New World biogeography and the evolution of polychromatism: evidence from the bee assassin genus Apiomerus (Heteroptera: Reduviidae: Harpactorinae)

The crassipes and pictipes species groups of Apiomerus Hahn together contain 12 species, many with high intraspecific chromatic variability, which represent the majority of Nearctic species in this New World assassin bug genus. Because of their geographical distribution and their varying degrees of polychromatism, these two species groups provide a unique opportunity to study the evolution of polychromatism and analyse relationships among areas of endemism in the Nearctic, as well as determine the boundary between the Nearctic and Neotropical regions. The results of a morphology based phylogenetic analysis allowed investigation of these questions while also determining relationships among the 12 species in the two species groups. The crassipes and pictipes species groups were each supported as monophyletic and as sister taxa. Apiomerus rufipennis (Fallou) was not included in the original concept of the crassipes species group, but is shown here to be a member of the group. Apiomerus barrocoloradoi Forero, Berniker & Szerlip, which had been hypothesized previously to belong to the pictipes species group, is excluded from this group. Intraspecific polychromatism for each species was identified as being present in one of three states: no polychromatism; limited polychromatism; or polychromatism as discrete colour morphs. Limited polychromatism was here found to be the ancestral state for Apiomerus, and species with discrete colour morphs are restricted to the crassipes and pictipes species groups. Polychromatism appears to be a greatly homoplastic character within the genus. A Brooks parsimony analysis recovered distinct Nearctic and Neotropical clades. The Nearctic clade is divided between areas in the central and eastern U.S.A. and areas in the Western U.S.A. and Mexico. The Nearctic–Neotropical boundary for the taxa included in the analysis is along the Isthmus of Tehuantepec in southern Mexico.