Oryctophileurus guerrai Perger & Grossi

Perger, Robert & Grossi, Paschoal Coelho, 2013, Revision of the rhinoceros beetle genus Oryctophileurus Kolbe with description of a new species, the male of O. varicosus Prell, and notes on biogeography (Scarabaeoidea, Dynastinae, Phileurini), ZooKeys 346, pp. 1-16 : 9-13

Oryctophileurus guerrai Perger & Grossi sp. n. Figs 7B, D; 8

Type material.

Holotype: male,"Bolivia / Tarija / O’Connor province / Tariquía National Reserve / S21°59' 01, W64°12' 30 / 1008 m a.s.l. / Tucuman-Bolivian subhumid forest / gully close to small mountain river / 25-XI-2011 / R. Perger leg." Allotype: female, same location data as the holotype, 20-XI-2011, F. Guerra leg.

Diagnosis.

Oryctophileurus guerrai sp. n. is distinguished from the morphologically similar Oryctophileurus armicollis by the distance between the inner teeth on the dorsal pronotal protuberance (in males as wide as width between eyes) (Figs 7B, 8A) and in females by the inner teeth separated by only a small fissure (Fig. 8C). In smaller males (body length 18.5 mm) of Oryctophileurus armicollis the distance between the inner teeth of the pronotal protuberance is wider than the width between the eyes and in larger males (body length 20 mm) as wide as the distance between the outer eye margins (Fig. 6A). In females of Oryctophileurus armicollis the inner teeth of the pronotal protuberance are separated by a comparably wide, continuous, parallel concavity containing ocellate punctures (Fig. 6C).

In both sexes of Oryctophileurus guerrai the ocellate punctures above the posteriolateral pronotal margin are smaller, shallower and sparser than in Oryctophileurus armicollis and the area of ocellate punctures above posteriolateral pronotal margin is reduced laterally (Figs 7D; 8B, D). In both sexes of other Oryctophileurus speciesthe pronotum posteriolaterally has a continuous area of distinctly developed, ocellate punctures.

In the male Oryctophileurus guerrai the pronotal protuberance is dorsally higher and the cephalic horn longer (Fig. 8B) than in similar-sized Oryctophileurus armicollis (Fig. 6B) and Oryctophileurus nasicornis (Fig. 3B). In Oryctophileurus nasicornis , both characters are less produced. In the male of Oryctophileurus varicosus (Fig. 4B), with its slightly larger body, the pronotum is much flatter than in the male of Oryctophileurus guerrai .

Description.

Holotype male (Figs 8A, B). Body length 20 mm, width 9 mm. Body elongate, cylindrical, head and pronotum brownish black dorsally, elytra black, body ventrally dark brown, dorsal surface glabrous. Legs, sterna, second abdominal ventrite and basal margin of pygidium setose.

Head. Surface smooth, finely punctate. Clypeus subtriangular, laterally emarginated, slightly upturned, and with acute apex. Cephalic horn recurving over pronotum, attenuate, apex narrowly rounded; surface at base coarsely punctate, with a lateral carina. Mandible tridentate with inner tooth more acute; teeth upturned. Antenna 10 segmented; club with antennomeres subequal in length.

Pronotum (Figs 7B, D; 8A, B). Shape subtrapezoidal, evenly rounded laterally, smooth, with 2 impressions posteriolaterally; posterior edges slightly obtuse. Basal half smooth, longitudinally ridged, dorsally bulging until transverse median carina, with 2 dorsolateral, coarsely punctate concavities on both sides; transverse median carina with 4 obtuse teeth, 2 inner teeth dorsally with small concavity, distance between inner teeth of dorsal pronotal protuberance as wide as width between eyes; anterior half of pronotum strongly concave, with ocellate punctures, 2 obtuse teeth close to anterior pronotal border, teeth at same level with lateral eye margins when seen from dorsal and lateral views. Prosternal process trapezoidal, concave at the base, posteriorly produced; base with spine-like process posteriorly.

Elytra. Surface smooth, with continuous, slightly convex carinae, weakly impressed interstriae, and with ocellate punctures. Pygidium. Shape convex in lateral view; surface densely punctate; punctures ocellate, moderately sized, elongate near basal margin.

Legs. Protibia with 4 teeth, basal tooth weakly developed. Meta- and mesotibia apically with 3 broaden, shovel-shaped teeth, each tooth additionally furnished with small, apical teeth. The specimen was found dead with damaged abdomen, soft parts and genitalia missing.

Female allotype (Figs 8C, D). Similar to male except by the following features: body length 19 mm, width 8.2 mm; head with cephalic horn less developed, reaching only dorsal pronotal protuberances when seen in lateral view; pronotum longer than high, dorsal longitudinal pronotal concavity about as narrow as width of cephalic horn, uppermost teeth of dorsal pronotal protuberances obtuse, separated by a small fissure.

Derivation of specific epithet.

The species is named after our friend and colleague, Fernando “Fideo” Guerra, for his lifetime commitment to the investigation of the Bolivian fauna. His participation in the actual survey in the southern Bolivian Andes has led to the discovery and description of several previously unknown taxa (e.g., Perger and Guerra 2012), and he was also the first to collect an individual of Oryctophileurus guerrai sp. n.

Geographical and ecological distribution.

Oryctophileurus guerrai is known only from the northwestern area of Tariquía National Reserve (Tarija department) in the southern Bolivian Andes (Fig. 1). The forest in the this area is considered subandine subhumid, semi-deciduous, Tucuman-Bolivian forest (TBF) ( Navarro and Ferreira 2011) with a mean annual temperature of 18.7 °C and an annual rainfall of 1334 mm ( SENAMHI 2007). Oryctophileurus guerrai is likely endemic to TBF (see discussion below) and might also occur in the northern limit (Santa Cruz department) and the Argentinean portion of this forest type (Jujuy, Salta and Tucuman departments).

The two individuals of the new species were collected in a narrow valley (elevation 1008 m a.s.l.) (Fig. 1C). The female was observed during the day on the floor of the densely vegetated, moist gully (Figs 1C, D). The male was found dead in a similar habitat. No individuals of the species were observed in subhumid forest along the slopes and during eight nights of sampling with a light trap close to the collection area. Like the other species of this genus, which are only known from few individuals, Oryctophileurus guerrai might be rare or has a cryptic way of life.

Remarks.

As in males of other dynastine taxa with exaggerated secondary sexual traits(e.g., Eberhard 1979; Rowland 2003),the cephalic horn and pronotal structures of Oryctophileurus armicollis males (and likely in the males of other Oryctophileurus species) vary allometrically. Larger males have larger horns and pronotal armature with respect to their body length. Accordingly, such characters should be compared in specimens having a similar size. Nevertheless, the distance between the inner pronotal protuberance teeth appears to be positively allometric in Oryctophileurus armicollis , since it is wider in larger males (body length 20 mm) than in smaller males (body length 18.5 mm). In the male (body length 20 mm) of Oryctophileurus guerrai the inner pronotal protuberance teeth are separated by a gap (Fig. 6B) that is narrower than in the smaller male of Oryctophileurus armicollis (body length 18.5 mm), indicating that the ratio of body length/ pronotal protuberance teeth distance is never overlapping inter-specifically between similar-sized individuals.

Biogeographical affinities

While the two Amblyodus species occur in Amazon lowland forest ( Amblyodus castroi Grossi & Grossi) and Central American mountain forests ( Amblyodus taurus Westwood) ( Grossi and Grossi 2011), the known distributional pattern suggests that the species of Oryctophileurus are closely associated with forest habitat in the Andean area (Fig. 1).

As proposed for other Andean taxa (see Hoorn et al. 2010 and Rull 2011 for reviews), the diversification of Oryctophileurus might be related to the creation of heterogeneous edaphic mosaics and dispersal barriers by the uplifting of the Andes in the mid-Miocene, marine incursions into the Amazon basin, and the subsequent quaternary climatic cycling. High diversity and endemism in the Andean area are further explained by climatic stability due to orographic rain barriers and lower extinction rates during periods of drastic climatic changes ( Fjeldså et al. 1999). The collection locations of Oryctophileurus species along the eastern slope of the tropical Andes correspond with peak concentrations of endemics (see Swenson et al. 2012; WWF 2012), suggesting that Oryctophileurus species represent biogeographic relicts that persisted during periods of ecological change.

Oryctophileurus in the Southern Bolivian Andes

The discovery of Oryctophileurus guerrai extends the known distributional range of the genus more than 600 km southwards. In view of the mainly tropical Andes distribution of Oryctophileurus species, the presence of this genus in the southern Bolivian Andes, close to the Argentinean border, is surprising. Because of a change in orientation of the mountain ranges at the elbow of the Andes and local topographic features, the TBF is distinguished from Bolivian Yungas forest (BYF) by a more pronounced and prolonged dry season, occasionally accompanied by frost periods ( Fjeldså et al. 1999), and less annual precipitation and humidity ( Ibisch et al. 2003a; Killeen et al. 2007). Corresponding with a general decrease in biodiversity ( Schulenberg and Awbrey 1997; Ibisch et al. 2003b; Churchill and Lozano 2009), several scarabaeoid genera such as Dynastes Kirby, Sphaenognathus Buquet, Scortizus Westwood, and Cantharolethrus Thomson, meet their southern distributional limit at the elbow of the Andes (see Paulsen 2010 for distributional maps).

Nevertheless, the discovery of Oryctophileurus guerrai and other endemic TBF representatives of butterfly genera ( Gareca and Blandin 2011; Blandin and Gareca 2011) and tiger beetle genera ( Perger and Guerra 2012) with diversity center in the northern tropical Andes suggests that the assumed decrease in species richness in some groups is the result of sampling bias and the TBF belongs to the important areas of insect endemism along the eastern slope of the Andes.

This hypothesis should be tested in further studies because human impact and low protection status of such ecoregion (see Schulenberg and Awbrey 1997; Ibisch et al. 2003a) might not only threat already known but also many undiscovered endemics with extinction.