the Sierras de Córdoba. The Pampean sector shows low suitability in spite of having records. According to the model, the species might reach Tarija in Bolivia, and eastern São Paulo and southern Minas Gerais in Brazil ( Fig. 7 ). In general, the predicted range looks quite consistent with the expected distribution, considering the known records and the ecoregions involved. However, there is one meaningful region that is unlikely to be inhabited by the species, but is predicted by the model as present: the xeric valleys west of the Aconquija chain in Salta, Tucumán and Catamarca ( Fig. 7 ). Both sides of this mountain are markedly contrasting, the east-faced slopes bearing dense yungas vegetation, so these results should be taken with caution. It should be noted that the model assigns a similar low probability to extensive regions in the Pampas, among them the two sites in Buenos Aires Province with actual records.

The AUC evaluation values from 20 stochastic iterations ranged from 0.9777 to 0.9953 (mean = 0.9849); thus, individual and average AUC values resulted a high accuracy and good performance model. These values are comparable with performances obtained by Echarri et al. (2009), and Boubli & de Lima (2009).

Figures

FIGURE 1. Dubiaranea difficilis (Mello-Leitão 1944), male and female mating in nature; spiders are located in the sheet-web of the female. Left photo from La Falda, Córdoba (November 2008); right photo from Huerta Grande, Córdoba (September 2009).

FIGURE 2–6. Dubiaranea difficilis (Mello-Leitão 1944). 2. Female from Huerta Grande, Córdoba, 09 May 2009 (CDA 000.813), ventral view of epigynum. 3–6: Male from La Falda, Córdoba, 24 October 2008 (MLP 17986). 3. Left palpus, ectal view. 4. Left palpus, mesal view. 5. Habitus, dorsal view. 6. Habitus, lateral view. (C = abdominal chevrons; E = embolus; LC = lamella characteristica; CLC = caudal apophysis of LC; G = thoracic groove; MLC = mesal apophysis of LC; MSA = marginal suprategular apophysis; P = paracymbium; SPT = suprategulum). Scale bars: (2–4) 0.25 mm; (5, 6) 1 mm.

FIGURE 7. Locality records (yellow circles) and potential predictive range (blue colored areaa) of the spider Dubiaranea difficilis (Mello-Leitão 1944)(Linyphiidae) in Argentina (Northwest, central Sierras and Pampean sectors), Bolivia and Brazil. The arrow indicates the type locality. The darkest color indicates highest probability assigned by the MAXENT model (four intervals: 0.98–0.85; 0.85–0.60; 0.60–0.43 and 0.43–0.21). (BA = Buenos Aires Province; Co = Córdoba Province; Ju = Jujuy Province; Sa = Salta Province; SL = San Luis Province; Tu = Tucumán Province).