The puzzling taxonomic rank of Pijnackeria hispanica, a chimerical hybrid androgen (Insecta, Phasmida)

Abstract

The stick-insect genus Pijnackeria includes four diploid bisexual and two polyploid (3n, 4n) parthenogenetic species. Earlier analyses of the tetraploid parthenogen P. hispanica using mitochondrial markers allowed tracing its maternal ancestry to Pijnackeria originis, while no maternal nuclear contribution was found, thus suggesting an androgenetic and hybrid origin. The recently described Pijnackeria recondita—showing, among other features, a specific antennal structure linking it to the tetraploid parthenogen—prompted us to check whether the new species could be the unknown paternal ancestor of P. hispanica. In this work, we use karyology and molecular analysis of the mitochondrial gene cytochrome c oxidase subunit 2 (cox2) and the nuclear gene elongation factor 1 subunit α (ef1-α) to investigate the origin of such a complex tetraploid hybrid parthenogen. The molecular analysis supported P. recondita as being a paternal ancestor of P. hispanica, but also suggested that two more fathering species have to be taken into account: P. barbarae and the unknown paternal ancestor of the triploid hybrid P. masettii. Therefore, P. hispanica is apparently a polyphyletic chimeric androgen, which we propose to indicate as an androgenetic complex. Our data also revealed that P. hispanica is between 1.96 Myr and 3.31 Myr old, making it the oldest parthenogenetic taxon discovered among insects.