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Global Studies of the Host-Parasite Relationships between Ectoparasitic Mites of the Family Syringophilidae and Birds of the Order Columbiformes

Simple Summary Mites of the family Syringophilidae (Acariformes: Cheyletoidea)—also called quill mites—are permanent and highly specialized ectoparasites of birds living inside the calamus of the various types of the feathers. In the present paper, we conducted a study focused on prevalence, host specificity, networks, and phylogeny of the syringophilid mites parasitizing on pigeon and doves (Columbiformes). We postulate that the Syringophilidae mites and Columbiformes bird system represent a model which can be used in a broader study of the relationship between hosts and parasites. Abstract The quill mites belonging to the family Syringophilidae (Acari: Prostigmata: Cheyletoidea) are obligate ectoparasites of birds. They inhabit different types of the quills, where they spend their whole life cycle. In this paper, we conducted a global study of syringophilid mites associated with columbiform birds. We examined 772 pigeon and dove individuals belonging to 112 species (35% world fauna) from all zoogeographical regions (except Madagascan) where Columbiformes occur. We measured the prevalence (IP) and the confidence interval (CI) for all infested host species. IP ranges between 4.2 and 66.7 (CI 0.2–100). We applied a bipartite analysis to determine host–parasite interaction, network indices, and host specificity on species and whole network levels. The Syringophilidae–Columbiformes network was composed of 25 mite species and 65 host species. The bipartite network was characterized by a high network level specialization H2′ = 0.93, high nestedness N = 0.908, connectance C = 0.90, and high modularity Q = 0.83, with 20 modules. Moreover, we reconstructed the phylogeny of the quill mites associated with columbiform birds on the generic level. Analysis shows two distinct clades: Meitingsunes + Psittaciphilus, and Peristerophila + Terratosyringophilus.


Introduction
Knowing how many species inhabit Earth is among the most fundamental questions in science [1]. Despite often being neglected [2], one of the major components of biodiversity are parasites [3], comprising at least half of all species [4][5][6]; up to 75% of all interactions in food webs involve a parasitic species [3]. Many estimates of global species diversity of parasites are based on extrapolations of patterns of host specificity [2]; however, a contrast between the proportion that parasites comprise in local and global faunas suggests that parasites are most probably less host specific and more widespread than local scale studies suggest [6]. To get over such difficulties, it has been increasingly recognized that biotic (ZSM) and Museum of Natural History, Nairobi, Kenya (NMK). These bird collections have been previously used as donors of mite species described or recorded in the several published papers (see Skoracki and Dabert [40]; Skoracki and Glowska [37]; Glowska and Skoracki [39], Skoracki [22]; Skoracki and Hromada [41]; Skoracki et al. [47]; Kaszewska and Skoracki [42]; Kaszewska et al. [42][43][44][45][46]). We also analyzed the host specimens collected from frozen collections housed in several veterinary centers. Bird specimen was examined using a dissecting microscope and the infested quills were opened with a fine scalpel. From each bird specimen, we removed one wing covert, about 5 under-tail coverts, and about 10 contour feathers. Before mounting, mites were softened and cleared in Nesbitt's solution at room temperature for three days [22], and then mites were mounted on slides in Hoyer's medium.

Bipartite Networks and Statistics
The bipartite graph consists of rectangles representing compartment species and the width is proportion to the sum of interaction involving this species. Interacting species are linked by lines whose width is proportional to the number of interactions [51]. To visualize patterns in the studied host-parasite-ecological web, we used the 'bipartite' package available for R software [51]. To visualize bipartite networks we used functions plotweb ( Figure 1) and visweb ( Figure S1). For all host species recorded in earlier papers without information about prevalence, we gave score 1. Indices were calculated by using networklevel and network-species functions available in bipartite packages.
We calculated the following bipartite index: network specialization (H2 ) nestedness (N), connectance (C), and modularity (Q), to measured interaction on species-level we used species specialization metrics (d'). For this purpose, we prepared the matrices where quill mites species are in the rows (parasites) and the bird species (host) in the columns. 'H2' network-level measure of specialization, based on the deviation of a species' realized number of interactions and that expected from each species' total number of interactions [52]. Values of H2' range from 0 to 1, where 0 indicates low specialization, while 1 suggests high specialization [53]. We also calculated the connectance, defined as the proportion of possible links observed in the network [54], ranged from 0 (low connectance in the network) to 1 to imply more connectance in the network. Nestedness measures how many interactions realized by specialists are a subset of those realized by generalists. The base metric of nestedness is the nestedness temperature T (0 • -100 • ), which measures the departure from a perfectly nested interaction matrix [55]. For this study, we used a binary system, where metrics define as N = (100 − T)/100, with values ranging from 0 to 1 (maximum nestedness) [56][57][58].To calculate network modularity we calculate 'likelihood' implemented in computeModules in the bipartite library for R; this index is the same value as Q (or M), the modularity as given by Newman [59] or Guimerà & Amaral [60] and well known from QuanBiMo (Q) library [61], currently not supported. According to network permutation, we obtained 100 Q values (observed likelihood) [62] and compared them with 100 Q values coming from permutations for null models (null likelihood). To test a significant difference between the Q observed and Qnull values, we calculated the null.t.test (p < 0.05). For each quill mites species associated with doves and pigeons in the network, we calculated d' index measured specialization at species level [52].

Prevalence
Descriptive statistics were computed using Quantitative Parasitology on the Web [63], with 95% confidence intervals (Sterne method).

Mite Phylogeny
In the cladistic analysis, we examined relationships at the generic level. All operational taxonomic units (OTUs) were represented by taxonomic species, i.e., type species for each genus. A free-living predator Cheyletus eruditus (Schrank) and quill-inhabiting predator Metacheletoides numidae Fain both belonging to the sister family Cheyletidae, were used as outgroups in the analyses. Because each particular syringophilid genus is represented by a single species in the present analysis, the character states appearing as autapomorphies represent true synapomorphies for genera.
A total of five OTUs representing all genera associated with columbiform birds, two taxa as the outgroup, and 26 non-additive and unordered morphological characters were included in our data matrix (data matrix and morphological characters are supple-mented ( Figures S2 and S3)). A detailed discussion of the morphological characters used in the present study is provided by Skoracki [22]; Skoracki et al. [47]. The matrix was done using NEXUS Data Editor 0.5.0 [64]. Analyses of character distribution on the tree were performed in WINCLADA [65]. Only unordered, qualitative, and unweighted characters were used in analyses. We applied a multistate contingent coding strategy [66], which is considered as the most useful among available approaches [67]. Following this strategy, characters with multiple states were interpreted as unordered and not modified into binary characters. Reconstruction of phylogenetic relationships was performed with PAUP 4.0 beta version for IBM [68] in conjunction with PRAP2 [69] to conduct a ratchet analysis (1000 iterations; 10 random cycles, collapsed zero-branches in effect; options are the default). Nodal support was evaluated by Bremer indices calculated with PRAP2. Analysis of character distributions, drawing, and editing of the trees was performed in TreeView 1.5.2. [70].

Visualization of Host Phylogeny
To visualize host phylogeny, a tree of the columbiform species was constructed based on a consensus avian phylogenetic tool available at http://birdtree.org/ (accessed on 5 March 2019) [71]. As the source of our consensus tree, we used the 'Hackett All Species tree' with 1000 randomly generated trees. The most credible tree was then determined using the tool TreeAnnotatorv1.8.2 in the software BEAST v1.8.2 [72]. The consensus tree was then graphically adjusted in FigTree v1.4.2 (Andrew Rambaut, University of Edinburgh, UK; http://tree.bio.ed.ac.uk/software/figtree/ (accessed on 5 March 2019)).

Host Specificity
Host specificity for particular mite species follows Caira et al. [73] and Skoracki et al. [47]. The division stands out monoxenous species (parasite infest single host species), oligoxenous (more than one host, but restricted to one genus), mesostenoxenous (more than one genus of hosts, but restricted to one subfamily), metastenoxenous (more than one subfamily of hosts but restricted to one order), and polyxenous species (more than one order). The common and scientific names of the birds follow Clements et al. [10]. Zoogeographic regions follow Holt et al. [74].

Results
A total of 772 individuals of pigeons and doves and belonging to 29 genera and 112 species were examined for the presence of quill mites belonging to the family Syringophilidae. Among them, 117 individuals representing 65 species had been infested by the quill mites belonging to the following genera Meitingsunes  (Tables 1 and S1).
In total, 22 out of 25 known quill mites species associated with Columbiformes birds were identified (Terratosyringophilus geotrygonus, T. longisoma, and M. adwelles were not found). Among non-infested columbid specimens, some taxa were examined for the presence of quill mites for the first time, for example: Reinwardtoena reinwardtsi, Gymnophaps albertisii, Henicophaps albifrons, and Henicophaps foersteri.

Prevalence Index Birds from Order Columbiformes
The index of prevalence (IP) of host species from Columbiformes order ranges from 4.2% to 100% (IP = 100 in 17 cases); however, the confidence intervals were wide and ranged from 0.2 to 100 ( Table 2). In our material, 49 host species (239 individuals) were not infested by the syringophilid mites.

Host Specificity of the Quill Mites
Based on previously recorded host species, we classified all syringophilids associated with columbiform birds into the following host specificity groups (Tables 3 and 4

Co-Infestation of the Quill Mites
The analysis of the host spectrum showed several various patterns of co-infestation with niche factor (quill mites occupying a different habitats) ( Table 5): (1) "Syr-Pic" (quill mite species belonging to the differential subfamily Syringophilinae or Picobiinae and inhabiting the same host species but different habitats.
We also measured specialization on the species-level (d'). Quill mites specialization ranged between 0.20 and 1 (see Tables 3 and 4). The strength (thickness of connecting bar between parasites and hosts) of each interaction is representative of the number of interactions (prevalence). Each link corresponds to species interaction and represent quill mites genera: red-Gunabopicobia, blue-Meitingsunes, black-Terratosyringophilus, green-Psittaciphilus, yellow-Peristerophila. Host phylogeny based on Jetz et al. [68].
We registered a high modularity (likelihood = 0.83) with 20 modules. Modules were split to (A) single-host (quill mites associated with one host species), (B) multi-host (quill mites associated with more the one host species), and (C) multi-parasites (modules encompasses more than one quill mite species) modules (Figure 2).

Zoogeographical Distribution of Quill Mite Species Associated with Pigeons and Doves
Based on previous reports (see Table 1), we summarized the distribution of the Syringophilidae associated with birds from order Columbiformes. Quill mite species were recorded in hosts inhabiting the following zoogeographical regions: Neotropical, Nearctic, Panamanian, Palaearctic, Saharo-Arabian, Afrotropical, Oriental, Australasian, and Oceanian (Table 6, Figure 3). In particular regions, we noted the following genera with number of quill mites species:    Among all quill mites species, eight of them were only noted from one region: Neotropical-Gunabopicobia metriopelia, G. claravis, G. leptotila, Meitingsunes adwelles, Psittaciphilus patagioenas Terratosyringophilus geotrygonus; Afrotropical-Meitingsunes tympanistria; Australian-Peristerophila leucomela. Others quill mites species were recorded from more than one zoogeographical region:

Phylogenetic Analysis
The analysis under equal weights resulted in one most parsimonious tree (MPT) shown in  The analysis shows that except the genus Gunabopicobia which represents subfamily Picobiinae, other syringophilinae genera form two distinct clades: Peristerophila + Terratosyringophilus (supported by synapomorphies: the presence of large finger-like protuberances on the hypostomal apex, presence of parallel apodemes I, and presence of dimorphic females) and Meitingsunes + Psittaciphilus (supported by synapomorphy: the presence of the constricted posterior end of the stylophore.

Discussion
The parasitological studies on quill mites of the family Syringophilidae and their hosts have a long history spanning over 140 years [16,22]. However, the extensive studies on this group of parasites started about 40 years ago, and investigation of a small fraction of the about 10,000 extant bird species recognized to date recording of more than 400 species of syringophilid mites arranged in 63 genera and two families [20].
The studies on the host-parasite relationship in the system composed of quill mites and the particular taxonomical groups of their hosts are still rare in the literature. Moreover, comprehensive research of the quill mite fauna on the host representatives of the whole bird order and considering mite species richness, host and habitat specificities, prevalence, and phylogenetic relationships have not been provided so far. Most of the previously published papers have focused on describing syringophilid fauna of the particular zoogeographical regions e.g., [22,23,77], or on taxonomical reviewing the different taxa (genus or subfamily) of quill mites e.g., [23,26,41,78]. Recently, however, there have been published a few studies examining the syringophilid fauna on the particular taxonomical host groups (e.g., passeriform genus Estrilda [25], sub-Saharan Nectariniidae [24], cuckoos [79]), with primary analyses of host-parasite relationships.
This paper focuses on analyses of the species richness and measuring specialization and interaction between syringophilid mites parasitizing columbiform birds in their natural host-parasite system.

Species Richness and Phylogenetic Relationship of Quill Mites Associated with Columbiform Birds
The fauna of quill mites associated with doves and pigeons encompasses 25 species belonging to the following five genera: Meitingsunes, Peristerophila, Psittaciphilus, Terratosyringophilus (subfamily Syringophilinae), and Gunabopicobia (subfamily Picobiinae) (see Table 1). Among them, only one-Gunabopicobia-is exclusively associated with columbiform birds and represented by monoxenous (3 species), oligoxenous (1), and mesostenoxenous (3) parasites. Thus, this genus is a perfect example of the host-parasite interaction where a supraspecific taxon of parasites is associated with one host order. This genus is known from hosts representing all columbiform subfamilies, i.e., Claravinae, Columbinae, and Raphinae. It was suggested by Kaszewska et al. [26] that mites of this genus could have started to parasitize the common ancestor in the Late Cretaceous (about 41 to 46 MYA) before their split on the particular subfamilies. Moreover, the Columbiformes are one of the oldest lineages of extant birds. A recent molecular study based on the complete mitochondrial genome suggests that the earliest radiation of the Columbidae occurred during the late Oligocene and continued diversification of the major clade in the Miocene [15]. However, older data suggest that the Columbiformes radiated from Eocene to Oligocene [13,14] or even from Early Eocene to middle Miocene [12].
Four genera of the syringophilines associated with columbiform birds have been previously assigned to the Psittaciphilus-generic-group [80]. In this study, we identified phylogenetically closely related clades Meitingsunes + Psittaciphilus and Peristerophila + Terratosyringophilus.
The genus Meitingsunes comprises nine described species where eight of them are exclusively associated with pigeons and doves infesting birds belonging to two subfamilies Columbinae and Raphinae (28 infested species in total) [45]. However, only one species of this genus, M. caprimulgus, has been noted from the phylogenetically distant clade of nightjars (Caprimulgiformes) [50]. Because birds belonging to the order Caprimulgiformes are extremely poorly examined (with only one host record), the status of Meitingsunes on nightjars is still unclear. The nightjars can represent real hosts for quill mites of this genus, or the single findings of M. caprimulgus can be an example of host-switching (e.g., from the columbiform host).
The genus Psittaciphilus includes four species found on representatives of Columbiformes (2 species) and Psittaciformes (2) [33,42]. On pigeons and doves, this genus infests birds of the genera Geotrygon and Patagioenas, which are also parasitized by members of the genus Meitingsunes mentioned above (e.g., M. zenadourae and M. adwelles).
The genus Terratosyringophilus includes three quill mites species found on parrots and two species noted from doves belonging to the subfamily Columbinae [31,34,35,37,81].
The Terratosyringophilus quill mites along with Psittaciphilus and partially Peristerophila (see below) have been found in birds from orders Columbiformes and Psittaciformes. The cases where both host orders are infested by mites belonging to the same genera can indicate the phylogenetically close relationship between these two bird orders. However, recent phylogenetic analysis does not confirm this hypothesis. It is commonly accepted that the lineage of doves and pigeons is a sister clade to sandgrouse (Pteroclidiformes) and mesites (Mesitornithiformes) [15,[82][83][84]. At this moment, we cannot explain this multi-order infestation of the same genera of syringophilid mites. To resolve this problem, the molecular analyses of the quill mites phylogeny are needed as well as the studies on the host spectrum of the other symbionts parasitizing birds of these both orders.
Considering high-level examination of columbiform birds under the presence of the quill mites, we suppose that the Syringophilidae fauna on the generic level has been fully explored. In the future, it would be worth intensifying research on the syringophilids inhabiting a single bird order. It will allow comparing our results with these ones conducted for other host orders. This approach allows for a better understanding of the parasite-host relationship as a whole. It would also be interesting to provide comprehensive studies on quill mite fauna associated with pacific island doves and pigeons. The future collection of the material from these regions will allow testing MacArthur and Wilson's "the island theory" for quill mites. Additionally, future molecular studies on co-phylogeny also give important information about the relationships and evolutionary events between particular columbid and quill mite species.

Prevalence
The prevalence index provided details of the strength of the relationship between a particular host and parasites species. Our study has shown that the prevalence of infested birds by the quill mites ranges between 4.2% and 66.7%. However, for 17 hosts species, IP was equal to 100%, the confidence interval (CI) was wide, and this result can be the effect of the small sample size of studied host specimens.
Both factors, the number of examined bird individuals and the number of examined feathers, play a crucial role in determining the real prevalence of infested hosts in the environment. In current and previous studies on prevalence, the used bird material was from various sources. The first source includes birds deposited in the museum collections (mostly dry bird skins and frozen or alcohol preserved specimens) e.g., [24,25]. The second source are birds examined during fieldworks (e.g, [18,48,88,90,92,93,95,[98][99][100][101]) or kept in the zoological gardens [97] and farms [94,96,102].
It is obvious that syringophilid mites infest not all host specimens in nature and not all feathers, and to present the real IP, we should examine as many as possible bird individuals (taking into consideration their age, season, locality, etc.) and as many as possible feathers; see also [93,95,103]. However, samples collected from ornithological collections and from live birds are limited and allow sampling only a few feathers. Therefore, to minimize this limiting factor, we should continue studies on habitat specificity (see below).

Habitat Specificity and Multi-Infestation of Syringophilid Mites
The feather environment gives opportunities to inhabit various niches by ectoparasites and commensal species. However, the phenomenon of co-infestation remains poorly documented, especially for ectoparasites belonging to the family Syringophilidae. The first remark about multi-infestation was pointed out by Kethley [16]. He indicated that one host species or even one host individual may be infected by several syringophilid species inhabiting different types of feathers. Later on, Schmäschke et al. [104] presented the observation of co-infestation of two species, Syringophilopsis turdi and Syringophiloidus sp. on one the fieldfare Turdus pilaris (Passeriformes: Turdidae), and Syringophilopsis kirgizorum and Syringophiloidus sp. found on the greenfinch Carduelis chloris (Passeriformes: Fringillidae). Other examples of multi-infestations were described by Skoracki et al. [91]. In this paper, the authors recorded the following patterns of infestation with the notation of infested niches, e.g., Torotrogla rubeculi (habitat: secondaries) + Picobia sp. (habitat: contour feathers) on the European robin Erithacus rubecula (Muscicapidae); Syringophilipsis kirgizorum (primaries) + Torotrogla gaudi (secondaries) on the chaffinch Fringilla coelebs (Fringillidae); Syringophiloidus presentlis (secondaries) + Picobia sturni and Aulonastus buczekae (habitat: contour feathers) on the common starling Sturnus vulgaris (Sturnidae).
Until now, the multi-infestations by quill mites have been observed only in passeriform birds. However, our study described other cases of syringophilid multi-infestation on columbiform birds and showed that the phenomenon of co-infestation can occur more frequently. In total, we found 13 examples of co-infestation in different configurations. The most frequent cases of co-infestation were recorded for quill mites that inhabited the same host species but occupied differential niche-"factor niche". For these cases, we observed two co-infestation patterns: (1) "Syr-Pic pattern"-quill mites belonging to two subfamilies Syringophilinae and Picobiinae occupying the same host individual or species; and (2) "Syr-Syr pattern"-quill mites belonging to the same subfamily, Syringophilinae. Currently, the pattern "Pic-Pic", i.e., two species of picobiine mites on the same host species, was not observed. In members of the "Syr-Pic pattern", representing two subfamilies, differences in morphology, life strategies, and niche preferences are clearly visible. For example, Picobiinae inhabit exclusively contour feathers while the members of Syringophilinae occur mainly inside the quills of secondaries, wing or tail coverts, rectrices; however, they are also occasionally found in contour feathers (Tables 2 and 5). For the "Syr-Syr pattern", we observed a similar strategy of avoiding competition by occupying different feathers.
However, for this group, we found two species, Peristerophila columbae and Psittaciphilus patagioenas, that infested the same host species and occupied the same niche-quills of wing coverts. Probably, this event could be an example of the horizontal transfer.
Niche separation among quill mites is a result of avoiding competition for the same microhabitat. According to the niche conception, the differential species cannot occupy the same niche (and use the same resources) because the advantage for one competitor will eventually drive others to extinction [105][106][107]. Finally, niche separation is the process of natural selection which drives competing species into using different hosts or different microhabitats [108].
Examples of niche separation are common and well documented for other ectoparasitic mites, e.g., mites from genus Schizocarpus infested Castor fiber [109] or feathers mites such as Microspalax brevipes and Zachvatkinia ovata associated with Calonectris borealis [110]. However, knowledge about competition and niche overlap phenomena for ectoparasites of the Syringophilidae is still unsuccessfully documented. The following examples of coinfestation in syringophilid groups provided in our study confirm the previous reports on the high degree of specificity of the quill mites to occupying niche. The observed preferences of syringophilids to colonize various types of feathers can result from the preferences to the specific parameters of the quills, such as the thickness of the quill wall and its volume. This hypothesis was proposed by Kethley [17], Casto [18], and Glowska et al. [111]. Moreover, recent studies by Grossi and Proctor [93] confirmed a strong correlation between quill volume and the average number of quill mites.

Bipartite Network of the Quill Mites-Doves Communities
The ecological network approach provides a lot of information about biological systems. Networks can be useful to illustrate and analyze the relationships and ecological interactions inside various types of communities [8]. Recently, an extensive study of an ecological network aimed to describe the character of mutualistic plant-animal interactions (pollination, seed dispersal, etc.) [5,56,112,113]. However, the network-thinking approach may also be useful in the study of the parasite ecology. Those analyses give a visual graph that illustrates links between two trophic levels, but above all, quantify indices such as host specificity in parasites and provide the topological description [5,9].
In the present study, to describe the bipartite network, we used the following indices: connectance (C), nestedness (N), modularity (Q), and H2'. The values of these metrics provided information about: the number of interactions, the level of sharing partners, the degree of compartmentalization of the networks, and network-level specialization [52,115,116]. Our results confirm the hypothesis about the high specialization of syringophilid mites associated with pigeons and doves. We found strong specialization on both the network-and the species-level. The architecture of the quill mites-doves network was characterized by a high: connectance (C = 90), nestedness (N = 0.908), H2' (H2' = 0.93), and also with simultaneously high value of modularity (Q = 0.83) with 20 modules.
Recent studies of ecological networks have shown that the metrics such as nestedness, modularity, and connectance are correlated and depend on one another [57,58,117], which can be useful to understand the interaction between particular species in the network. One of the most important indices used to describe the quill mites-doves network was nestedness. We noted a high value of (N) = 0.908, close to 1. According to Bascompte et al. [56], the results close to 1 indicate a non-random community structure with a high level of diversity and complexity. Moreover, quill mites-doves communities were shown to have a highly modular structure. Modularity measures the tendency of a network to divide into modules (also called groups, clusters, or communities) [57]. It promotes stability by containing perturbations within a module, thereby constraining their spreading to the rest of the community [118]. In our networks, we found 20 modules, each of them had a strong interaction between species inside the modules. Some recognized modules ( Figure 2) have more than one quill mite species, e.g., module number "3" had the highest number of quill mites species: G. geotrygoni, M. zenadourae, P. montanus, and M. columbicus. These multi-parasite communities interact with numerous hosts and probably can result from the phylogenetic relationship between particular quill mites and their hosts. The genera Psittaciphilus and Meitingsunes are sister clades (Figure 3) within subfamily Syringophilinae and share the same close relation to host species, while the genus Gunabopicobia is a separately evolutionary line. Moreover, those results suggest the structure of communities where competition for hosts can be expected. We observed another situation for modules where only one quill mite species has infested one host species. Those communities are represented, for example, by Gunabopicobia metriopelia associated with one host species, Metriopelia melanoptera. In this case, strong interaction with hosts species was observed.
The next indicator of complexity-connectance-was used in this study. The strong link between parasitic species and individual hosts (C = 0.90) observed in our research may be the result of non-random infestation.
The similar architecture of the bipartite network was presented in a study of ectoparasitic flies of the family Streblidae (Hippoboscoidea) and bat hosts from the tropical dry forest [113]. The authors of this study obtained structures similar to ours, such as high specialization (H2' = 0.67), high modularity (Q = 0.7), but, contrary to the quill mites-doves nest, the authors found a low value of connectance (C = 0.30). The differential between C index can be related to sampled and network size. This relation was observed in the following networks: food webs (marine, estuarine, terrestrial), plant-pollinator, plantherbivores-parasitoids in the forest [119][120][121]. However, some authors suggest that the connectance decreases when specialists are lost or generalists are gained [122,123]. In the quill mites-doves network, the proportion of specialized species is higher compared with the bat-fly network. Additionally, some analyses focusing on the conservation and protection of biodiversity suggest that the high C-value characterizes more stable communities, while low C-value can be an indicator of an ecological threat [122]. We hypothesize that the high C-value is observed in the stable and old hosts-parasites systems.
The Columbiformes and syringophilid mites have a long, common history. Quill mites have probably been associated with birds hosts for a very long time. Some studies based on the phylogeny of Syringophilidae and birds indicate that the quill mites of the family Syringophilidae could be associated with Neornithes birds around 66 million years ago or earlier [124]. Currently, the family Syringophilidae comprises about 400 species associated with birds from 27 orders. Most infested bird species belong to the clade Neoaves. However, quill mites species have also been found in Paleognathae (2 quill mite species), as well as Galloanserae (23 quill mite species) [20]. Considering the richness of parasites that inhabit modern birds, [124] suggested that their origins are not later than the Late Jurassic. Phylogeny analysis conducted by Skoracki et al. [78] showed that the mites on the earliest derivate branches are associated with birds of the advanced clade Neoaves. In contrast, genera associated with the earliest clades of extant birds, such as Tinamiformes (Palaeognathae) and Galloanserae (Anseriformes and Galliformes), are mosaically distributed in the core of the tree. On the other hand, ancestors of the quill mites could be associated with bird-like creatures before the K-Pg extinction event. Phylogeny analysis of parasitic mites from the superfamily Cheyletoidea (Acariformes: Prostigmata) showed that the Syringophilidae probably originated from a common ancestor with Cheyletidae, a predatory ancestor and inhabiting the litter of bird nests [124,125].
However, comparing the presented results with another host-parasites network is still unsatisfactory. The network-thinking approach used for the study of ectoparasites-hosts systems is limited. The most available research on bipartite networks was conducted on the mutualistic plant-pollinator food web. Moreover, we suggest that co-evolutionary analysis will be important to understand better the nature of the relationship between quill mites and doves.

Conclusions
The relation and interactions between host and parasites are still not well understood. We believe that this study focused on host specificity, prevalence, networks and evolutionary aspect has a particular role to identify the relation between host and parasites. The results of the presented study show that the quill mites belonging to family Syringophlidae and associated with pigeons and doves (Columbiformes) form stable and non-random communities.
The quill mites-doves bipartite has been characterized by a high value of nestedness, connectance, modularity, and H2'. We suggest that the observed network architecture in this study as well as high specificity and worldwide distribution of syringophlid mites is characteristic for: high host specificity systems with a long and common history.