A comprehensive survey of Rhinonyssid mites (Mesostigmata: Rhinonyssidae) in Northwest Russia: New mite-host associations and prevalence data

Abstract Background Rhinonyssid mites are permanent parasites of birds that inhabit their respiratory tract. There are around 600 species described worldwide and almost all species of birds are found to have embedded rhinonyssid mites. Despite their presumed relevance, these mites are largely unstudied due to the difficulty in sampling them and, therefore, the majority of mite-host associations and species-prevalence data are unknown. New information In this study, 179 mite specimens belonging to 27 species and eight genera were identified. Notably, 18 new mite-bird associations were documented for the first time, thus increasing the known host range for these mite species. In addition, mite-host associations found in this study were compared with known associations from these species of birds in the European part of Russia and in Europe. Overall, this study represents the largest survey to date carried out on rhinonyssid mites in Russia and one of the most comprehensive datasets on rhinonyssid host-range.


Introduction
Nasal mites of the family Rhinonyssidae are permanent haematophagous endoparasites of birds that inhabit their respiratory tract (Vitzthum 1935;George 1961;Fain 1994;Dimov and de Rojas 2012). Most species live in the nasal cavity on the vascularised epithelial tissue; nevertheless, some species occupy the lungs, tracheal tissues and body cavity of their hosts (Lindquist et al. 2009;). Rhinonyssids can not only cause damage to their hosts in a direct way (Rhinonyssidosis avium disease) (Dimov 2011), but could also be reservoirs or vectors of other infections like West Nile fever, Q fever, avian influenza and Lyme disease, as have been shown in mites from the family Dermanyssidae (Reeves et al. 2006). Despite their ecological relevance, most aspects of the basic biology, ecology and evolution of these mites are still poorly understood. This lack of knowledge, amongst other reasons, is owing to their being very challenging to study; for example, due to most species having typically low prevalence on their hosts and being difficult to sample (being only possible to collect from dead birds).
The family Rhinonyssidae currently includes about 600 described species arranged in eleven genera (Domrow 1969;Fain 1994;Dimov et al. 2015;Dimov 2018). In Parasitology, parasite host-specificity and prevalence are widely-studied parameters as they are informative of relevant processes, such as parasite degree of specialisation, population dynamics or transmission efficiency (Poulin 2011). Host specificity of rhinonyssid mites has been found to vary from one genus to another by surveys across different geographic areas (e.g. USA, Spicer 1987;Canada, Knee et al. 2008). In particular, some genera have been found to be constrained to a single host family, while others can inhabit hosts from different orders (Pence 1975;Butenko 1984). In addition, these studies have found that the prevalence of these mites varies across geographic areas (although the estimates may be biased by a low sample size; Spicer 1987). However, the host-specificity and prevalence of most rhinonyssid mites are still poorly understood, thus hampering further studies on the ecology and evolution of this host-parasite system.
In this study, 2,107 bird specimens from northwest of Russia, belonging to 75 species from 55 genera, 30 families and 10 orders were examined for rhinonyssid mites. The mites were identified and the prevalence (including confidence intervals to show how accurate the estimates are) of these species was calculated. Additionally, the mite-host associations, found in our study, were compared with the known rhinonyssids from these species of birds Quality control: The nasal cavity of birds was opened following Butenko's method (Butenko 1984), with some changes introduced by us. In particular, 1) the nasal cavity was opened with a scalpel and scissors under a binocular stereomicroscope. 2) The ossa mandibulae were removed along with the hyoid brush apparatus (apparatus hyobranchialis); the eyeballs were removed with tweezers. 3) Then, two incisions were made: a transverse incision in the region of the papillae pharyngeales and a medial incision, from the rima infundibuli (through the choana) to the ruga palatina mediana area. 4) Nostrils in the area of operculum were examined and then the os maxillare were opened. 5) Lastly, the maxillary bone was removed and the nasal cavity with three conchs was opened, including the largest of all rostral -concha nasalis rostralis, the middleconcha nasalis media and the caudal -concha nasalis caudalis. The examination of all nasal cavities was performed with tweezers and a dissecting needle under a binocular stereomicroscope. Rhinonyssid mites were placed in tubes with 70% ethanol for storage. Each tube was labelled with data on the type of host and a detailed description of the collection site. Mites were then cleared in lactic acid and mounted on slides with Fora-Berlese liquid, according to the generally-accepted technique for small mites ). Finally, individual mites were identified, based on morphometrics analysis.

Taxonomic coverage
Description: A total of 2,107 individual birds were collected, representing 75 species belonging to 55 genera, 30 families and 10 orders. The majority of the studied hosts (59 species from 36 genera) belonged to the order Passeriformes (the most numerous and widely-distributed order of birds of the northwest of Russia) (Table 1). Specifically, sampled passerine species comprise up to 58% out of the total number of species of passerine species inhabiting the territory of the northwest of Russia (Malchevsky and Pukinsky 1983). In general, 179 mite specimens belonging to 27 species and 8 genera were identified. From a total of 27 host-mite associations, we report 18 novel host-mite associations ( Table  2). As expected, due to the higher sampling effort in Passerifoms, the number of new hostmite associations was the highest in this order (9 out of 18), followed by waterbirds belonging to Charadriiformes and Anseriformes (with 4 and 3 new host-mite associations, respectively). Only a single new host-mite association was detected in Caprimulgiformes and Cuculiformes. Lastly, no new association was found in Columbiformes, Galliformes or Piciformes.

Number of data sets: 1
Data set name: Table S2 Description: Host-mite associations form a total of 2,107 individual hosts totalling 75 bird species from 30 avian families and 10 orders (Suppl. material 3). Information on eight mite genera and 28 mite species from Rhinonyssidae is presented. Each row depicts an individual bird from mite-host associations, in which more than one mite was found. See Table 2 for more information (e.g. prevalence).

Column label Column description
Bird taxa Scientific name and authority of bird taxa

Discussion
In the present study, the rhinonyssid mite species collected from 2,107 bird individuals from 75 bird species at 41 sites in Northwest Russia were reported. A total of 27 host-mite associations were found, from which 18 were novel ( Table 2).
The prevalence of rhinonyssid mites was found to vary between bird taxa, as found by previous studies (Spicer 1987; Table 1). Interestingly, the prevalence values found here were lower overall (particularly low in Passeriformes) than those found by previous studies (e.g. 4.41%, this study vs. 17%, USA, Spicer 1987; or 15-16%, Canada, Knee 2018). The lower values found here may be due to differences in climatic conditions, as have been found by previous studies (e.g. Spicer 1987). Overall, our results support current expectations that rhinonyssid mites are generally associated with low prevalence with their hosts (Spicer 1987;Knee 2018).
The mite-host associations found in this study were compared with those known from the same host species inhabiting the European part of Russia and Europe (see Suppl. material 2). In particular, a higher number of mite species of rhinonyssid genera was found in the northwest of Russia compared to the European part of Russia and Western Europe (Suppl. material 2). This pattern was particularly noticeable for species-rich genera, such as Sternostoma, Mesonyssus, Rhinonyssus and Ptilonyssus. In addition, the pattern was most acute between the northwest of Russia and western Europe. For instance, there were almost no common species between these two areas (only 14 common species from six genera). In contrast, almost all genera (five out of eight) of Rhinonyssidae were shared.
On the other hand, some species that have been found in the European part of Russia and Europe were not found in this study (e.g. Mesonyssus hirsutus from Columba livia; Ptilonyssus nudus from Fringilla coelebs; Ptilonyssus pari from Parus ater; Parus caeruleus or Parus europea; Rhinonyssus vanellus from Vanellus vanellus). Overall, these differences in diversity could be the outcome of the lack of knowledge about these mites in these regions. Indeed, differences in sampling effort (i.e. some groups have been more extensively sampled in Northwest Russia than in other geographic areas) may be biasing these interpretations. Overall, further studies aimed at ascertaining whether specific rhinonyssid mite species are found throughout all their host distribution are encouraged. In this vein, global syntheses are needed to draw more general conclusions on the distribution of rhinonyssid mites. Additionally, future studies describing new species are required to catalogue the unknown diversity of this group of mites. In addition, new molecular approaches (e.g. DNA metabarcoding of complex samples; Doña et al. 2019) would help to accelerate the discovery of new species along with validating the species status of previously-described rhinonyssid species, as cryptic species are known in this group (de Rojas et al. 2018).