Frolov, A.V., Montreuil, O. 2006. Description of the male of the rare Madagascan species Pseudorphnus hiboni with notes on the genus Pseudorphnus (Coleoptera: Scarabaeidae: Orphninae). Zootaxa, 1154: 27-33.

ZooBank: urn:lsid:zoobank.org:pub:21543A3C-1C80-4FA3-80FC-42B75F6EE1B7

Description of the male of the rare Madagascan species Pseudorphnus hiboni with notes on the genus Pseudorphnus (Coleoptera: Scarabaeidae: Orphninae)

A.V. Frolov

Zoological Institute of the Russian Academy of Sciences, Universitetskaya Emb. 1, 199034 Saint Petersburg, Russia; e-mail: afrolov@zin.ru

Abstract

A male of Pseudorphnus hiboni Paulian is described from material recently collected in Ranomafana National Park (eastern Madagascar). The species is compared with the two other known species of the genus. Notes on biology and distribution are given.

Introduction

The scarab beetle (Coleoptera: Scarabaeidae) fauna of Madagascar has a long history of investigation. Many groups of Madagascar scarab beetles, including the Orphninae, were studied by Paulian (1936, 1959, 1977, 1992), but some species are still very rare in collections or known only from type specimens. This is particularly true for many rare genera and species that originate from tropical forest areas of the central and eastern part of the island. These areas are severely threatened by human activities.  Still, almost every collecting trip yields interesting findings of poorly known taxa.

A dung beetles survey in Madagascar was recently started by the Metapopulation Research Group supervised by Ilkka Hanski (University of Helsinki, Finland). Beetles were sampled by pitfall traps in a few tropical wet forests in Madagascar, mostly in Ranomafana National Park. Along with the true dung beetles (subfamily Scarabaeinae), some other scarabs were also collected; chiefly Hybosoridae, Ochodaeidae, and Orphninae. Some of the most interesting findings included one male and five females of the rare species Pseudorphnus hiboni Paulian, 1959. This species was described from a single female (Paulian 1959), and no additional specimens were collected until recently. In the present contribution we describe the male of this species and compare it with the other two species in the genus.

Description

Pseudorphnus hiboni Paulian, 1959: 143

Examined material. Holotype, female: Fort Dauphin, P. Hybon leg., 1943 (Muséum national d'Histoire naturelle, Paris).  One  male: Ranomafana National Park, wet forest, 12.ii.2003, dung trap, Ilkka Hanski leg. (Muséum national d'Histoire naturelle, Paris).  Five females: Vatoharana wet forest, 19.ii.2002, fish bated pitfall trap, I. Hanski leg. (University of Helsinki and Zoological Institute RAS).

Male. Medium-sized beetle (length 11.8 mm, width 7.7 mm) with elongated, oval, strongly shiny body (Fig. 1). Color brown, elytra and underside of body slightly lighter.

 Clypeus slightly convex anteriorly, rounded laterally, anterior margin setose and crenulate in dorsal view. Genae small, not protruding past eyes. Eyes relatively large (diameter larger than the distance between eye and gula in ventral view), incompletely divided by canthus into smaller dorsal and larger ventral parts. Frontal suture absent. Clypeus with relatively long horn rounded apically. Dorsal surface of head impunctate.

Labrum bilobate, slightly sinuate in the middle and relatively feebly protruding past clypeus. Length in the middle is 1/8 width (in dorsal view).

Pronotum 1.5 times wider than long; widest medially. Anterior margin with wide border, base with fine border. Lateral margins densely punctate, appearing crenulate in dorsal view. Disc of pronotum with deep, somewhat transverse excavation in the middle, with two horns bordering excavation near anterior margin. Pronotal horns as long as clypeal horn but more slender, directed upward and forward (Fig. 2). Surface of disc between the horns smooth, without punctures. Sides of pronotum rugose, somewhat tuberculate posteriorly. Lateral margins with long, brown setae.

Scutellum triangular, narrowly rounded apically, about 1/10 length of elytra.

Elytra convex, with feebly marked humeral umbones. Maximum width approximately at the middle. Elytra with 7 distinct striae on disc. Striae with characteristic, narrow, semicircular punctures. Each puncture with a short, yellow seta. Only sutural stria reaches elytral apex. Striae 2-5 about 2/3 length of elytron, striae 6-7 about 1/3-1/4 length of elytron and do not reach elytral base. Epipleura with long, sparse, brown setae. Base of elytra bordered and densely punctate with punctures similar to those in striae and forming a tile pattern (Fig. 9).

Wings fully developed.

Anterior tibiae of typical shape of Pseudorphnus, with 2 strong outer teeth and a small one located basally. Lateral margin basad of outer teeth not crenulated. Apices with 3 robust, spur-like setae and a number of smaller ones. Anterior tarsi well developed, about 4/5 length of protibiae. Claws 1/3 length of apical tarsal segment. Apical segment of anterior tarsus as long as segments 3 and 4 combined, as thick as other segments. Ventral surface of anterior tibiae smooth with two rows of setae along sides and sparse longer setae in the middle. Ventral surface of femora sparsely punctate, with 1 raised longitudinal line. 

Figures 1–7. Pseudorphnus. P. hiboni (1–4, 7), P. olsoufieffi (5), P. coquereli (6).
Figures 1–7. Pseudorphnus. P. hiboni (1–4, 7), P. olsoufieffi (5), P. coquereli (6). 1, 4—habitus; 2—lateral view of head and thorax; 3—aedeagus in dorsal and lateral view; 5–7—parameres in lateral view.

 

Middle and posterior legs similar in shape; posterior femora and tibiae about 1/8 longer than middle ones. Tibiae somewhat triangular, with two apical spurs, with inner margin only slightly concave and with 1 transverse keel. Longer tibial spur as long as two basal segments of tarsus. Claws 1/3 length of last tarsal segment. Femora almost impunctate, with two rows of long setae.

Abdominal sternites irregularly punctate, pubescent with dense, long setae. Sternite 6 medially as long as sternites 4-5 combined.

Pygidium transverse, irregularly punctate, hidden under elytra.

Aedeagus (Fig. 3, 7) with slender, finger-shaped apices, feebly tapering apically.

Sexual dimorphism. In addition to the common character of sexual dimorphism of the Orphninae (absence of the protibial spur in males), the male of P. hiboni also differs from the female in having the pronotum deeply excavated in the middle and with two horns on either side of the excavation. The pronotum of the female is only slightly impressed anteriorly with sparse punctures in the middle, as opposed to being smooth in male (Fig. 4). The clypeus of the female lacks any traces of tubercles. The female holotype has a distinct row of punctures immediately next to the elytral suture (probably first sutural stria), whereas the male lacks a distinct row and has only a few punctures. This character is probably subject to interspecific variation rather than being sex dependent. The sixth abdominal sternite is as long as sternites 3-5 combined in female, whereas in the male it is as long as 4-5 sternites combined. The pronotum is 10% wider in male. The sexes are similar in general body shape and color.

Variation.  The length of the females from the Vatoharana forest varies from 11.0- 12.8 mm, width from 6.1-7.9 mm. Specimens have a few narrow, semicircular punctures along the suture but not a distinct row of punctures as in the holotype. Otherwise the specimens are similar to the holotype.

Differential diagnosis. Pseudorphnus hiboni differs from the other species of the genus, P. coquereli (Fairmaire) and P. olsoufieffi Paulian, in its larger body size. The length of the examined specimens is 11.0–12.8 mm, whereas that of P. coquereli is 6.5–8.5 mm and of P. olsoufieffi is9.5–10.5 mm. It also differs in having relatively slender horns either side of the excavation near anterior margin of pronotum in male. Protibial horns are directed upward and forward; horns of the other species are located in the middle, wider and keel-shaped. Base of elytra of P. coquereli (Fig. 8) and P. olsoufieffi is with the similar (crescent-shaped punctures, less developed in the former species), but punctures do not form a tile pattern. The species of Pseudorphnus also differ in the shape of parameres, which are wider apically in P. olsoufieffi,hook-shaped in P. coquereli, and finger-shaped in P. hiboni. The clypeal horn is somewhat rounded in P. hiboni as opposed to being depressed and wider in P. coquereli (the only known male specimen of P. olsoufieffi has a short, tubercle-like, rounded horn).

Habitat and biology.  The Ranomafana National Park is situated about 100 kilometers west of the Indian Ocean on the east-facing escarpment of Madagascar's central high plateau and covers about 43 000 ha of tropical wet forest with elevations varying from 400-374 m. The climate is subtropical, with annual mean precipitation of 2600 mm and temperature of 21°C. Yearly rainfall varies between 2300-4000 mm (Overdorff 1993). During the survey in the Park, biology of the Pseudorphnus or other Orphninae species was not specifically studied, but some data can be inferred from the collecting methods. The trapping was done in the Talatakely secondary forest area and Vatoharana primary forest area. Beetles were sampled with standard pitfall traps baited with fish and chicken intestine. Traps were set up 10-20 m apart along trails in Talatakely and Vatoharana, or in groups of two or seven along transects from the forest edge towards the inner forest. Trapping time in each case was approximately 45 hours including two nights (Heidi Viljanen, personal communication). Only traps in the Vatoharana primary forest captured specimens of P. hiboni. Short-time exposures of the traps suggest that the beetles were attracted to the carrion rather than accidental captures. 

Figures 8–10. Pseudorphnus. 8–9—SEM micrograph of basal part of elytron (8— P. olsoufieffi, 9— P. hiboni); 10—distribution map of species (■—P. hiboni, ▲—P. olsoufieffi, ●—P. coquereli
Figures 8–10. Pseudorphnus. 8–9—SEM micrograph of basal part of elytron (8— P. olsoufieffi, 9— P. hiboni); 10—distribution map of species (■—P. hiboni, ▲—P. olsoufieffi, ●—P. coquereli; larger symbols indicate type localities).

 

Discussion

Analysis of the distribution patterns of the three known species of the genus Pseudorphnus suggests that the species are allopatric and distributed chiefly along the eastern slopes of the escarpment corresponding to the distribution of the Malagasy tropical wet forests. Representatives of the genus show regular changes in the size from north to south on the island: the smallest species (P. coquereli) occurs in the north, the largest one (P. hiboni) in the south, and the intermediate one (P. olsoufieffi) in the center (Fig. 10). Pseudorphnus olsoufieffi also has somewhat intermediate characters of the sculpture of pronotum and elytra which could suggest a hybrid origin of the examined specimens. The shape of the parameres, however, is quite distinct from that of the two other species. Therefore, we consider P. olsoufieffi a valid species. Extensive sampling, especially in the central part of the island, should be undertaken to determine the natural ranges of the species in order to form a hypothesis for the mechanisms of speciation in the genus Pseudorphnus.

Key to Pseudorphnus species  

1 Elytra without distinct striae, punctuate on disc; elytral intervals almost flat; parameres with acute apices (in lateral view, Fig. 5) ... P. olsoufieffi

- Elytra with distinct striae, punctuate or impunctate on disc; elytral intervals convex or flat; parameres of different shape ... 2

2 Elytra with densely punctuate striae (Fig. 1, 4); elytral intervals somewhat convex; protibial horns of male directed upward and forward; apices of parameres finger-shaped (Fig. 3, 7); larger (11-13 mm)  ... P. hiboni

- Elytra almost impunctate on disc, with striae visible as slightly elevated lines; elytral intervals almost flat; protibial horns of male wider and directed upward; apices of parameres hook-shaped (in lateral view, Fig. 6); smaller (6.5–8.5 mm)  ... P. coquereli

Acknowledgements

We thank Heidi Viljanen (University of Helsinki) for the opportunity to examine the specimens of P. hiboni and for the information about the survey in the Ranomafana National Park. Marc De Meyer and the directorate of the Royal Museum for Central Africa (Tervuren) are gratefully acknowledged for providing facilities for this work. Comments from Andrew Smith (Canadian Museum of Nature) and two anonymous reviewers considerably improved the manuscript. This work was supported by a postdoctoral fellowship from the Belgian Office for Scientific, Technical and Cultural Affairs to Andrey Frolov.

Literature cited

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