Coptorhina Hope, 1835
Frolov, Andrey V., Akhmetova, Lilia A. & Scholtz, Clarke H., 2008, Revision of the obligate mushroom-feeding African ‘‘ dung beetle’ ’ genus Coptorhina Hope (Coleoptera: Scarabaeidae: Scarabaeinae), Journal of Natural History 42 (21 - 24), pp. 1477-1508: 1479-1485
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|Coptorhina Hope, 1835|
Genus Coptorhina Hope, 1835
Among Scarabaeinae taxa, species of Coptorhina are readily recognized by a combination of two characters: (1) metepisternon somewhat rectangular, widest in its hind part, with secondary suture and very convex epipleural margin ( Figure 1 View Figures 1–8 ); (2) bidentate clypeus ( Figures 2–6 View Figures 1–8 ). Coptorhina shares the first character with the genus Delopleurus Erichson and it is probably a synapomorphy of the two genera. Delopleurus , however, can be easily separated by having a quadridentate clypeus. Males with weakly developed clypeal processes and females of some larger species of Frankenbergerius Balthasar are similar to species of Coptorhina . They can, however, be easily separated from Coptorhina by having a triangular metepisternon which is widest in its anterior part, with slightly convex epipleural margin, and, especially in larger males, by curious clypeal processes ( Frolov and Scholtz 2005).
Beetles are medium-sized (8–20 mm), strongly convex, black or dark brown, glabrous.
Clypeus deeply sinuate in the middle, angulate to dentate at sides of the sinuation. In most species anterior angles of clypeus with short carina directed proximally. Genae rectangular to rounded. Frontoclypeal suture interrupted in the middle, genal suturae distinct. Eyes small, the dorsal part slit-shaped, ventral part sub-rectangular. Distance between eye and gula approximately two times the width of eye in ventral view. Gula with longitudinal groove. Dorsal surface of clypeus rugose in most specimens, frons densely punctate to rugose.
Pronotum more or less trapezoidal, about two times wider than long. Anterior margin and base with feebly distinct, fine border. Lateral margins bordered, width of border varies and is species-specific. Pronotum is excavated in larger specimens of all species except for C. nitidipennis .
Elytra trapezoidal, as wide as long, shiny to opaque, with deep sinuation on lateral margins ( Figure 1 View Figures 1–8 ). Stria fine but distinct, punctate; striae 1–7 reach base of elytron, stria 8 reaches the sinuation but not the base; striae 9–10 are very close to epipleura and mostly inseparable from each other except apically. Elytral intervals flat to feebly convex, sparsely to densely punctate. Elytra fused along sutura. During flight they are closed and slightly elevated. Scutellum not visible from above.
Wings are well developed and feature a number of, probably synapomorphic (Frolov and Scholtz, unpublished), characters that are unique to the genera Coptorhina , Delopleurus , Frankenbergerius and Sarophorus . These are: (1) brown colour of the wing except for very basal part which is almost transparent; (2) reduced anal area (veins J and AP 3+4 are absent); (3) CuA widened apically along the wing margin; (4) RA 4 does not reach the wing margin and becomes wide and indistinct apically ( Figure 9 View Figures 9–14 ) (vein nomenclature follows Kukalova-Peck and Lawrence 1993).
Anterior tibiae have three outer teeth. Margin basad of third tooth more or less serrate. Spur of anterior tibia long, apically acute and curved inwards. Outer margins of middle and posterior tibiae without transverse carinae, serrate. Tarsi of all legs well developed, shorter than tibiae. Claws about half the length of fifth tarsal segment.
Pygidium 2 times wider than long, punctate, bordered, without carinae.
Aedeagus of typical scarabaeinae shape ( Figures 10–11 View Figures 9–14 ). Basal sclerite with two symmetrical tubercles. Parameres symmetrical, without setae, similar in all species. Internal sac with armature; one sclerite (arrowed in Figure 12 View Figures 9–14 ) has a peculiar shape and can be easily homologized among species ( Figures 13A–J View Figures 9–14 ).
Sexual dimorphism is very weak in Coptorhina . Sexes do not differ in the shape of fore tibial spur or clypeal processes, i.e. in characters that can readily separate sexes in genera Delopleurus and Frankenbergerius . It is possible that minor yet statistically significant differences can be found after appropriate morphometric analysis which is beyond the scope of the present revision. The only, albeit ambiguous, character that can separate sexes is a somewhat convex sixth abdominal sternite in males which is more or less flat in females ( Figure 14 View Figures 9–14 ).
In the putatively related genera Sarophorus and Frankenbergerius , which were revised recently ( Frolov and Scholtz 2003, 2005), shape of the parameres and some sclerites of the internal sac of the aedeagus provide a number of diagnostically important characters. Male and female genitalia were studied in a large number of Coptorhina specimens, but, despite some variation (i.e. in internal sac sclerites, Figure 13 View Figures 9–14 ) no reliable diagnostic characters were found in these structures. The only exception is C. nitidipennis which has a somewhat distinctive shape of the internal sac sclerite ( Figures 13I–J View Figures 9–14 ) and parameres ( Figure 11 View Figures 9–14 ). This species can, however, be readily distinguished from other Coptorhina species by the shape of the clypeus which makes dissection unnecessary.
We found that the most reliable characters that can separate Coptorhina species are sculpture of pronotum and elytra and shape of the lateral border of pronotum.
It can be noted that differences among the species of Coptorhina are considerably less distinct than among the species of two other related genera, Sarophorus and Frankenbergerius . In Sarophorus , species differ in a number of structures: male genitalia, body sculpture, appendages. Both paramere shape and internal sac armature are species-specific. In Frankenbergerius , the shape of the parameres is species-specific but in some individuals the character may be ambiguous; armature of internal sac of aedeagus is similar in most species. The species of Frankenbergerius , however, are readily distinguished by the sculpture of upper side of body and by the shape of the clypeal processes in males.
Specimens of Coptorhina vary considerably in size and in shape of the pronotum. For example, in a large series of C. auspicata from Limpopo Province ( South Africa) beetle sizes range from 8.5 mm to 19.5 mm. Specimens also show considerable variation in shape of the pronotum which is strongly excavated anterolaterally in larger specimens and less so in smaller specimens ( Figure 15 View Figures 15–17 ). Small specimens may have the pronotum only slightly excavated with a pair of small tubercles medially.
The highly unusual (for a dung beetle) trophic association between members of the genus and mushrooms was first recorded during the nineteenth century. Coptorhina specimens have been observed feeding on mushrooms with two types of fruit-body. In the case of ‘‘puff-ball’’ mushrooms the adults burrow into the fruit-body, detach pieces and drag them into their burrows. In ‘‘parasol’’ mushrooms, the beetles climb the stalk and detach pieces of the gills, which they then drag into their burrows ( Tribe 1976).
The authors’ observations are limited to South Africa where the beetles occur in highland grassland, savanna and shrubland, in summer rainfall areas. Beetle activity is correlated with the availability of the fruit bodies of mushrooms and is mostly limited to periods after rain. During this study two species ( C. auspicata and C. nitidipennis ) were observed on Cinergy Game Farm (Limpopo Province, South Africa, 24 ° 399S 28 ° 459E) starting from the beginning of the rainfall season (mid-October). For a month, they were common in the area and most of the mushrooms examined were damaged by the beetles. At this time they actively fed and built brood balls for larvae.
Specimens of C. auspicata were collected and bred in the laboratory at the University of Pretoria. The beetles were kept in containers with sandy soil collected in their habitat and were fed on commercial mushrooms ( Agaricus ?bisporus) from a grocery store. The beetles made brood balls about 2 cm in diameter. Typical coprinelike 3 rd -instar larvae were found in the brood balls after three weeks. The larvae were observed to eat the macerated mushroom substance along with sand particles. The smaller size of brood balls (compared to those of dung feeders like Copris or Catharsius with similar sized larvae) is probably due to the higher nutritive value of mushrooms compared to dung. As the larvae progressively consume the brood ball contents and repeatedly re-ingest their own faeces it is likely that bacteria and fungi inhabiting the brood ball substance become the main nutritional component of the larval food.
An apparently unrecorded phenomenon was observed in C. auspicata specimens in which disturbed beetles excreted a whitish substance with strong, unpleasant odour that probably serves to repel predators. The substance is probably a product of the metabolism of the mushroom tissue eaten by the beetles. It is unknown if it is unique to C. auspicata or characteristic for a few species.
Beetles were only observed flying in day time, about half a metre above the ground. None was ever collected at light.
Key to Coptorhina species
1. Clypeal sinuation acute-angled. Clypeal processes without carinae on the
upper sides ( Figure 3 View Figures 1–8 ). Antennal club reddish to dark brown. Elytra
sparsely punctate (punctures separated by 5–6 times their diameters)
........................................... C. nitidipennis
Clypeal sinuation right-angled to rounded. Clypeal processes with
more or less distinct carinae ( Figures 2, 4–6 View Figures 1–8 ). Antennal club dark
brown to black. Elytra relatively densely punctate (punctures
separated by 1–3 times their diameters)....................... 2
3. Disc of pronotum basad of transverse carina with punctures separated by 2–2.5 times their diameters................................. 4 Disc of pronotum basad of transverse carina with larger punctures; sculpture is sometimes rugose........................ C. davidi
4. Carina on pronotum more or less smooth, without tubercles ( Figure 6 View Figures 1–8 ).
5. Lateral border of pronotum about 2 times wider basally than apically. Disc of pronotum more sparsely punctate (punctures separated by 2–4 times their diameters basad of pronotal carina)................... 6 Lateral border of pronotum very wide medially becoming very faint, almost indistinct apically and basaly ( Figure 4 View Figures 1–8 ). Disc of pronotum more densely punctate (punctures separated by 1 times their diameter basad of pronotal carina)..................... C. excavata sp. n.
6. Head with short but distinct fronto-clypeal tubercle ( Figure 2 View Figures 1–8 ). Pronotum densely punctate (punctures separated by 2–2.5 times their diameters). Elytral intervals coarsely punctate, punctures sometimes fused.............................................. C. auspicata Head without fronto-clypeal tubercle. Elytral intervals and disc of pronotum smooth, with small sparse punctures separated by 3–4 times their diameters)................................ C. nitefacta
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