COI-based species delimitation in Indochinese Tetraserica chafers reveal hybridisation despite strong divergence in male copulation organs

Abstract

Species of Tetraserica chafers (Coleoptera: Scarabaeidae: Sericini) can easily be distinguished by the distinct shape of strongly divergent male genitalia; however, it was so far unclear if such divergent copulation organs may avoid hybridisation. Here, we analysed an 826 bp fragment of the mitochondrial cytochrome c oxidase subunit 1 (COI) for a total of 113 Tetraserica individuals out of 38 morphospecies from 33 localities in Southeast Asia. DNA-based species delimitation was performed using statistical parsimony network analysis (TCS), Poisson tree processes (PTP) model, Automatic Barcode Gap Discovery (ABGD) and the generalised mixed Yule-coalescent (GMYC) model. The different approaches for DNA-based species delimitation revealed different numbers of molecular operational taxonomic units (MOTUs) and showed low congruence with a priori assigned morphospecies. GMYC and PTP generally tended to lump morphospecies while ABGD and TCS more often split morphospecies. TCS revealed the highest congruence between MOTUs and morphospecies. While incongruence of species hypotheses was discussed in the context of incomplete lineage sorting and introgression, we could identify two unexpected cases in which introgression occurred between species with highly dissimilar morphology of the male genitalia and that resulted in lumping with DNA-based species delimitation. Most other cases of not matching morphospecies and MOTUs represent young speciation in which standard markers (CO1) do not yet fit the morphological signal of divergence, as reflected by male copulation organs.