Bioacoustics of Dubiaranea difficilis

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) .