Parasite-host relationships of water mites (Acari: Hydrachnidia) and black flies (Diptera: Simuliidae) in southeastern Spain

BACKGROUND

Documentation on water mites in Spain is scarce, as is information on the parasite-host relationship between certain water mite species and representatives of the dipteran family Simuliidae. The discomfort caused to humans and animals by black flies seems to be increasing in recent years. In this context, an investigation of parasitic water mites is of great importance, not only from the point of view of biodiversity, but also in terms of their potential to control black fly populations.

METHODS

Rivers across a wide region of eastern Spain were sampled to determine the specific richness of simuliid dipterans and to investigate their possible parasites, such as water mites, mermithid nematodes and microsporidia (fungal microbes). Data on environmental variables, abundance, prevalence and intensity of parasitism on the collected specimens were analyzed.

RESULTS

In 10 streams, 15,396 simuliid pupae were collected and checked for the presence of water mite larvae; 426 pupae in seven streams were found to be associated with water mite larvae. Of the 21 simuliid species identified based on morphological characters, eight were found to be associated with water mite larvae. Water mite infection was not equally distributed among black fly species. Also, the prevalence of parasitism was low and differed among simuliid species, ranging from one to 13 water mites per black fly pupa. Variation at the intra- and interspecific levels was detected in terms of the number of water mites inside the black fly cocoons. Free-living deutonymphal and adult water mites representing 15 different species of six genera and five families were morphologically identified. The taxonomic identity of the parasitic mite larvae is unclear at present. Morphologically, they fit descriptions of larval Sperchon (Hispidosperchon) algeriensis Lundblad, 1942, but the possibility cannot be excluded that they represent Sperchon algeriensis, the most abundant species at the adult stage in this study and unknown at the larval stage, or even another species of the genus. A molecular analysis produced for the first time cytochrome oxidase I gene sequences for S. algeriensis.

CONCLUSIONS

Our results contribute to current knowledge on Spanish Hydrachnidia and their relationships with simuliids as hosts. However, further research is needed to evaluate the diversity, distribution, bioecology and prevalence of this parasitism.

"Hitchhicking with invertebrates": two reports of epibiosis by peritrich ciliates on ostracods and hydrachnid mites in tanks of epiphytic bromeliads from south Brazil

Temporary waters are common environments found in physical and biological substrates. Among them, some bromeliads species are known to hold water in their tanks, in a habitat called phytotelmata. Phytotelmata serve as habitats for several organisms, from bacteria and protists to arthropods and anurans. Peritrich ciliates are often found as epibionts on aquatic invertebrates in these environments. Here, we report two cases of epibiosis involving Lagenophrys sp. attached to ostracods (Elpidium spp.) and Rhabdostyla sp. colonizing hydrachnid mites in the tanks of two bromeliad species. In our analysis, we measured the frequency of epibiosis considering the presence of both basibiont and epibiont in the samples. The results shown a significant difference between Elpidium sp. and Lagenophrys sp. compared to hydrachnid mites and Rhabdostyla sp. (87.5% and 19%, respectively), supported by the Kruskal-Walis test (p = 0.0003, Chi-square = 9.687). These reports are important since the knowledge of phytotelmata communities from tropical and subtropical areas is incipient, although it has been increasing over the last years. It also shows that epibiosis doesn't always represent a beneficial relationship. These two epibiosis systems found in bromeliad tanks raise questions about organism's dispersal throughout other phytotelmata and other temporary water habitats.

Improved Chironomid Barcode Database Enhances Identification of Water Mite Dietary Content

Chironomids are one of the most biodiverse and abundant members of freshwater ecosystems. They are a food source for many organisms, including fish and water mites. The accurate identification of chironomids is essential for many applications in ecological research, including determining which chironomid species are present in the diets of diverse predators. Larval and adult chironomids from diverse habitats, including lakes, rivers, inland gardens, coastal vegetation, and nearshore habitats of the Great Lakes, were collected from 2012 to 2019. After morphological identification of chironomids, DNA was extracted and cytochrome oxidase I (COI) barcodes were PCR amplified and sequenced. Here we describe an analysis of biodiverse adult and larval chironomids in the Great Lakes region of North America based on new collections to improve chironomid identification by curating a chironomid DNA barcode database, thereby expanding the diversity and taxonomic specificity of DNA reference libraries for the Chironomidae family. In addition to reporting many novel chironomid DNA barcodes, we demonstrate here the use of this chironomid COI barcode database to improve the identification of DNA barcodes of prey in the liquefied diets of water mites. The species identifications of the COI barcodes of chironomids ingested by Lebertia davidcooki and L. quinquemaculosa are more diverse for L. davidcooki and include Parachironomus abortivus, Cryptochironomus ponderosus. Parachironomus tenuicaudatus, Glyptotendipes senilis, Dicrotendipes modestus, Chironomus riparius, Chironomus entis/plumosus, Chironomus maturus, Chironomus crassicaudatus, Endochironomus subtendens, Cricotopus sylvestris, Cricotopus festivellus, Orthocladius obumbratus, Tanypus punctipennis, Rheotanytarsus exiguus gr., and Paratanytarsus nr. bituberculatus.

Genome-Resolved Metagenomic Analyses Reveal the Presence of a Putative Bacterial Endosymbiont in an Avian Nasal Mite (Rhinonyssidae; Mesostigmata)

Rhinonyssidae (Mesostigmata) is a family of nasal mites only found in birds. All species are hematophagous endoparasites, which may damage the nasal cavities of birds, and also could be potential reservoirs or vectors of other infections. However, the role of members of Rhinonyssidae as disease vectors in wild bird populations remains uninvestigated, with studies of the microbiomes of Rhinonyssidae being almost non-existent. In the nasal mite (Tinaminyssus melloi) from rock doves (Columba livia), a previous study found evidence of a highly abundant putatively endosymbiotic bacteria from Class Alphaproteobacteria. Here, we expanded the sample size of this species (two different hosts- ten nasal mites from two independent samples per host), incorporated contamination controls, and increased sequencing depth in shotgun sequencing and genome-resolved metagenomic analyses. Our goal was to increase the information regarding this mite species and its putative endosymbiont. We obtained a metagenome assembled genome (MAG) that was estimated to be 98.1% complete and containing only 0.9% possible contamination. Moreover, the MAG has characteristics typical of endosymbionts (namely, small genome size an AT bias). Overall, our results support the presence of a potential endosymbiont, which is the first described for avian nasal mites to date, and improve the overall understanding of the microbiota inhabiting these mites.

Molecular diet studies of water mites reveal prey biodiversity

Water mites are diverse aquatic invertebrates that provide potentially important ecosystem and economic services as bioindicators and mosquito biocontrol; however, little is known about water mite digestive physiology, including their diet in nature. Water mites, much like their spider relatives, liquefy their prey upon consumption. This results in the absence of morphologically identifiable prey in water mite mid-gut. Previous studies have reported associations in the field of water mites with presumed prey and laboratory observations of water mites feeding on specific organisms offered for ingestion; however, the present work aims to determine what water mites have ingested in nature based on molecular studies of gut contents from freshly collected organisms from the field. To elucidate water mite prey, we used next-generation sequencing to detect diverse cytochrome oxidase I DNA barcode sequences of putative prey in the guts of 54 specimens comprising two species of Lebertia and a few specimens of Arrenurus (2) and Limnesia (1). To our knowledge this is the first molecular study of the diets of water mites as they feed in nature. While the presence of chironomid DNA confirmed previous observations of midge larvae as part of the diets of Lebertia, we also found the DNA of diverse organisms in all four species of water mites, including the DNA of mosquitoes in 6 specimens of Lebertia and a large number of previously unknown prey, especially from oligochaete worms. These studies thereby reveal a greater diversity of prey and a potentially broader significance than previously appreciated for water mites in aquatic food webs. Molecular studies like this can detect water mite predators of mosquito larvae and add knowledge of water mite predatory contributions to freshwater food webs.

The Biodiversity of Water Mites That Prey on and Parasitize Mosquitoes

Water mites form one of the most biodiverse groups within the aquatic arachnid class. These freshwater macroinvertebrates are predators and parasites of the equally diverse nematocerous Dipterans, such as mosquitoes, and water mites are believed to have diversified as a result of these predatory and parasitic relationships. Through these two major biotic interactions, water mites have been found to greatly impact a variety of mosquito species. Although these predatory and parasitic interactions are important in aquatic ecology, very little is known about the diversity of water mites that interact with mosquitoes. In this paper, we review and update the past literature on the predatory and parasitic mite–mosquito relationships, update past records, discuss the biogeographic range of these interactions, and add our own recent findings on this topic conducted in habitats around the Laurentian Great Lakes. The possible impact on human health, along with the importance of water mite predator–prey dynamics in aquatic food webs, motivates an increase in future research on this aquatic predator and parasite and may reveal novel ecological functions that these parasitic and predator–prey relationships mediate.

Is the spatial distribution of lentic water mite assemblages (Acari: Hydrachnidia) governed by prey availability?

Predation is a biotic interaction that links water mites to different taxonomic groups of benthic invertebrates. Diptera larvae (Chironomidae) and microcrustaceans (Cladocera, Copepoda, Ostracoda) are known to be the most commonly preferred prey by water mites. Although these predatory interactions are known from observations and ex situ investigations, the distribution patterns and co-occurrence of water mites and their prey in littoral lentic habitats have been poorly studied. Our goal was to determine whether predation might serve as a significant factor in water mite assemblage composition and distribution. Samples were taken from littoral zones of 21 artificial lakes (reservoirs) in the Dinaric Western Balkan ecoregion of Croatia. At every site, 10 samples were collected with regard to shore slope in depth zones of up to 1 m. In total 490 samples were collected from April 2016 to July 2017. Data analysis showed that the spatial distribution of water mites was partially correlated with the environmental parameters we measured (explaining 45.1% of total water mite variation). A positive correlation between water mite abundance and diversity and depth gradient (favouring more stable conditions in deeper parts of the littoral zone) was also observed. Finally, water mite abundance and species richness variation were found to be best predicted by the abundance of potential prey groups. Predation was statistically determined to be a strong dispersion variable, most probably influencing both spatial distribution and composition of water mite assemblages.

First detection of prey DNA in Hygrobates fluviatilis (Hydrachnidia, Acari): a new approach for determining predator-prey relationships in water mites

Up to now our knowledge of water mite diet has been fragmentary. It is derived from observations in the field and laboratory or from a few selective laboratory experiments on food choice. In the present study, we were able to detect chironomid DNA in water mite bodies for the first time using molecular methods. Prey DNA was detected in virtually all Hygrobates fluviatilis (Hygrobatidae) that were fed on chironomid larvae after a starvation period of up to approximately 1 week. From the shortest interval (1 h after feeding) to the longest period after feeding (50 h) the relative amount of detected prey DNA was significantly reduced. In addition, there was a relationship between the relative amount of prey DNA and the assumed amount of the ingested prey (classified in categories of the dead prey which reflect the increasing ingestion of the mites and the decreasing body content of the prey individuals). The results of our study indicate that similar molecular analyses will be a powerful tool for diet investigations of mites from the field on various taxonomic resolutions of prey taxa. Moreover, the results of food selection experiments from the laboratory could be compared to evidence of predation by individuals from the field. For many mite taxa, especially ones which turned out to be difficult to breed in the laboratory (e.g. by unknown diet), the new methods might enable us to gain the first ever data on diet and thus may help us to consider the role of water mites in food webs more adequately in the future.

Distribution patterns and environmental correlates of water mites (Hydrachnidia, Acari) in peatland microhabitats

In Europe peatlands are wetlands of postglacial origin. Because of climatic changes and agricultural activities (i.e. drainage and peat extraction), they are one of the most endangered ecosystems worldwide. Water mites are well known as indicators of changing environments in other ecosystems such as springs and lakes. For our study we selected seven peatlands located in North-Western Poland and focused on water mite distribution and associated habitat and water quality variables. We described water mite fauna in various microhabitats (aquatic and semiaquatic) along the mineral-richness gradient to test whether this gradient is reflected in the composition of water mite assemblages. We selected conductivity, pH and vegetation as variables reflecting the poor-rich gradient. Additionally, we measured water depth, temperature and dissolved oxygen, which are often important parameters for water mites. We also noted presence of prey and host taxa of particular water mite species. Based on physicochemical parameters we identified three types of habitats harbouring three distinctive species groups of water mites. We were able to distinguish species that appear to be typical of spring fens (e.g. Hygrobates norvegicus, Lebertia separata), connected with acidic, nutrient poor pools (e.g. Arrenurus neumani, A. pustulator) and species seemingly typical of temporary habitats dominated by Sphagnum mosses (e.g. Piersigia intermedia, Zschokkea oblonga, A. stecki). The poor-rich gradient is strongly reflected in the composition of water mite assemblages. We also found strong correlations between the water mite fauna and both conductivity and pH gradient. Our results show that water conductivity is the most important of the examined factors, driving mite-species distribution in peatlands.

"Forms" of water mites (Acari: Hydrachnidia): intraspecific variation or valid species?

In many groups of organisms, especially in the older literature, it has been common practice to recognize sympatrically occurring phenotypic variants of a species as "forms". However, what these forms really represent often remains unclear, especially in poorly studied groups. With new algorithms for DNA-based species delimitation, the status of forms can be explicitly tested with molecular data. In this study, we test a number of what is now recognized as valid species of water mites (Hydrachnidia), but have in the past been treated as forms sympatrically occurring with their nominate species. We also test a form without prior taxonomical status, using DNA and morphometrics. The barcoding fragment of COI, nuclear 28S and quantitative analyses of morphological data were used to test whether these taxa merit species status, as suggested by several taxonomists. Our results confirm valid species. Genetic distances between the form and nominate species (Piona dispersa and Piona variabilis, COI 11%), as well as likelihood ratio tests under the general mixed-Yule coalescent model, supported that these are separately evolving lineages as defined by the unified species concept. In addition, they can be diagnosed with morphological characters. The study also reveals that some taxa genetically represent more than one species. We propose that P. dispersa are recognized as valid taxa at the species level. Unionicola minor (which may consist of several species), Piona stjordalensis, P. imminuta s. lat., and P. rotundoides are confirmed as species using this model. The results also imply that future studies of other water mite species complexes are likely to reveal many more genetically and morphologically distinct species.

The ecological effects of a herbicide-insecticide mixture on an experimental freshwater ecosystem

The effects of a co-occurring insecticide-herbicide mixture were evaluated using model ecosystems (microcosms) in the laboratory. Microcosms dosed with a high concentration (10 μg/L) of the insecticide terbufos, alone and as a mixture with the herbicide atrazine (25 μg/L), exhibited community level effects attributed to the elimination and decline of invertebrate populations, and also indirect effects. There were no community level effects at a lower concentration of terbufos (0.1 μg/L) alone or in a mixture with atrazine, although delayed population effects were observed. Female chironomids also emerged later and those from terbufos-only microcosms were smaller. Exposure to atrazine alone was also associated with lower abundances of cladocerans and reduced emergence of chironomids. The risk posed by atrazine is low and is unlikely to exacerbate the effects of terbufos. Nevertheless, the population-level effects highlight that terbufos poses a potential risk to aquatic ecosystems, regardless of whether atrazine is also present.

Can freshwater mites act as forensic tools?

Determination of post-mortem interval often employs analysis of age structure and diversity of saprophilic arthropods (including mites) that have colonized corpses. The majority of research has focused on decomposition processes in terrestrial situations, with relatively few studies on the utility of freshwater invertebrates as forensic agents. Most freshwater mites are predators, detritivores or algivores, and hence seem unlikely candidates as tools for aging or determining original placement of corpses or other bodily remains. The main exceptions to this are some aquatic Astigmata, which have occasionally been observed feeding on the tissues of moribund aquatic animals. Here I investigate Canadian law literature and published forensic research to determine how frequently freshwater mites are included in court cases or are found attending dead bodies. I found only one questionable report of aquatic mites in over 30 years of material from legal databases. Three published research papers reported mites associated with vertebrate flesh in fresh water. Only one paper provided an identification of mites finer than 'Acari' or 'water mites'. In this case, the mites were identified as Hydrozetes (Oribatida). In none of these papers were mites reported to be high in abundance or biomass, and in two of the three publications methodological problems and/or poor reporting of data raised doubts about interpretation of results. I conclude that based on their biology, there is little expectation that freshwater mites should be of great value as forensic tools, and this survey of legal and scientific literature supports my argument.

Parasitism of Sympetrum dragonflies by Arrenurus planus mites: maintenance of resistance particular to one species

Using field surveys and histological methods, we show that a dragonfly species (Sympetrum internum) has an effective resistance, not seen previously in other odonates, to a mite parasite (Arrenurus planus). This mite is a generalist parasite known to effectively engorge on several other odonate species. We argue that selection is likely weak, favouring counter adaptations of Arrenurus planus to Sympetrum internum, in part because other host species are available. We further argue that this pattern is possibly linked to the fact that the mode of resistance is relatively novel, and because Sympetrum internum is rare compared to another host species, Sympetrum obtrusum, at our study site. Although resistance of Sympetrum internum is quite effective against Arrenurus planus, Arrenurus planus larvae still attach to this species, but less often than they attach to Sympetrum obtrusum. Attachment to unsuitable hosts may reflect constraints operating on Arrenurus planus larvae during host discovery. Such factors influencing the evolution of resistance, when several potential host species exist, have not received much attention.