Phylogeography of the giant harlequin beetle (Acrocinus longimanus)

Aim The extent to which cryptic species contribute to neotropical diversity remains inadequately investigated. Based on its highly distinctive morphology, the giant harlequin beetle, Acrocinus longimanus, is currently described as a single species, ranging from southern Mexico to northern Argentina. However, the discovery of cryptic species in Cordylochernes scorpioides, a pseudoscorpion with obligate dependence on the harlequin beetle for dispersal, strongly suggests the existence of barriers to gene flow in A. longimanus. The aim of this study was therefore to determine whether levels of DNA divergence between geographical populations provided evidence of genetically distinct lineages in the harlequin beetle. Location Trinidad and Panama. Methods Sequencing of 1245 bp of the mitochondrial cytochrome oxidase I (COI) gene of A. longimanus from seven locations in Trinidad and Panama. Results Mitochondrial haplotype diversity in the harlequin beetle shows limited evidence of geographical structuring, with a maximum sequence divergence between populations of only 1.29%. This is an order of magnitude less than the level of COI divergence between harlequin beetle riding pseudoscorpions from the same geographical locations. Main conclusions The molecular data on populations from northern South America and Panama are consistent with the current, morphologically based classification of A. longimanus as a single, pan-neotropical species. In addition, the relatively low level of population divergence detected in this study indicates that speciation in the hitchhiking pseudoscorpion has occurred in the absence of significant barriers to gene flow in its beetle host. It is proposed that, in the harlequin beetle, the phylogenetic signal of colonization and vicariance associated with the formation of the Isthmus of Panama has been obscured, although not fully erased, by historical and contemporary gene flow.