Defining generic limits in Syndesini MacLeay, 1819 (Coleoptera: Lucanidae: Syndesinae) through taxonomy and geometric morphometrics

A comparative taxonomic study was performed between the Syndesini genera Syndesus MacLeay, 1819 and Psilodon Perty, 1830. Both taxa are redescribed, with the addition of more precise diagnostic traits, including the description of male and female genitalia. We provide comparative remarks to support the separation of both genera, with additional information obtained through the application of geometric morphometric analysis to the following morphological structures: right mandible of males (RMM); lateral view of left mandible of males (LMM); lateral view of males pronotal tubercle (PT); dorsal face of male and female pronotum (DFP); dorsal face of male and female elytra (DFE). The shapes of all analysed traits showed to be different through the performance of Principal Component Analyses producing two well-define clusters, except for the elytral shape which showed a high superposition, however all Procrustes and Mahalanobis distances showed significant differences, supporting the existence of two Syndesini genera instead of one. It was also possible to register a significant influence regarding the biogeographic distribution of the specimens, obtaining statistical differences when comparing the shape data from the Australasian and Neotropical biogeographic dominions, suggesting a strong relation between Syndesus and Psilodon divergence and the Gondwanan vicariant events. Finally, a checklist was provided including all the described species for both genera.