Onthophagus dicranius Bates 1887

Onthophagus dicranius species group. This group is diagnosed by males having a clypeal horn (Fig. 5.2); male protibia long and slender, with a tuft of long setae at apex (Figs. 1.67 –78); metatibial apex with short, thick setae, alternating with thin setae of the same length as the thick setae, or longer, but never more than 2.5 times the size of the thick setae (Fig. 5.5); pronotum and elytral interstriae rough with coarse punctures, without metallic luster; pygidium with large coarse punctures, giving the impression of looking like a honeycomb. The O. dicranius and O. mirabilis species groups were initially established by Howden & Gill (1993). Through a parsimony phylogenetic analysis, they proposed the hypothesis that they both represented sister groups. Subsequently, Génier & Howden (1999) redefined the limits of their O. mirabilis species group through another parsimony phylogenetic analysis. Later, Kohlmann & Solís (2001) considered both species groups to form one, the O. dicranius species group. Finally, Génier (2017) established a conceptual framework for species groups and complexes, thus assigning the status of species complex to the two previous species groups and integrating them into the O. dicranius species group. Génier (2017: 2) defined a species group as having: "a broader scope and encompass species that possess one or more synapomorphies and may have very distinctive external morphologies" and a species complex as: "a group of closely related species that are very similar in appearance to the point that the boundaries between them are often unclear, as seen in the external morphology of the males." Interestingly, Zunino & Halffter (1981) had already defined a species group and a species complex. According to Zunino & Halffter (1981: 100) a species group is: “un raggruppamento omogeneo, con valore filetico, di rango infrasubgenerico. Il termine è quindi equivalente ad Artengruppe dei tassonomi di lingua tedesca”; whereas a species complex is defined as: “Nel caso in cui siano riconoscibile nell'ambito di un gruppo di specie più raggruppamenti di rango inferior, che rappresentano l'esito di altrettante linee evolutive distinte, indichiami tali raggruppamenti come «complessi di specie” (translation: a homogeneous grouping, with phyletic value, of infrasubgeneric rank). The term is therefore equivalent to the “Artengruppe” of German-speaking taxonomists. In contrast, a species complex is defined as: “In the event that they are recognizable in the ambit of a group of species, more groupings of lower rank, which represent the result of as many distinct evolutionary lines, we refer to these groupings as species complexes”. Génier's (2017) usage seems to have won the day over Zunino & Halffter's (1981) usage, possibly because of them having written it in Italian and it not having been repeated and translated into Spanish or English in their subsequent works (Zunino & Halffter 1988, 1997, 2019). The O. dicranius species group is recovered by the present mtDNA barcoding analysis (Figs. 1–2), as well as by the bootstrap analysis (21) (Fig. 8). The O. dicranius and O. clypeatus species groups are considered to be sister groups at a 49-bootstrap value (Fig. 8). Interestingly and according to the barcode (Figs. 1–2), bootstrap (Fig. 8), and partitioned (Fig. 9) analyses, members of what were initially considered species belonging to the O. dicranius species complex (O. dicranius Bates) and the O. mirabilis species complex (O. orphnoides Bates and O. solisi Howden & Gill) coalesce into what can be considered a single O. dicranius species complex at a bootstrap value of 33. This fact would negate the existence of an O. mirabilis species complex, as Kohlmann & Solís (2001) and Génier (2017) proposed. More specimens are needed to resolve this situation. The barcode (Figs. 1–2), bootstrap (Fig. 8), and partitioned (Fig. 9) analyses suggest the existence of a second and new species complex, the O. micropterus species complex at a 73-bootstrap value, comprising four species (O. dorsipilulus Howden & Gill, O. humboldti Kohlmann, Solís & Alvarado, O. micropterus Zunino & Halffter, and O. quetzalis Howden & Gill) (Figs. 1–2). This last species complex originated and diversified in the Costa Rican– Panamanian mountains. The analyses support the removal of O. micropterus from the O. dicranius species complex, as Delgado & Mora-Aguilar (2019) suggested, forming an O. micropterus species complex within the O. dicranius species group. However, Delgado & Mora-Aguilar (2019) did not reassign O. micropterus to any specific grouping. Of note are the results of the barcode analyses. According to the greatest interspecific and intergroup genetic distances in this study, these are concentrated between the O. dicranius and O. chevrolati species groups. This would support, according to previous evidence, that O. dicranius, together with O. clypeatus, its suggested sister group, are the oldest Western Hemispheric species groups, whereas O. chevrolati would represent the most recent species group in the Western Hemisphere. The O. dicranius species group is distributed from Mexico to Ecuador (Génier 2017).