Onthophagus halffteri Zunino, 1981

Sánchez-Huerta, J. L., Tonelli, M., Zunino, M. & Halffter, G., 2015, Redescription of Onthophagus halffteri Zunino (Coleoptera: Scarabaeidae: Scarabaeinae), with Ecological and Distributional Notes, The Coleopterists Bulletin 69 (2), pp. 225-230 : 226-230

Onthophagus halffteri Zunino, 1981 ( Figs. 1–8 )

Redescription. For the hypertelic (major) male

(holotype), we base our redescription on the origi-

nal description by Zunino (1981). Length 14 mm; maximum width close to middle of prothorax. Color black, head and pronotum silky and matte, elytra silky and shiny. Dorsal surface glabrous. Clypeus trnsverse, concave, trapezoidal, apex subsinuate. Gena subparallel; lateral margin of the head angular but not cut at the clypeus-genal limit. Genal sutures evident. Clypeal carina absent, frontal carina relatively strong, not elevated in the middle, straight. Clypeal sculpture thick, transverse, rough, gradually becoming smooth, though remaining thick and slightly transverse toward the front. Lateral margin of prothorax concave between anterior and intermediate angles; basal margin finely margined. Pronotal prominence lengthened and partially covering head in dorsal view, emarginate at apex, lateral tubercules situated in front of intermediate pronotal angles. Sculpture of pronotal disc

6) Hypotelic.

formed by small, undefined, shallow, moderately dense punctures irregular in size, gradually scarcer posteriorly. Posterior margin of pronotum with a median, longitudinal, poorly defined groove. Elytral striae with large, dense, well-defined punctures; microsculpture irregularly gridlike, shallow. Anterior tibiae curved and with internal margin expanded to apes; external margin devoid of microteeth. Terminal spur reduced, medially and ventrally curved. Male genitalia as in Fig. 7 .

Variation. In the new hypertelic material that we examined, the dorsal surface of the body is always shiny black ( Fig. 1 ). The silky matte or silky appearance reported in the original descriptio was likely due to the age of the first specimen described. Size measurements of the hypertelic males range 11.92–14.19 long (n = 27, X = 13.01), as measured from the apex of the clypeus to the apex of the elytra, and 6.40–7.86 mm wide (n = 27, X = 7.20), as measured across the widest part of the pronotum. Eutelic (medium) males ( Fig. 2 ) differ from the hypertelic male in their smaller size (10.96–11.96 mm long, n = 7, X = 11.47; 5.80–6.61 mm wide, n = 7, X = 6.20); the frontal carina is more notable, also in its lateral branches; the pronotal prominence is flattened on its anterior face, missing the triangular protrusion with a notched apex; and the sculpture of the pronotum is somewhat stronger and denser. Hypotelic (minor) males ( Fig. 3 ) are smaller (9.84–10.88 mm long, n = 7, X = 10.37; 4.96–6.28 mm wide, n = 7, X = 5.65); reduced clypeal carina; intact frontal carina, with almost no relief in the center; pronotal prominence almost unapparent; and the pronotal sculpture is stronger and more dense than in the larger males.

Females. Hypertelic (major) ( Fig. 4 ): Size varies 13.01–14.42 mm long (n = 27, X = 13.74) and 6.01–7.64 mm wide (n = 27, X = 7.18). It differs from the male, in addition to the characters of the anterior tibiae common to the whole group, by the transverse, subtrapezoidal aspect of the clypeus; the notable, regularly elevated clypeal carina slightly curved forward and extending between the clypealgenal sutures; the straight, regularly elevated frontal carina with blunt lateral apices and lateral margins practically vertical; and the pronotal prominence only slightly sinuous between the posterior and intermediate angles, with a clearly transverse development at its anterior margin. Eutelic (medium) ( Fig. 5 ): Ranges 11.12–12.95 mm long (n = 9, X = 12.38) and 5.77–6.88 mm wide (n = 9, X = 6.39). It differs from the hypertelic female in the lower degree of development of both cephalic carinae. The pronotal prominence is almost non-apparent, and the pronotal sculpture is somewhat more pronounced. Hypotelic (minor) ( Fig. 6 ): Varies 8.88– 11.32 mm long (n = 6, X = 10.53) and 4.16–5.74 mm wide (n = 6, X = 5.26). Differs mainly in its almost non-apparent clypeal carina, reduced frontal carina, and stronger and denser pronotal sculpture. The minimum values for both length and width were obtained from an exceptionally small female, even for this category. Genitalia as in Fig. 8 .

Given the visual examination of size and degree of expression of secondary sexual traits, the variation in males clearly falls into the three patterns mentioned, while the variation in females is continuous.

Taxonomic Notes. Onthophagus halffteri is distinguished from O. hippopotamus by elytral interstriae with strong, thick sculpturing almost confluent towards the base of the elytra. The striae are strongly arched toward the outside along almost their entire length (less evident in O. hippopotamus and only on the basal third). The interstriae are notably convex starting with the second and with strong punctures more marked toward the base. There are also notable differences in the male genitalia ( Fig. 7 ).

The study of the new material supports previous hypotheses regarding the inclusion of O. halffteri in the hippopotamus line (Zunino and Halffter 1988a and references cited therein). In this context, all of the characters studied suggest that O. halffteri and O. hippopotamus are sister species.

Distribution. MEXICO: Mazatepec, Municipality of Acajete, Veracruz. In the foothills of the Cofre de Perote Volcano, 2,040 m elevation.

Ecological and Distributional Notes. The burrows in which O. halffteri were found were located in Mazatepec (19°34′22.51″N, 097°01′5.67″O, 2,040 m elevation) and Joya Chica (19°35′28.31″N, 097°01′23.64″O, 2,152 m elevation) in the Municipality of Acajete, Veracruz. Both sites are located on the eastern slope of the Cofre de Perote Mountain , at the eastern extreme of the Trans-Mexican Volcanic Belt. They are separated by a linear distance of 2.27 km and a difference in elevation of 158 m. Both are located in a region with a cold temperate climate, where the soil characteristics and the precipitation regime allow for the development of elements typical to mountain cloud forest, upland pastures for cattle, and, to a lesser extent, tree species typical to coniferous forest at higher altitudes .

Onthophagus halffteri is a species that can be considered pholeobic (all stages grow and develop in the nests and burrows of their hosts), strictly associated with gopher burrows ( Rodentia : Geomyidae ). Inside the burrows, it is strongly associated with the nesting chamber and to a lesser degree the latrine chamber. As far as we were able to ascertain, the adults feed exclusively on gopher feces, in addition to using it as a resource for pedotrophic nesting. Onthophagus halffteri builds galleries immediately below the nest or the latrine chamber and packs the rodent feces into these galleries.

Inside the examined burrows, a coprophagous species of Gonaphodioides Dellacasa, Dellacasa, and Gordon ( Scarabaeidae : Aphodiinae) was found in abundance, cohabiting with O. halffteri . This phenomenon of association occurs frequently in systems as specialized as vertebrate burrows and caves (Zunino and Halffter 1988b; Anduaga and Halffter 1991; Lobo and Halffter 1994).

The region where this species was found has been fairly well studied with respect to the coprophagous beetles of the Scarabaeidae ( Arellano 2002; Arellano and Halffter 2003). However, O. halffteri had never been recorded during the systematic sampling conducted previously. We can suppose that its movement between burrows is mostly subterranean, given that flight by individuals to colonize other burrows is not frequent, though like all species belonging to the hippopotamus line, it does not have reduced wings. Onthophagus hippopotamus , on the other hand, has been recorded on the surface, and even collected from beneath other types of excrement such as bovine dung. This latter species, according to Zunino and Halffter (1988a), has a broader geographic distribution than that presently known for O. halffteri . Onthophagus hippopotamus is known from sites located at various elevations along the Trans-Mexican Volcanic Belt ( Fig. 9 modified from Zunino and Halffter 1988a). For at least the eastern face of the Cofre de Perote Mountain, its elevational distribution spans 930 m (2,170 –3,100 m), almost six times greater than that known for O. halffteri . Furthermore, it should be noted that during this study O. hippopotamus beetles were found in the burrows of the gopher Cratogeomys perotensis Merriam , while O. halffteri was captured in association with O. hispidus .

The known distribution area of O. halffteri ( Fig. 9 ) adjoins the eastern end of the area of O. hippopotamus . However, as far as we have determined, there is no sympatry between the two species. It is worth emphasizing that no overlap has been detected for any of the other species belonging to the hippopotamus line that are associated with rodent nests (Zunino and Halffter 1988a). The distribution of these species extends from the mountains of Arizona, the Sierra Madre Occidental mountain range, the Trans-Mexican Volcanic Belt, and the Sierra Madre del Sur mountain range. We assume that a relatively recent event might have separated a peripheral eastern fraction from the ancestor ( hippopotamus + halffteri ). We feel that the separation between the areas of both species could have been precipitated by climate fluctuations related to the glacial-interglacial cycles of the late Quaternary. The fact that the Gonaphodioides sp. associated with O. halffteri differs from those found in association with O. hippopotamus (namely, Geomyphilus pierai Deloya and Lobo and, according to Lobo and Halffter (1994), Neotrichonotulus perotensis Deloya and Lobo ) corroborates our hypothesis.

Figures

Figs. 1–6. Onthophagus halffteri. Males: 1) Hypertelic; 2) Eutelic; 3) Hypotelic. Females: 4) Hypertelic; 5) Eutelic;

Fig. 7. Onthophagus species. Male genitalia aedeagus, lateral view: a) O. halffteri, b) O. hippopotamus. Aedeagus, frontal view: c) O. halffteri, d) O. hippopotamus. Copulatory lamellae: e) O. halffteri, f) O. hippopotamus. Accessory lamellae: g) O. halffteri, h) O. hippopotamus.

Fig. 8. Female genital structures of a) Onthophagus halffteri and b) Onthophagus hippopotamus.

Fig. 9. a) Location of species associated with nests included in the Onthophagus hippopotamus line, taking the new records of Onthophagus halffteri into consideration. Map modified from Zunino and Halffter (1988a). b) Geographic location of O. halffteri and O. hippopotamus on the eastern slope of the Cofre de Perote Mountain. Contour lines are 100 m intervals of elevation.