Onthophagus chevrolati, Harold, 1869

Halffter, Gonzalo, Zunino, Mario, Moctezuma, Victor & Sánchez-Huerta, José L., 2019, The integration processes of the distributional patterns in the Mexican Transition Zone: Phyletic, paleogeographic and ecological factors of a case study, Zootaxa 4586 (1), pp. 1-34 : 28-29

The Onthophagus chevrolati species line

In contrast to Zunino & Halffter (1988a), we think that O. cyanellus and closely related species deserve to be considered a species line that is distinct from the O. chevrolati species line (see “Taxonomy of Onthophagus chevrolati species group, updated from Zunino & Halffter (1988a) ” and “The hipotetically oldest stages of evolution of the Onthophagus chevrolati species group”). This leaves the line O. chevrolati as the most recently difersified set of species within the O. chevrolati species group. Its geographic distribution is also the most modern (end of the Pliocene to the Anthropocene; Figs. 16–20 , 22 ). As we have proposed (“Introduction” and “The Onthophagus hippopotamus species line and species complex”), the spatial distribution of the O. hippopotamus species line and the formation of the mountain systems of the TMVB are simultaneous phenomena. The dispersal and speciation of the O. chevrolati species line occurred when this mountain landscape already had its current configuration. Apart from its association with high mountains, the O. chevrolati species line does not have any special ecological characteristics. The morphology of its species is very uniform. These species probably originated during a recent radiation process, and only differ by very small characters. Taken together, we think that O. chevrolati is a much more modern species line than the O. hippopotamus species line.

The O. chevrolati species line is composed of several complexes that follow the Paleoamerican Mountain distributional sub-pattern, with distributions that correspond to different biogeographic times and settings, ranging from the Pleistocene to the Anthropocene. Thus, the O. aureofuscus species complex (for the taxonomic composition of this line and its complexes see “Taxonomy of Onthophagus chevrolati species group, updated from Zunino & Halffter (1988a) ”) expands in the Sierra Madre mountain systems ( Fig. 19 ). The O. chevrolati and O. fuscus species complexes have a u-shaped distribution in the cordilleras that surround the Mexican High Plateau, with a notable presence in the Oaxacan mountainous areas ( Figs. 16 , 17 ). To the west, the species of the O. chevrolati species complex that reaches the furthest north (Arizona) is O. cochisus Brown.

In the TMVB, the O. chevrolati species complex predominates. Several species have an aggressive distribution, certainly recent. Arriaga-Jiménez et al. (2018), studying the coprophagous beetles (Aphodinae, Geotrupinae , Scarabaeinae ) of four mountains at the eastern end of the TMVB and that is in contact with the Sierra Madre Oriental, suggest that only “ O. chevrolati chevrolati Harold ” was found on all the mountains. Nevertheless, they mistakenly considered O. chevrolati , O. retusus Harold and O. orizabensis as the same species. As a matter of fact, both O. chevrolati and O. retusus are found in all the high mountains of the eastern TMVB. The general distribution of O. chevrolati includes the TMVB and the Sierra Madre Oriental, the mountainous areas of the southern Mexican High Plateau, while O. retusus occurs in the eastern TMVB, the southern Sierra Madre Oriental, and the sierras of Puebla-Oaxaca, both species with a broad elevation distribution from 1800 to more than 3000 m a.s.l ( O. retusus occurs near the sea level in its southernmost distribution area). In the Sierra Madre Oriental, 900 km to the northeast is the northernmost species of the species complex, O. coahuilae Zunino & Halffter.

In the TMVB, the O. fuscus species complex is represented by several species, and has two species in the Sierra Madre Oriental. The O. undulans species complex is located in the Sierra Madre del Sur, with an expansion into the Puebla-Oaxaca Mountain System. In the western and central parts of the TMVB, but not in its eastern part or in the Sierra Madre Oriental, there is the O. aztecus species complex, at elevations around 2200 m a.s.l. It is clear that the different species complexes of the O. chevrolati species line occupy different mountain systems in the central part of the MTZ. It can be inferred that their dispersal occurred when the mountain systems already had their current conformation (end of the Pliocene to the Pleistocene).

Figures

FIGURE 16. Distribution of the O. chevrolati species complex.

FIGURE 17. Distribution of the O. fuscus species complex.

FIGURE 18. Distribution of the O. undulans species complex.

FIGURE 19. Distribution of the O. aureofuscus species complex.

FIGURE 20. Distribution of the O. aztecus species complex.

FIGURE 22. Comparison of the distribution areas of the O. hippopotamus and O. chevrolati species lines.