Molecular and morphological approaches redefine the limits among polymorphic species in the Neotropical longhorn beetle genus, Myzomorphus Salle (Coleoptera: Cerambycidae: Prioninae)

Myzomorphus Salle is a charismatic genus of prionine longhorn beetles (Cerambycidae) composed of nine species. Myzomorphus species are found from Costa Rica to southern Brazil, but only two species have wide distributions across this range: M. scutellatus Salle from Costa Rica to northern Brazil, and M. quadripunctatus (Gray) from Colombia to southern Brazil. These species are highly polymorphic and their limits are difficult to determine due to their strong morphological similarities--males are only distinguishable by subtle size variations and females by color patterns. Here, we used mitochondrial DNA (cox1 and 12S) to reconstruct the first phylogeny of Myzomorphus and, in combination with morphological data, assess the taxonomic limits between M. scutellatus and M. quadripunctatus. Our phylogenetic results confirm the monophyly of Myzomorphus and reveal a close relationship among M. birai, M. quadripunctatus and M. scutellatus. Using pairwise distance estimations, we found that the intraspecific variation of M. quadripunctatus is remarkably high (K2P: 0-11.7%; p-distances: 0-9.7%) and the interspecific distances of M. quadripunctatus in relation to M. birai and M. scutellatus (K2P: 14.8-20.1%; p-distances: 12-15%) are close to the intraspecific distances of M. quadripunctatus. We further analyzed the diagnostic characters of these species and found that their morphological intraspecific variations largely overlap. Altogether, our results demonstrate that the variability of M. birai, M. scutellatus and M. quadripunctatus represent polymorphisms of a single species. We thus argue for the synonymy of M. birai and M. scutellatus under M. quadripunctatus (syn. nov.) and highlight the need for multiple lines of evidence to solve the taxonomic problems in polymorphic species of Cerambycidae.

Automated summary

Myzomorphus Salle is a genus of prionine longhorn beetles composed of nine species. Two species, M. scutellatus and M. quadripunctatus, have wide distributions across Central to South America and show high polymorphism. By combining molecular and morphological data, the authors reconstructed the phylogeny of Myzomorphus and found that the variability of M. birai, M. scutellatus and M. quadripunctatus represents polymorphisms of a single species. They propose the synonymy of M. birai and M. scutellatus under M. quadripunctatus and emphasize the importance of multiple lines of evidence in taxonomic studies of polymorphic species.