Clytrini

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 : 605-606

4.3.4 | Clytrini

Chamorro (2014a) estimatedthatthistribeofCryptocephalinae has some 1,300 species in 62 genera, and they are distributed in all major biogeographic regions, except Oceania. This group and its boundaries have been particularly stable since it was recognized formally, originally separating Old from New World clytrines ( Lacordaire's [1848] Clythrites and Babiites, respectively), but unified in the seminal work of Chapuis (1874), the basis of their classification surviving to this day. The main systematic problems affecting the tribe concern its internal classification, starting from the recognition of subtribes and ending, as will be seen, in the definition of genera. The tribe has been traditionally subdivided into groups that would fit the concept of subtribes in the current system, and depending on the authors, there could be as many as six ( Agrain et al., 2017; Chamorro, 2014a; Moldenke, 1981; Seeno & Wilcox, 1982) or four subtribes ( Clavareau, 1913; Jacoby & Clavareau, 1906; Monrós, 1953; Reid, 1990). A more radical stance was adopted by Bouchard et al. (2011), who discarded Clytrini subtribes altogether. The main difference between these classifications depends on the treatment of monotypic subtribes Arateina, Ischiopachyna and Eoclytrina , which have been variously considered as part of Babiina (the first two) and Clytrina , respectively. In any case, the latest consensus is knowingly rather conservative, despite arguments against splitting these groups, and still defends the six traditional subtribes ( Chamorro, 2014a). Our taxon sampling does not allow testing neither Arateina nor Eoclytrina , but it is illustrative of the other subtribes. First of all, the phylogenetic structure of the data in coherent, strongly supported groups is consistent with the use of subtribes to assist the classification of the Clytrini . Second, these groups match two traditional subtribes, Clytrina and Megalostomina , and a third subtribe consistent with the Babiina of Monrós (1953), that is by placing in the same strongly supported clade Ischiopachys bicolor proteus , representing a putative Ischiopachyna, and five genera of Babiina .

The basis for the current generic system of Clytrini was developed by Lacordaire (1848), who abused the concept of subgenera, particularly for Old World clytrines (i.e. Clytrina ), whereby genera such as Clytra were subdivided in up to 40 subgenera. This massive if tentative splitting was Lacordaire's way to describe the frailty of morphological characters used in this classification. In Lacordaire's own words, this attempt was “une tentative malheureuse pour résoudre un problème que j'ai trouvé insoluble” (p. 13 in Lacordaire, 1848). This system was thoroughly revised by Chapuis (1874) and Jacoby and Clavareau (1906) who proposed several synonymies and made an effort to distinguish smaller groups of subgenera that could be grouped as genera, but did not manage to improve the classification significantly. After these pioneering works, the general approach to the generic classification of Clytrina simply resorted to upgrading the rank of most subgenera of previous authors to genera ( Clavareau, 1913; Seeno & Wilcox, 1982), without a proper character-based, let alone phylogenetic assessment of their validity. Indeed, the generic classification of the tribe, and particularly the subtribe Clytrina , where traditional approaches have struggled to find suitable morphological characters to straighten it up will benefit from a deep phylogenetic study using molecular characters. Despite the low species coverage for most genera in our study, some of them, including Babia , Clytra, Smaragdina and Tituboea , showed strong statistical rejection for their monophyly. Babia is a very diverse and variable genus, split into several subgenera and distributed in the whole of the American continent ( Moldenke, 1981), and our results reflect that some of these subgenera may require a rank upgrade. In turn, the other three genera are among the largest and most widely distributed genera of Clytrina ( Seeno & Wilcox, 1982) , and they have a history of imprecise definition, based on labile characters, starting from the works of Lacordaire (1848), Chapuis (1874) and Jacoby and Clavareau (1906). Clytra and Tituboea may be affected by a similar problem as Babia , with authors unable to recognize that the assemblage of subgenera did not form natural groups. The polyphyly of Smaragdina was certainly expected, since this is a poorly characterized genus, established on plesiomorphic features and putatively related to other similarly ambiguous genera, with species exchanged between these genera depending on authors' preferences ( Warchałowski, 2012). These circumstances already suggest that this is not a natural group and requires a deep analysis to disentangle the objective limits of the genus. In our study, Smaragdina appeared in three deeply divergent groups, one with species allied and remarkably similar to Chilotomina , one with Oriental species and one with the western Palaearctic S. concolor , and each lineage may need referral to a different genus. The debate around Smaragdina also established its close association or even synonymy with Aetheomorpha ( Warchałowski, 2012) , but this is not supported by our results. A final interesting finding worth some commentary because of its implications is the demonstration of a markedly derived position of Anomoea within Clytrina . Anomoea and Smaragdina (possibly requiring reassessment) are the only New World Clytrina and our data are compatible with a recent colonization of the Western Hemisphere from an ancestor in a Palaearctic or Oriental group.