Behavioral aspects of host recognition by the symbiotic water mite Unionicola formosa (Acarina,Unionicolidae)

Summary The occurrence and specificity of host recognition behavior of adult and nymphal Unionicola formosa and the capability of adult mites to recolonize various mussel species were examined. Adult U. formosa aggregated on excised tissue from their host mussel, Anodonta imbecilis, in preference to that of two other species of mussels. Nymphs also exhibited an aggregation response to host tissue. A radioisotope (⁵¹Cr) technique was used to monitor the recolonization behavior of U. formosa. Adult female mites preferentially re-entered A. imbecilis rather than the sympatric mussel A. cataracta. The specificity of this behavior parallels the distribution of this water mite among potential bivalve hosts in the southeastern U.S. Host recognition by U. formosa may contribute to re-establishing contact with a host after accidental separation and probably helps to maintain mite-mussel symbioses. Whether or not larval U. formosa employ similar host recognition behavior while selecting a potential host has not as yet been determined.     

Competitive Exclusion,Harem Behaviour and Host Specificity of the Water Mite Unionicola ypsilophora (Hydrachnellae,Acari) Inhabiting Anodonta cygnea (Unionidae)

The co-occurring freshwater mussels Anodonta cygnea and A. anatina serve as hosts for the water mites Unionicola ypsilophora and U. intermedia, respectively. Male U. ypsilophora display a territorial behaviour. They fight with other males, and as a result, there is usually only one male per host. As a consequence, this intrasexual aggression results in female-defence polygyny, or a harem mating system. In contrast, U. intermedia shows no antagonistic behaviour between males. A. cygnea can serve as a host for U. intermedia, but this mite species apparently is excluded from the mussel by U. ypsilophora. In this way, U. intermedia is restricted by competitive exclusion to the mussel A. anatina.     

Parasite-host associations and life cycles of spring-living water mites (Hydrachnidia, Acari) from Luxembourg

Larval water mites are parasites of various insect species. The main aim of the present study was to analyse the host range of spring dwelling water mites. The investigation focuses on seven spring sites in Luxembourg. Some 24 water mite species were recorded either from the benthos or as parasites attached to flying insects captured in emergence traps. For 20 mite species 35 host species from four Nematocera (Diptera) families were recorded. About 80% of the host species and over 90% of the host individuals were Chironomidae, the others were Limoniidae, Dixidae and Simuliidae. For all water mite species recorded we present the observed host spectrum and/or potential hosts as well as the intensity of parasitism and the phenology of the mites. For 10 mite species the hosts were previously unknown. For another ten species the known host spectrum can be confirmed and extended. The host spectrum ranged from one host species (e.g. for Sperchon insignis) to at least 10 host species (for Sperchon thienemanni, Ljania bipapillata), but the effective host range could not be definitively estimated due to the lack of corresponding data. The hypothesised host preference of the water mites, of which most are strictly confined to spring habitats, for similarly spring-preferring hosts could not be proven. The mean intensity of parasitism was highest for Thyas palustris (10.8 larvae/host) and lowest for Sperchon insignis and Hygrobates norvegicus (1.2 larvae per host for each). The hydryphantid mite Thyas palustris occurred at maximal intensity (41 larvae per host) and the two abdominal parasites Ljania bipapillata and Arrenurus fontinalis showed higher mean intensities than the thoracic parasites did. Larval water mites parasitising chironomids did not exhibit a preference for host sex. The phenology of the larval mite species was varied, some species were only present in samples early in the year and others exclusively in the summer. Another species showed two peaks of occurrence, springtime/early summer and late summer/autumn. In conclusion, the water mite larvae in the studied springs showed differences in host spectra and phenology but there are no clear evidences in both for host partitioning. Maybe, the relative low species diversity of water mites in individual springs and the low inter-specific competition for suitable hosts in combination with the high host abundances and species richness makes springs such favourable habitats for the mites.     

The symbiotic water mite Unionicola formosa (Acari: Unionicolidae) ingests mucus and tissue of its molluscan host

Unionicola formosa is a symbiotic water mite that passes most of its life cycle in the mantle cavity of freshwater mussels. Although mites of this genus are often referred to as parasitic, little is known about their nutritional biology. A few species reportedly pierce the gill of a host mussel and ingest tissue or hemolymph. The present study was undertaken to identify possible sources of nutrition for U. formosa. To determine if mites ingested particulate matter in the mucous strand produced by a mussel during feeding, mussels with resident mites were exposed to a suspension of fluorescent microspheres. There was no evidence that U. formosa ingested the beads. Histochemical staining did, however, indicate a mucous material present in the midgut of the mites. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic assays revealed a high molecular weight component, consistent with a mucopolysaccharide, present both in the mussel gill and the mites. Results from western blots and an immunoaffinity binding assay with antibodies against mussel gill tissue and hemolymph also indicated that mites ingested host tissue. Whereas U. formosa probably does not ingest particulate material acquired by its host's suspension feeding, it is apparent that this mite utilizes host mucus, gill tissue, or hemolymph for at least part of its nutrition.     

Causal mechanisms underlying host specificity in bat ectoparasites

In parasites, host specificity may result either from restricted dispersal capacity or from fixed coevolutionary host-parasite adaptations. Knowledge of those proximal mechanisms leading to particular host specificity is fundamental to understand host-parasite interactions and potential coevolution of parasites and hosts. The relative importance of these two mechanisms was quantified through infection and cross-infection experiments using mites and bats as a model. Monospecific pools of parasitic mites (Spinturnix myoti and S. andegavinus) were subjected either to individual bats belonging to their traditional, native bat host species, or to another substitute host species within the same bat genus (Myotis). The two parasite species reacted differently to these treatments. S. myoti exhibited a clear preference for, and had a higher fitness on, its native host, Myotis myotis. In contrast, S. andegavinus showed no host choice, although its fitness was higher on its native host M. daubentoni. The causal mechanisms mediating host specificity can apparently differ within closely related host-parasite systems.     

Review Geographic differences in host specialization between the symbiotic water mites Unionicola formosa and Unionicola foili (Acari: Unionicolidae)

The host specificity and population genetic structure of the symbiotic water mites Unionicola foili from the host mussel Utterbackia imbecillis and Unionicola formosa from the mussels Pyganodon cataracta, Pyganodon grandis and Anodonta suborbiculata were examined over a broad geographical scale in order to determine the extent to which specialization by these water mites is structured geographically. The behavioural responses of U. foili and U. formosa were highly host-species specific, with adults of both species exhibiting negative phototaxis in the presence of a chemical factor from the species of mussel with which the mites had been associated in the field. The photobehaviour of these water mites in the presence of water from a non-host mussel varied depending on the species in question. Although U. foili from U. imbecillis exhibited negative phototaxis in water modified by A. suborbiculata, mites from this latter host did not exhibit a directional response in U. imbecillis water. Unionicola foili and U. formosa from A. suborbiculata were positively phototactic when they were exposed to water modified by either species of Pyganodon. The photoresponse of U. formosa from P. cataracta and P. grandis was positive in the presence of water modified by U. imbecillis and A. suborbiculta. However, these mussel-mites showed no directional response in water modified by their alternate species of Pyganodon. Unionicola foili and the host-associated populations of U. formosa were examined for allozyme variation at eight loci to determine the pattern and degree of genetic variation. There was a high degree of genetic differentiation when mite populations from the two species of Pyganodon were compared with U. foili or U. formosa from A. suborbiculata. These populational groupings were fixed for different alleles at two enzyme loci. The results of this study indicate that populations of U. formosa from P. cataracta and P. grandis are reproductively isolated from U. foili from U. imbecillis and from U. formosa from A. suborbiculata and contend that host specificity is an important mechanism in restricting gene flow among these populational groupings. Furthermore, this study indicates that specialization among unionicolid water mites can vary geographically, owing to differences in geographic distribution of available hosts and differences in host use.Exp Appl Acarol 22: 683697 © 1998 Kluwer Academic Publishers     

Host species preferences by bitterling, Rhodeus sericeus, spawning in freshwater mussels and consequences for offspring survival

Two hypotheses have been advanced to explain the evolution of host responses to parasites: the arms race-evolutionary lag and equilibrium hypotheses. We investigated predictions from these hypotheses based on interspecies host preferences and adaptations in an obligate spawning relationship between a freshwater fish, the European bitterling (Cyprinidae) and four species of freshwater mussels (Unionidae), which the fish use as hosts for their eggs. We found a significant trend in preference by the fish for mussels in the following order: Unio pictorum, U. tumidus, Anodonta anatina and A. cygnea. Male and female bitterling both showed this ranking and the clutch sizes deposited into each species also followed this trend. These host preferences proved to be adaptive in terms of egg ejection, which was lowest in the most preferred species (U. pictorum). Furthermore, these hierarchical host preferences were flexible, as females switched species when individuals of the preferred species ejected a greater number of eggs. The similarity in mussel defences between the U.K. population and a European population of ancient sympatry suggests that the absence of a defence in some mussel species may not be due to evolutionary lag. Mussel ejection behaviour may have reached an evolutionary equilibrium in each host species, or alternatively the fish may have evolved adaptive preferences that coincide with generalized mussel responses to foreign objects in their gills. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Random amplified polymorphic DNA analysis of kinship within host-associated populations of the symbiotic water mite Unionicola foili (Acari: Unionicolidae)

Kinship relations within populations of unionicolid water mites are not well known, owing to their complex life cycles and the fact that interactions between active and resting stages for some species are transitory. A number of species of unionicolid water mites are, however, obligate symbionts of freshwater mussels and spend most of their life cycle in association with these hosts. Among these species of mites, parents and offspring are more likely to co-occur and thus provide opportunities to address questions related to the structure of the mating system. The present study employs random amplified polymorphic DNA (RAPD) analysis to address kinship within populations of Unionicola foili living in symbiotic association with the host mussel Utterbackia imbecillis. DNA was amplified from adult mites and a representative number of eggs or larvae (n = 20-30) that were removed from mussels collected on three separate occasions (July, November, and March) over a 12-month period. Parsimony analyses of the molecular data for adults and progeny collected from mussels during July, November, and March revealed distinct groupings, that for the most part, corresponded to mites collected from each of the sampling periods. Many of the genetic markers obtained for male and female U. foili were not evident among the larvae or eggs, suggesting that adults obtained from a host mussel at the time of collection were not the parents of a majority of the progeny. However, female mites and eggs collected from mussels during March and November shared more markers than did females and progeny examined during July. Furthermore, many offspring in the July sampling period were found to have one or more parents absent from the sampled population. Overall, RAPD profiling appears to have limited usage in determining kinship within populations of U. foili, due to its recruitment patterns, and the relatively large number of adults and progeny per mussel. It may, however, prove to be a useful method for assessing genetic relatedness among unionicolid mussel-mites that have substantially lower population densities.     

Phoretic Poecilochirus mites specialize on their burying beetle hosts

Recurring species interactions can cause species to adapt to each other. Specialization will increase the fitness of symbionts in the coevolved association but may reduce the flexibility of symbiont choice as it will often decrease fitness in interactions with other than the main symbiont species. We analyzed the fitness interactions between a complex of two cryptic mite species and their sympatric burying beetle hosts in a European population. Poecilochirus mites (Mesostigmata, Parasitidae) are phoretic on burying beetles and reproduce alongside beetles, while these care for their offspring at vertebrate carcasses. While Poecilochirus carabi is typically found on Nicrophorus vespilloides beetles, P. necrophori is associated with N. vespillo. It has long been known that the mites discriminate between the two beetle species, but the fitness consequences of this choice remained unknown. We experimentally associated both mite species with both beetle species and found that mite fitness suffered when mites reproduced alongside a nonpreferred host. In turn, there is evidence that one of the beetle species is better able to cope with the mite species they are typically associated with. The overall fitness effect of mites on beetles was negative in our laboratory experiments. The Poecilochirus mites studied here are thus specialized competitors or parasites of burying beetles.     

Competition between mobile species using patchy resources: an example from a freshwater,symbiotic assemblage

Summary Three species of freshwater mites that are symbiotic with mussels in St Mark's River, north Florida, have consistently high rates of colonization to and occupy high proportions of mussels. The mites Unionicola poundsi and U. serrata are territorial and have limited numbers/host, whereas the non-territorial U. abnormipes has highly variable numbers/host. U. abnormipes and U. serrata are most common in Villosa villosa and Uniomerus declivis respectively, patterns that can not be explained by host species preferences, whereas U. poundsi is equally abundant in both host species. Field experiments showed that both U. poundsi and U. serrata were limited most by intraspecific competition between adult mites, presumably for access to food and oviposition sites. Additionally, U. serrata did not remain within small hosts, most of which were V. villosa. In contrast, numbers of U. abnormipes were limited by both other mite species although the nature of the interactions differed. U. serrata may prey on U. abnormipes when they co-occur, whereas U. poundsi probably only excludes U. abnormipes from certain areas within hosts. Hence, U. abnormipes occurs mostly in V. villosa because most of these mussels do not contain U. serrata, but even so its numbers are still depressed by U. poundsi. The results were consistent with the general expectation of Holmes and Price (1986) that parasite assemblages where species have high colonization levels should be organized primarily by biotic interactions. However, specific outcomes of competition between mites were consistent with the more general model of Levins (1979) for competition between species using variable resources. Failure of other models to apply to Unionicola pinpointed at least five key biological characters that may form a better basis of comparison than taxonomic or habitat-based contrasts.     

Population size and structure of three mussel species (Bivalvia: Unionidae) in a northeastern German river with special regard to influences of environmental factors

Unionid mussels are of great ecological importance in running and standing waters, however their populations declined continually during the 20th century. In order to collect more data on the situation of these mussels in running waters, the populations of Anodonta anatina, Anodonta cygnea, and Unio tumidus (Unionidae) were investigated in the northeastern German river Ryck from 1996 to 1998. At three sampling stations along the river, the mussel stocks as well as sediment and water properties were analyzed. In this river abundances of up to 138.7 indiv./m² were detected. The average population densities varied from 10.9 to 34.9 indiv./m². More critically however, the age structures showed significant signs of irregular reproductive success and overaging. Consequently, the mussel stocks are going to decline, and furthermore, U.tumidus should be listed as an endangered species in the Ryck river. Negative influences on bivalves can be expected from sporadically occurring low oxygen and high ion concentrations in the water. But after all, the conditions within the sediments seem to be decisive for the survival of juvenile mussels and thus for the age structure of the populations.     

Factors influencing host choice of the honey bee parasite Varroa jacobsoni Oud

Reproducing Varroa jacobsoni obtained from brood cells of Apis mellifera L. with 13–16 day old bees (pupae) and Varroa mites kept on adult bees for at least 8 days were simultaneously tested for their choice in three host types. Comparisons were made of attractiveness of Varroa jacobsoni to nurse bees, pollen foragers as to larvae from nearly capped brood cells. Host choices were observed in Petri dishes and in an Y-shaped olfactometer. Varroa jacobsoni obtained from capped brood cells showed a stronger preference for nurse bees in Petri dish simultaneous choice tests with pollen foragers or larvae than did mites which were previously kept on adult bees. In olfactometer simultaneous choice tests, the two mite test groups showed no clear difference in preferences for bees of different ages. The preference of Varroa jacobsoni for bees of different ages is therefore not only influenced by host factors but also by intrinsic factors in female mites that depend on the mite's reproductive stage.     

Altered host plant preference of Tetranychus urticae and prey preference of its predator Phytoseiulus persimilis (Acari: Tetranychidae, Phytoseiidae) on transgenic Cry3Bb-eggplants

The behavior of the two-spotted spider mite, Tetranychus urticae Koch and the predatory mite Phytoseiulus persimilis A.-H. was investigated in laboratory experiments with transgenic Bt-eggplants, Solanum melongena L., producing the Cry3Bb toxin and corresponding isogenic, non-transformed eggplants. In bitrophic experiments, dual-choice disc tests were conducted to reveal the effects of transgenic eggplants on host plant preference of T. urticae. Adult spider mite females were individually placed on leaf discs (2 cm diameter) and were observed during five days. Females occurred significantly more frequently on transgenic halves on which also significantly more T. urticae eggs were found. The effects of a Cry3Bb-eggplant fed prey on the feeding preference of P. persimilis were investigated in tritrophic experiments. Sixteen spider mite females, eight of which had been taken from transgenic and eight from isogenic eggplants, were offered to well-fed females of P. persimilis and numbers of respective spider mites consumed were registered 12 h later when the predators were offered new spider mites again. This procedure was repeated six times. The results revealed that predatory mites consumed significantly less Bt-fed spider mites than prey that had been raised on control eggplants. These results indicate that eggplants expressing the Cry3Bb toxin for resistance against the Colorado potato beetle are more preferred by spider mites but are less preferred by their predator P. persimilis. Possible consequences of these findings for biological control of spider mites on eggplants are discussed.     

A possible evolutionary lag in the relationship between freshwater mussels and European bitterling

The coevolutionary dynamics between European bitterling Rhodeus amarus and freshwater unionid mussels, which the former parasitize by laying eggs on their gills, were tested. In a series of experiments fish preferences and mussel responses were compared in parasites and hosts of recent (Europe) and ancient (Asia) sympatry. Rhodeus amarus readily oviposited on the gills of all mussel species tested. Fish that laid their eggs on the gills of Asian Anodonta woodiana, however, suffered a dramatic reduction in reproductive success compared to fish that oviposited on the gills of European mussels: Unio pictorum , Unio tumidus , Anodonta anatina and Anodonta cygnea . This difference was the result of egg ejection behaviour by mussels rather than the unsuitability of the internal gill environment for European bitterling embryo development. The ejection response of mussels with a long sympatry with European bitterling was considerably more pronounced than that of mussels with a substantially shorter sympatry. The data support a coevolutionary arms race between bitterling and mussels and point to an evolutionary lag in the relationship between R. amarus and its European mussel hosts.     

Avoidance of host resistance in the oviposition-site preferences of rose bitterling

A contemporary outcome of dynamic host–parasite coevolution can be driven by the adaptation of a parasite to exploit its hosts at the population and species levels (parasite specialisation) or by local host adaptations leading to greater host resistance to sympatric parasite populations (host resistance). We tested the predominance of these two scenarios using cross-infection experiments with two geographically distant populations of the rose bitterling, Rhodeus ocellatus, a fish brood parasite of freshwater mussels, and four populations of their mussel hosts (two Anodonta woodiana and two Unio douglasiae populations) with varying degrees of geographic sympatry and local coexistence. Our data support predictions for host resistance at the species level but no effect of local coexistence between specific populations. Rhodeus ocellatus showed a preference for allopatric host populations, irrespective of host species. Host mussel response, in terms of ejection of R. ocellatus eggs, was stronger in the more widespread and abundant host species (A. woodiana) and this response tended to be higher in sympatric populations. These outcomes provide support for the importance of host resistance in bitterling oviposition-site decisions, demonstrating that host choice by R. ocellatus is adaptive by minimizing egg ejections. These findings imply that R. ocellatus, and potentially other bitterling species, may benefit from exploiting novel hosts, which may not possess appropriate adaptive responses to parasitism.     

Bayesian inference supports the host selection hypothesis in explaining adaptive host specificity by European bitterling

Generalist parasites have the capacity to infect multiple hosts. The temporal pattern of host specificity by generalist parasites is rarely studied, but is critical to understanding what variables underpin infection and thereby the impact of parasites on host species and the way they impose selection on hosts. Here, the temporal dynamics of infection of four species of freshwater mussel by European bitterling fish (Rhodeus amarus) was investigated over three spawning seasons. Bitterling lay their eggs in the gills of freshwater mussels, which suffer reduced growth, oxygen stress, gill damage and elevated mortality as a result of parasitism. The temporal pattern of infection of mussels by European bitterling in multiple populations was examined. Using a Bernoulli Generalized Additive Mixed Model with Bayesian inference it was demonstrated that one mussel species, Unio pictorum, was exploited over the entire bitterling spawning season. As the season progressed, bitterling showed a preference for other mussel species, which were inferior hosts. Temporal changes in host use reflected elevated density-dependent mortality in preferred hosts that were already infected. Plasticity in host specificity by bitterling conformed with the predictions of the host selection hypothesis. The relationship between bitterling and their host mussels differs qualitatively from that of avian brood parasites.     

Host–parasite interactions and vectors in the barn swallow in relation to climate change

Recent climate change has affected the phenology of numerous species, and such differential changes may affect host–parasite interactions. Using information on vectors (louseflies, mosquitoes, blackflies) and parasites (tropical fowl mite Ornithonyssus bursa, the lousefly Ornithomyia avicularia, a chewing louse Brueelia sp., two species of feather mites Trouessartia crucifera and Trouessartia appendiculata, and two species of blood parasites Leucozytozoon whitworthi and Haemoproteus prognei) of the barn swallow Hirundo rustica collected during 1971–2008, I analyzed temporal changes in emergence and abundance, relationships with climatic conditions, and changes in the fitness impact of parasites on their hosts. Temperature and rainfall during the summer breeding season of the host increased during the study. The intensity of infestation by mites decreased, but increased for the lousefly during 1982–2008. The prevalence of two species of blood parasites increased during 1988–2008. The timing of first mass emergence of mosquitoes and blackflies advanced. These temporal changes in phenology and abundance of parasites and vectors could be linked to changes in temperature, but less so to changes in precipitation. Parasites had fitness consequences for hosts because intensity of the mite and the chewing louse was significantly associated with delayed breeding of the host, while a greater abundance of feather mites was associated with earlier breeding. Reproductive success of the host decreased with increasing abundance of the chewing louse. The temporal decrease in mite abundance was associated with advanced breeding of the host, while the increase in abundance of the lousefly was associated with earlier breeding. Virulence by the tropical fowl mite decreased with increasing temperature, independent of confounding factors. These findings suggest that climate change affects parasite species differently, hence altering the composition of the parasite community, and that climate change causes changes in the virulence of parasites. Because the changing phenology of different species of parasites had both positive and negative effects on their hosts, and because the abundance of some parasites increased, while that of other decreased, there was no consistent temporal change in host fitness during 1971–2008.     

Fouling of European freshwater bivalves (Unionidae) by the invasive zebra mussel (Dreissena polymorpha)

1. The zebra mussel (Dreissena polymorpha) is well known for its invasive success and its ecological and economic impacts. Of particular concern has been the regional extinction of North American freshwater mussels (Order Unionoida) on whose exposed shells the zebra mussels settle. Surprisingly, relatively little attention has been given to the fouling of European unionoids. 2. We investigated interspecific patterns in fouling at six United Kingdom localities between 1998 and 2008. To quantify the effect on two pan‐European unionoids (Anodonta anatina and Unio pictorum), we used two measures of physiological status: tissue mass : shell mass and tissue glycogen content. 3. The proportion of fouled mussels increased between 1998 and 2008, reflecting the recent, rapid increase in zebra mussels in the U.K. Anodonta anatina was consistently more heavily fouled than U. pictorum and had a greater surface area of shell exposed in the water column. 4. Fouled mussels had a lower physiological condition than unfouled mussels. Unlike tissue mass : shell mass ratio, tissue glycogen content was independent of mussel size, making it a particularly useful measure of condition. Unio pictorum showed a stronger decline in glycogen with increasing zebra mussel load, but had a broadly higher condition than A. anatina at the time of study (July). 5. Given the high conservation status and important ecological roles of unionoids, the increased spatial distribution and fouling rates by D. polymorpha in Europe should receive more attention.     

Random amplified polymorphic DNA analysis of kinship within host-associated populations of the symbiotic water mite Unionicola foili (Acari: Unionicolidae)

Kinship relations within populations of unionicolid water mites are not well known, owing to their complex life cycles and the fact that interactions between active and resting stages for some species are transitory. A number of species of unionicolid water mites are, however, obligate symbionts of freshwater mussels and spend most of their life cycle in association with these hosts. Among these species of mites, parents and offspring are more likely to co-occur and thus provide opportunities to address questions related to the structure of the mating system. The present study employs random amplified polymorphic DNA (RAPD) analysis to address kinship within populations of Unionicola foili living in symbiotic association with the host mussel Utterbackia imbecillis. DNA was amplified from adult mites and a representative number of eggs or larvae (n = 20-30) that were removed from mussels collected on three separate occasions (July, November, and March) over a 12-month period. Parsimony analyses of the molecular data for adults and progeny collected from mussels during July, November, and March revealed distinct groupings, that for the most part, corresponded to mites collected from each of the sampling periods. Many of the genetic markers obtained for male and female U. foili were not evident among the larvae or eggs, suggesting that adults obtained from a host mussel at the time of collection were not the parents of a majority of the progeny. However, female mites and eggs collected from mussels during March and November shared more markers than did females and progeny examined during July. Furthermore, many offspring in the July sampling period were found to have one or more parents absent from the sampled population. Overall, RAPD profiling appears to have limited usage in determining kinship within populations of U. foili, due to its recruitment patterns, and the relatively large number of adults and progeny per mussel. It may, however, prove to be a useful method for assessing genetic relatedness among unionicolid mussel-mites that have substantially lower population densities.     

The relations between mites of the genus Unionicola and the mussels Anodonta and Unio

The locations in mussels of four species of watermites, Unionicola aculeata, U. bonzi, U. intermedia and U. ypsilophora and their degrees of parasitism have been compared. Unionicola aculeata and U. bonzi do not live parasitic and need Anodonta anatina and Unio pictorum respectively as a shelter for their transformation stages. Unionicola intermedia and U. ypsilophora live parasitic on the gills of Anodonta anatina and A. cygnea respectively. Every female of Unionicola ypsilophora has a territory in the mussel, as contrasted with U. intermedia, many females of which are found together. The consequences for the population density are discussed.Zoological Laboratory, University of Amsterdam