Two New Species of Pristionchus (Nematoda: Diplogastridae) from Taiwan and the Definition of the pacificus Species-Complex Sensu Stricto

Sommer, Carta, Kim, and Sternberg, 1996 is an important model organism in evolutionary biology that aims to integrate developmental biology and evo-devo with population genetics and ecology. Functional studies in are supported by a well-established phylogenetic framework of around 30 species of the genus that have been described in the last decade based on their entomophilic and necromenic association with scarab beetles. Biogeographically, East Asia has emerged as a hotspot of speciation and recent samplings have therefore focused on Islands and mainland settings in East Asia. Here, we describe in a series of three publications the results of our sampling efforts in Taiwan, Japan, and Hongkong in 2016 and 2017. We describe a total of nine new species that cover different phylogenetic species-complexes of the genus. In this first publication, we describe two new species, sp. n. and sp. n. that are closely related to . Together with five previously described species they form the “ species-complex sensu stricto” that is characterized by all species forming viable, but sterile F1 hybrids indicating reproductive isolation. sp. n. and sp. n. have a gonochorist mode of reproduction and they are described using morphology, morphometrics, mating experiments, and genome-wide sequence analysis. We discuss the extreme diversification in the species-complex sensu stricto in East Asia and its potential power to study speciation processes.