Molecular phylogenetic studies of Lyttini (Coleoptera, Meloidae)

Meloidae is a family of Coleoptera Tenebrionoidea, which includes almost 3000 species in approximately 130 genera well characterized by presence of cantharidin and larval hypermetaboly in the two derived subfamilies. Recent phylogenetic studies, based on both morpho-ethological features and molecular data supported the division of the family in three subfamilies, the basal Eleticinae, the Nemognathinae and Meloinae. The larval dispersion by phoresy is spread in the two apical subfamilies and occurred separately several times in the evolution of the family. Meloinae is the most speciose subfamily and includes 8 tribes. In particular, some genera of the tribe Lyttini have been referred in literature to different tribes, and preliminary molecular evidences did not support the monophyly of this tribe. For this reason we started a molecular analysis focused on all lyttine and some dubious genera. Sequences of two gene markers, namely mtDNA 16S and nDNA CAD, were tested on 62 species belonging to 21 genera previously referred to Lyttini or also to other tribes (Meloini, Epicautini), and five additional species, as outgroups, belonging to three genera of Cerocomini, Epicautini and Pyrotiini tribes. Relationships among most speciose genera such as Lydus, Alosimus and Lytta have been explored by the addition of the nDNA ITS2 gene marker. Aims of this research are: (a) to test the uncertain monophyly of the tribe; (b) to test the inclusion in this tribe of some genera referred to other tribes dubitatively; (c) to define the phylogenetic relationships among genera; (d) to test the monophyly of some speciose genera (such as Lytta), and other greatly differentiated morphologically or divided in subgenera. Analyses was carried out using phylogenetic inference methods (also using 16S secondary structure) on both gene markers, separately and by a combined analysis. All phylogenetic trees show scarce statistic support at basal nodes, while high values support the monophyly of most genera. Some genera, which have been differently placed in the previous literature, such as Berberomeloe, Calydus, Cyaneolytta, Linsleya, Lyttonyx, Physomeloe, Spastonyx, Trichomeloe, belong to Lyttini rather than to other tribes. Australytta and Syriolytta are confirmed as distinct genera. The monophyly of the subtribes Lyttina and Lydina is supported, in opposition with morphological studies based on larval features. Among the subtribe Lyttina, the genus Lydomorphus appears polyphyletic, as suggested by some morphological traits, and surprisingly also Alosimus among Lydina results polyphyletic. Consequently, new genera need to be described and some of them are under study. Relationships among Lytta need more study with the analysis of more species belonging to all subgenera, and Lagorina and Teratolytta could be included in Lytta as subgenera. In the future we will test other nuclear markers (e.g., ITS2 and Wingless) for all taxa, and perform species trees analyses to resolve basal nodes and clarify relationships of some isolated genera.