Cryptocephalini

Gómez-Zurita, Jesús & Cardoso, Anabela, 2021, Molecular systematics, higher-rank classification and Gondwanan origins of Cryptocephalinae leaf beetles, Zoologica Scripta 50 (5), pp. 592-615 : 606-607

4.3.5 | Cryptocephalini

With an estimate of 2,800 species, the Cryptocephalini is the largest tribe of Cryptocephalinae and the most diverse, although most species in the tribe (approximately 1,800) belong to a single genus, Cryptocephalus , out of some 45 genera ( Chamorro, 2014a; Schöller, 2002). The size of Cryptocephalini has likely driven taxonomists to split it in more manageable taxonomic units, including several assemblages, fundamentally unaltered for nearly 150 years, which in the current classification correspond to the Achaenopina , Cryptocephalina, Monachulina , Pachybrachina and Stylosomina ( Chamorro, 2014a; Chapuis, 1874; Clavareau, 1913; Seeno & Wilcox, 1982). We already argued that Pachybrachina does not belong to this group and we have no data about Achaenopina ; therefore, the discussion is limited to the other three subtribes. In previous literature, apart from recognizing the existence of these divergent lineages, the relationships among the subtribes were not explored analytically. Authors like Chapuis (1874) or Sharp (1876) effectively treated Stylosomina as sister to the artificial assemblage of Cryptocephalini and Pachybrachini , and Reid (1990) postulated that Stylosomina (and other genera he placed in a “Platycolaspina”) diverged from the assemblage that would group Cryptocephalina and Monachulina . However, our results do not endorse any of these relationships, as several divergent lineages, including the one corresponding to Stylosomina branch off the basal polytomy of the Cryptocephalini clade. Where things get relevant about the classification of Cryptocephalini concerns the two remaining traditional subtribes: Cryptocephalina and Monachulina . Our results dispute the traditional classification, with major changes mostly affecting the subtribe Monachulina , which is strongly rejected by data (AU test, p <<.001). Reid (1998) already mentioned that this subtribe was a polyphyletic group, an artificial assemblage of small cryptocephalines generally characterized by short antennae. His solution to this problem involved splitting the Old World representatives of Monachulina in groups he named “Coenobiina” and “Ditropidina” and transferring the New World Monachulina to Cryptocephalina ( Reid, 1990) . Molecular data endorse these conclusions based on morphological evidence, albeit with a relevant difference. The Cryptocephalini clade in the molecular phylogenies shows a basal polytomy giving rise to five distinct lineages: (a) Stylosomina ; (b) Coenobius and relatives, the “Coenobiina” sensu Reid (1990); (c) Ditropidus and relatives, the “Ditropidina” sensu Reid (1990); (d) Lexiphanes and Diachus (Neotropical Monachulina of the traditional classification) sister to non-Australopapuan Cryptocephalina ; and (e) Australopapuan Cryptocephalina sensu Reid (1990) .

Our samples of Coenobius from the Afrotropical, Oriental and Papuan regions (the latter could be in fact Aprionota ; Reid, 1990) and the Afrotropical Isnus formed a strongly supported clade, and deeply divergent from other Cryptocephalini , deserving the rank of subtribe (the “Coenobiina” predicted by Reid, 1990). This clade is characterized by numerous adult morphological synapomorphies, and it was suggested that African and Australasian lineages could form monophyletic groups ( Reid, 1990). However, the lack of internal support within this clade in our analyses, which covers a vast geographic range, precludes making further taxonomic considerations, beyond questioning, perhaps, the validity of Isnus . Isnus can be distinguished from typical Coenobius by lacking the characteristic large eyes, nearly touching dorsally on frons, but this trait seems to be variable in the lineage and without taxonomic implications, since our sample of Coenobius from Southeast Asia includes other species where eyes are not close together.

Reid's (1990) cladistic analyses of morphological characters separated the group of Australopapuan Monachulina from his "Coenobiina" and, most clearly, from American Monachulina , and he distinguished this assemblage as a subtribe (“Ditropidina”). This group would include the large genus Ditropidus and several allied genera, tentatively treated as synonyms by Reid (1990), as well as the New Caledonian endemic Scaphodius and also, with some doubts, the Southeast Asian genus Adiscus . Our data do not contradict the relationship of Adiscus with the other members of this group (AU test, p =.106), and the results consistently group Australian and Papuan Ditropidus (including species assigned to Bucharis and Elaphodes from Australia) with Scaphodius as an independent lineage, divergent from other Cryptocephalini . However, this clade was resolved with moderate support (BS = 62%) in the ML tree and maximum support (PP = 1.0) in the BI trees as sister to Australopapuan genera currently in Cryptocephalina ( Aporocera , Cadmus and Melatia ). Based on these results, we could advance a hypothesis clustering the two Australopapuan groups in a single new taxonomic (and biogeographic) entity, which could be referred to as the subtribe “Aporocerina” (type genus: Aporocera Saunders, 1842 ). However, its formalization would require a dedicated study of potential synapomorphies for this group as well as a phylogenetic study incorporating more taxa of lineages involved. It is interesting noting here that Australopapuan Cryptocephalina had been already recognized as a natural group divergent from Holarctic, Neotropical and Afrotropical Cryptocephalina as characterized by several synapomorphies ( Baly, 1877; Reid, 1990; Saunders, 1845).

The previous consideration, by exclusion of the Australopapuan genera, would retain Cryptocephalina as the sum of American “ Monachulina ” and American, Palaearctic, Afrotropical and Oriental Cryptocephalina . In this association, the old Monachulina are strongly related to Nearctic and Neotropical Cryptocephalina , a relationship that had been advanced based on the study of immature stages ( LeSage, 1984). This phylogenetic arrangement finds strong support (BS = 93%; PP = 1.0) in our classification and in turn challenges the inclusion of American species in the genus Cryptocephalus . New World and an eastern Palearctic species of Cryptocephalus (C. nr. perelegans from Japan) are embedded in a clade of American lineages, including Diachus and Lexiphanes (former Monachulina ) and Bassareus , and this assemblage is sister (BS = 97%; PP = 1.0) to Old World Cryptocephalus and Melixanthus . The monophyly of Cryptocephalus is rejected statistically (AU test, p <.001) and this generic name should be retained exclusively for Old World species, while the New World lineage of Cryptocephalus could take the name Bassareus Haldeman, 1849 . Cryptocephalus is a huge genus with some 1,800 species according to Schöller (2002), which would drop to less than 1,400 if all the American species were confirmed to belong to a different group. In the restricted interpretation of the genus presented here, it would be distributed in the Afrotropical, Oriental and Palaearctic regions, where it has been subdivided in up to nine subgenera ( Schöller, 2002). Admitting that our sample is very small considering the size of the genus, it actually includes species from the three biogeographic regions, and morphological diversity compatible with several of the subgenera, and even for characters that are supposedly constant in the genus, such as some specimens having appendiculate claws (Vietnamese vouchers 2910 and 2965), when the genus is diagnosed by simple claws. Nonetheless, despite this geographic and taxonomic diversity, which may be indicative of a broad phylogenetic coverage, an interesting, unexpected result from our study was the lack of internal resolution within this group (which also included a sample of Melixanthus ).