Phylogenetic and morphological discord indicates introgressive hybridisation in two genera of Australian millipedes (Diplopoda, Polydesmida, Paradoxosomatidae)

Abstract

Discord between molecular and morphological datasets was observed in two pairs of species of Australian millipedes in the family Paradoxosomatidae using morphological and molecular phylogenetic analysis (mitochondrial COI rDNA and 16 rRNA, and nuclear 28S rRNA). Close to the presumed distributional boundary between Pogonosternum nigrovirgatum (Carl, 1912) and Pogonosternum jeekeli Decker, 2017, near Dargo in Central Gippsland, Victoria, Pogonosternum specimens were collected which are phylogenetically closer to P. jeekeli in COI and 16S sequences, but are morphologically closer to P. nigrovirgatum. At Mount Osmond, Adelaide, South Australia, eight morphologically typical Somethus castaneus (Attems, 1944) specimens were collected are phylogenetically closer to S. castaneus in 28S genealogy, but three of the eight are closer to S. lancearius Jeekel, 2002 in COI genealogy. These two cases are discussed in terms of hybridisation, past introgressive hybridisation events and aberrant morphology.