Onthophagus clypeatus

Onthophagus clypeatus View in CoL species group.

This group is diagnosed by males having a clypeal horn ( Fig. 5.3 View FIG ); frons of male and female with two horns; male protibia long and slender, with a tuft of long setae at the apex ( Figs. 1.79 View FIG –90); 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 View FIG ); anteriosuperior region of male and female pronotum with two medial keels or humps; pronotum and elytral interstriae smooth with feeble punctures, with metallic luster (evanescent in O. andersoni Howden & Gill and O. grataehelenae Kohlmann & Solís ); pygidium finely punctate.

The present barcode study suggests that the original O. clypeatus species group that Zunino & Halffter (1981, 1997) established comprises three species groups ( O. clypeatus , O. dicranius , and O. nasutus ). Several taxa formerly considered to belong to this group ( Table 3 View TABLE 3 ) now belong to the newly established O. nasutus species group ( Table 4, Figs. 1–2 View FIG View FIG ). This situation would be the second time a species group is derived from the O. clypeatus group, the first one being the separation of the O. dicranius and O. mirabilis species groups by Howden & Gill (1993) from the O. clypeatus species group sensu Zunino & Halffter (1981, 1997).

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Zunino & Halffter (1981) first established the O. mirabilis species complex within the O. clypeatus species group. This first O. mirabilis species complex (sensu Zunino & Halffter 1981) consisted of O. micropterus Zunino & Halffter , O. subcancer Howden , O. mirabilis Bates , and O. neomirabilis Howden. However, Howden & Gill (1993) , Génier & Howden (1999), and Génier (2017) did not include O. micropterus in either their O. mirabilis species group or species complex. Howden & Gill (1987) subsequently divided the O. clypeatus species group into two species complexes, O. belorhinus and O. nasicornis – O. nasutus , and considered them part of the O. praecellens – O. rhinolophus – O. clypeatus species group. Chamé-Vázquez & Sánchez-Hernández (2022) considered that the O. belorhinus species complex to consist of O. andersoni Howden & Gill, 1987 , O. belorhinus Bates , O. grataehelenae Kohlmann & Solís , O. istmenus Moctezuma, Sánchez-Huerta, & Halffter , and O. tacanensis Chamé-Vázquez & Sánchez-Hernández. Subsequently, Howden & Gill (1993) separated an O. dicranius and an O. mirabilis species group from the O. clypeatus species group.

Zunino & Halffter (1997) separated the O. clypeatus species group into three species complexes: O. clypeatus , O. mirabilis , and O. nasicornis . However, Zunino & Halffter (1997) continued to consider the O. dicranius and O. mirabilis species groups of Howden & Gill (1993) as part of the O. clypeatus species group and the O. dicranius species complex as part of the O. clypeatus species complex (sensu Zunino & Halffter 1997). Afterwards, Kohlmann & Solís (2001) merged the O. dicranius and O. mirabilis species complexes into a single O. dicranius species group, separate from the O. clypeatus species group. Génier (2017) redefined the O. dicranius species group and Rossini & Génier (2024), proposed two subgroups within the O. clypeatus species group: O. clypeatus and O. nasutus . The list of species pertaining to the O. clypeatus species group as proposed by Rossini & Génier (2024) matches the one proposed in this study. However, Rossini & Génier (2024) did not provide any definition of what a subgroup is (new terminology) and its hierarchical level relative to previously accepted taxonomic usage in Onthophagus of the hierarchical terms: species group, species line, and species complex ( Zunino & Halffter 1981, 1997; Halffter et al. 2019; see definitions below in O. dicranius species group discussion). Interestingly, the present analysis ( Figs. 1–2 View FIG View FIG ) does not register the existence of any species complexes within the O. clypeatus species group. The bootstrap analysis also recovers the O. clypeatus species group with a bootstrap value of 54 ( Fig. 8 View FIG ).

Palestrini & Zunino (1986) considered in their phyletic analysis that the O. clypeatus species group is the most primitive one of the Western Hemisphere. In their global analysis of the Onthophagus, Breeschoten et al. (2016) suggested a stem origin of the group about 20.5 Mya with a bootstrap value of 99, the oldest for Western Hemispheric Onthophagus , and a recent crown origin of around 3 Mya with a bootstrap value of 100. Moctezuma et al. (2024) considered a stem origin of the group around 24 Mya and a crown origin of around 11.5 Mya. Emlen et al. (2005) and Schwery & O'Meara (2021) also considered the O. clypeatus species group the first to have appeared for the Western Hemispheric Onthophagus . The Costa Rican Caribbean–Pacific vicariance pattern represented by the O. limonensis – O. coriaceoumbrosus and O. nemorivagus – O. propraecellens endemic species pairs ( Figs. 1–2 View FIG View FIG , 8–9 View FIG View FIG ), suggest that species formation must have occurred before the 8–6 Mya period, when Talamanca became a well-defined mountain range, separating the Caribbean and Pacific Southern Central American slopes ( Kohlmann et al. 2024; Solís et al. 2024). This point is discussed below in more detail in the “Biogeography” section. Finally, the greatest intragroup genetic distance range (10.2%) recorded in this study suggests that the O. clypeatus species group is old in origin. The O. clypeatus species group is distributed from Mexico to Bolivia ( Zunino & Halffter 1997).