Comparative Phylogenetic Study on Host Newts (Caudata: Salamandridae) and Parasitic Mites (Acariformes: Hydrachnidia: Hygrobatidae) in East and Southeast Asia

The water mite genus <i>Hygrobates</i> and the newt family Salamandridae are distributed widely in the northern hemisphere. However, only in Eastern and Southeastern Asia a host-parasite association developed, with several <i>Hygrobates</i> species, which belong to the subgenus <i>Lurchibates</i>, parasitizing newts of the genera <i>Laotriton</i>, <i>Pachytriton</i>, and <i>Paramesotriton</i>. Presently, there is no molecular study on parasitic <i>Hygrobates</i>, which impedes our understanding of their phylogeny and the evolutionary history of the host-parasite association between <i>Lurchibates</i> and their hosts. In this study, we performed comparative phylogenetic analyses on parasitic <i>Lurchibates</i> mites and their newt hosts based on their respective phylogenies. Our results did not support the monophyly of parasitic species of <i>Hygrobates</i>, but instead, group them significantly with a free-living species, <i>H. longiporus</i>. Among the parasitic species, <i>H. forcipifer</i>, <i>H. macrochela</i>, <i>H. malosimilis</i>, and <i>H. robustipalpis</i> are significantly grouped together, while branching patterns of the remaining species were not supported. Distance-based approaches of cophylogeny analysis between hosts and parasites found no significant link. On the other hand, among all the cost schemes constructed by event-based cophylogeny methods, four cospeciation events, two duplication and host-switching events, one loss event, and two failure to diverge events between parasitic water mites and newts were discovered. Our findings suggested that host switching events might have played an important role in the evolution of these parasitic mites, which might have led to incompletely exclusive host-parasitic relationships at species level.