Infestation dynamics of Hygrobates (sg. Lurchibates) aloisii (Acari: Hygrobatidae) and host-parasite interactions with Hong Kong newts (Paramesotriton hongkongensis)

Various species of water mites (Hydrachnidia, Hygrobatidae, <i>Hygrobates</i>) exclusively parasitise Asian modern newts. These water mites, grouped into the subgenus <i>Lurchibates</i>, are evolutionarily unique as they are the only ectoparasitic water mites of amphibians. However, the ecology of this subgenus has been under-investigated. Therefore, we aim to study the newt-mite associations by focusing on the mite <i>Hygrobates aloisii</i> and its host Hong Kong newt (<i>Paramesotriton hongkongensis</i>). We investigated the spatial and temporal patterns of the mite infestation throughout the host's breeding season. The effect of parasitism on the host body condition is also examined at both the population and individual levels. We sampled three infested and three non-infested newt populations in the year 2022-2023, with four of the sites also sampled in the subsequent two years. Three standardised surveys were conducted at each site in each breeding season. High prevalence was found within and across the breeding season. The temporal pattern of infestation intensity differed between adult and deutonymph (one of the developmental stages) mites at the end of the breeding season, with adult mites showing a plateau of high intensity, whereas deutonymph intensity decreased. Additionally, no evidence of negative effects of mite parasitism was found on host body condition, despite reports of mite-related skin lesions on <i>P. hongkongensis</i> and previously on a congeneric newt. Finally, we found deutonymph mites attaching to the body surface of developmental and adult newts, representing two new host-parasite interactions in the newt-mite association. Overall, our findings contribute to a new understanding of the newt-mite association and highlight the importance of considering infestation dynamics in future studies of this association.