Analysis of Sarcoptes scabiei finds no evidence of infection with Wolbachia

The endosymbiont Wolbachia has been detected in a range of filarial nematodes and parasitic mites and is known to affect host reproductive compatibility and potentially evolutionary processes. PCR of Wolbachia surface protein (wsp), ftsZ and 16SrRNA genes from individual Sarcoptes scabiei mites obtained from a series of individual hosts, and database searches of an S. scabiei var. hominis EST library failed to detect Wolbachia genes. Therefore, Wolbachia appears not to be involved in the genetic subdivision observed between varieties of host-associated S. scabiei or, involved in the inflammatory disease pathogenesis of scabies unlike its activity in filarial infection.     

High-resolution melt analysis for the detection of a mutation associated with permethrin resistance in a population of scabies mites

Permethrin as a topical acaricide cream is widely used to treat scabies. The neuronal voltage-sensitive sodium channel (Vssc), necessary for the generation of action potentials in excitable cells, is the target of pyrethroid acaricides such as permethrin. Pyrethroid resistance has been linked to specific mutations in the Vssc gene. Following the partial sequencing of the Vssc gene in the scabies mite Sarcoptes scabiei (L.) (Astigmata: Sarcoptidae), we compared Vssc gene sequences from permethrin-sensitive and -tolerant S. scabiei var. canis Gerlach mites, and identified a G to A single nucleotide polymorphism (SNP) in permethrin-tolerant mites resulting in an amino acid change from glycine to aspartic acid in domain III S6. The mutation is in a region of the gene where mutations have been identified in a range of pyrethroid-resistant arthropods. Results of in vitro permethrin exposure assays showed that survival rates for mites bearing the mutation were similar to those previously reported for mites from human subjects where clinical tolerance to permethrin had been observed. A real-time polymerase chain reaction-high-resolution melt (PCR-HRM) assay was developed to detect this SNP. This assay provides a useful methodology for screening for this and other mutations associated with permethrin resistance in scabies mite populations and thus facilitates surveillance for acaricide resistance.     

Mitochondrial Genome Sequence of the Scabies Mite Provides Insight into the Genetic Diversity of Individual Scabies Infections

The scabies mite, Sarcoptes scabiei, is an obligate parasite of the skin that infects humans and other animal species, causing scabies, a contagious disease characterized by extreme itching. Scabies infections are a major health problem, particularly in remote Indigenous communities in Australia, where co-infection of epidermal scabies lesions by Group A Streptococci or Staphylococcus aureus is thought to be responsible for the high rate of rheumatic heart disease and chronic kidney disease. We collected and separately sequenced mite DNA from several pools of thousands of whole mites from a porcine model of scabies (S. scabiei var. suis) and two human patients (S. scabiei var. hominis) living in different regions of northern Australia. Our sequencing samples the mite and its metagenome, including the mite gut flora and the wound micro-environment. Here, we describe the mitochondrial genome of the scabies mite. We developed a new de novo assembly pipeline based on a bait-and-reassemble strategy, which produced a 14 kilobase mitochondrial genome sequence assembly. We also annotated 35 genes and have compared these to other Acari mites. We identified single nucleotide polymorphisms (SNPs) and used these to infer the presence of six haplogroups in our samples, Remarkably, these fall into two closely-related clades with one clade including both human and pig varieties. This supports earlier findings that only limited genetic differences may separate some human and animal varieties, and raises the possibility of cross-host infections. Finally, we used these mitochondrial haplotypes to show that the genetic diversity of individual infections is typically small with 1–3 distinct haplotypes per infestation.     

Redundant species, cryptic host-associated divergence, and secondary shift in Sennertia mites (Acari: Chaetodactylidae) associated with four large carpenter bees (Hymenoptera: Apidae: Xylocopa) in the Japanese island arc

Sennertia mites live as inquilines in the nests of carpenter bees and disperse as deutonymphs on newly emerged adult bees. Because their life cycle is tightly linked to that of the host bees, Sennertia may diverge in response to speciation in the hosts. However, the majority of Sennertia species are associated with several closely related carpenter bees, suggesting that host speciation may not be reflected in mite genetic structure. Here we investigate the extent of host-associated genetic differentiation in two Sennertia mites (S. alfkeni and S. japonica) that share four closely related, strictly allopatric large carpenter bees (Xylocopa). Analysis of the mitochondrial cytochrome oxidase subunit I (COI) gene in Sennertia unexpectedly indicates that the two species represent morphological variants of a single species, and they collectively group into four distinct, allopatric clades that are uniquely associated with a single Xylocopa host. An exception is the mites associated with X. amamensis of the northernmost populations, which have genotypes typical of those associated with neighboring X. appendiculatacircumvolans. Additional analysis using amplified fragment length polymorphism (AFLP) further corroborates the presence of four mite clades but contrary to the COI data, suggests that the mites of the southernmost population of X. appendiculatacircumvolans have genetic profiles typical of those associated with X. amamensis. These results indicate that some mites have undergone secondary host switch after the formation of the four mite lineages and further experienced mitochondrial introgression during period of lineage coexistence. Overall, our results strongly urge reappraisal of deutonymph-based mite taxonomy and illuminate the importance of host-associated divergence during incipient stage of speciation in chaetodactylid mites. Furthermore, the occurrence of host switch and introgression between genetically differentiated mites entails that two host species have co-occurred in the past, thus providing a unique source of evidence for migration and competitive exclusion between the presently allopatric Xylocopa hosts.     

Morphological and molecular comparison of host-derived populations of parasitic Psoroptes mites

Infestation by parasitic Psoroptes mites (Acari: Psoroptidae) is an important cause of economic loss and welfare problems in livestock in many areas of the world. At least five species within this genus have been recognized, based on the host infested, the infestation site and differences in length of the opisthosomal setae of adult male mites. Here the integrity of these species is considered by subjecting populations of mites from a range of host species and geographical locations to simultaneous morphological and molecular genetic analyses. Morphological analysis showed that there were significant differences in shape and size between mite populations from different hosts, and that length of the outer opisthosomal setae in males and the homologous seta in females were the most important distinguishing character in adults. However, considerable variation in outer opisthosomal seta length was evident within and between populations of mites, and differences were not clearly related to host-species or geographical origin and did not support the accepted species differences. Molecular characterization using sequence data from the mitochondrial second internal transcribed spacer (ITS-2) region and microsatellite markers found little or no consistent host-related variation between the mite population samples. The results suggest that there is no case for considering the Psoroptes mites from the different hosts examined as separate species and that the morphological variation observed therefore may represent phenotypic adaptation to the local microenvironment on particular species of host.     

Functional analysis and localisation of a delta-class glutathione S-transferase from Sarcoptes scabiei

The mite Sarcoptes scabiei causes sarcoptic mange, or scabies, a disease that affects both animals and humans worldwide. Our interest in S. scabiei led us to further characterise a glutathione S-transferase. This multifunctional enzyme is a target for vaccine and drug development in several parasitic diseases. The S. scabiei glutathione S-transferase open reading frame reported here is 684 nucleotides long and yields a protein with a predicted molecular mass of 26 kDa. Through phylogenetic analysis the enzyme was classified as a delta-class glutathione S-transferase, and our paper is the first to report that delta-class glutathione S-transferases occur in organisms other than insects. The recombinant S. scabiei glutathione S-transferase was expressed in Escherichia coli via three different constructs and purified for biochemical analysis. The S. scabiei glutathione S-transferase was active towards the substrate 1-chloro-2,4-dinitrobenzene, though the positioning of fusion partners influenced the kinetic activity of the enzyme. Polyclonal antibodies raised against S. scabiei glutathione S-transferase specifically localised the enzyme to the integument of the epidermis and cavities surrounding internal organs in adult parasites. However, some minor staining of parasite intestines was observed. No staining was seen in host tissues, nor could we detect any antibody response against S. scabiei glutathione S-transferase in sera from naturally S. scabiei infected dogs or pigs. Additionally, the polyclonal sera raised against recombinant S. scabiei glutathione S-transferase readily detected a protein from mites, corresponding to the predicted size of native glutathione S-transferase.     

The complete mitochondrial genome of Sarcoptes scabiei var. nyctereutis from the Japanese raccoon dog: Prediction and detection of two transfer RNAs (tRNA-A and tRNA-Y)

Sarcoptes scabiei (Acari: Sarcoptidae) causes a common contagious skin disease that affects many mammals. Here, the complete mitochondrial genome of a mite, S. scabiei var. nyctereutis, from Japanese wild raccoon dogs was analyzed. The 13,837 bp circular genome contained 13 protein-coding genes, two rRNA genes, and 22 tRNA genes. For the first time, two tRNAs (alanine and tyrosine), that were thought to be absent in scabies mites from other animals, were predicted to have short, non-cloverleaf structures by in silico annotation and detected by RT-PCR, sequencing, and northern analysis. The mitochondrial genome structure of S. scabiei is similar to that of Psoroptes cuniculi and Dermatophagoides farinae. While small and unusual tRNA genes seem to be common among acariform mites, further experimental evidence for their presence is needed. Furthermore, through an analysis of the cox1 gene, we have provided new evidence to confirm the transmission of this mite between different animal hosts.     

Spatio-temporal population genetic structure of the parasitic mite Spinturnix bechsteini is shaped by its own demography and the social system of its bat host

Information about the population genetic structures of parasites is important for an understanding of parasite transmission pathways and ultimately the co-evolution with their hosts. If parasites cannot disperse independently of their hosts, a parasite's population structure will depend upon the host's spatial distribution. Geographical barriers affecting host dispersal can therefore lead to structured parasite populations. However, how the host's social system affects the genetic structure of parasite populations is largely unknown. We used mitochondrial DNA (mtDNA) to describe the spatio-temporal population structure of a contact-transmitted parasitic wing mite ( Spinturnix bechsteini ) and compared it to that of its social host, the Bechstein's bat ( Myotis bechsteinii ). We observed no genetic differentiation between mites living on different bats within a colony. This suggests that mites can move freely among bats of the same colony. As expected in case of restricted inter-colony dispersal, we observed a strong genetic differentiation of mites among demographically isolated bat colonies. In contrast, we found a strong genetic turnover between years when we investigated the temporal variation of mite haplotypes within colonies. This can be explained with mite dispersal occuring between colonies and bottlenecks of mite populations within colonies. The observed absence of isolation by distance could be the result from genetic drift and/or from mites dispersing even between remote bat colonies, whose members may meet at mating sites in autumn or in hibernacula in winter. Our data show that the population structure of this parasitic wing mite is influenced by its own demography and the peculiar social system of its bat host.     

The parasite-host specificity of the itch mite Sarcoptes scabiei (Acariformes: Sarcoptidae) in man and animals (a review of the literature)]

The primary parasitic relations between the itch mite Sarcoptes scabiei (L.) and man are confirmed indirectly by the presence in the family Sarcoptidae of close genera, members of which parasitize primates. Judging from the composition of domestic and wild animals-hosts, the source of their infection with S. scabiei was man that gave rise to numerous forms of mites specific to individual species of hosts or their related groups belonging to different taxonomic ranks. Three types of host relations and, accordingly, forms of sarcoptosis are suggested at the infection from an alien host: pseudosarcoptosis, temporary self-curable and typical lingering sarcoptosis. The ways of reinfection, invasiveness of stages of the mite and clinical picture for each form of the disease are analyzed.     

Knoxdaviesia capensis: dispersal ecology and population genetics of a flower-associated fungus

Protea-associated fungi are dispersed between flower heads by mites, beetles and possibly birds. For the ophiostomatoid fungus, Knoxdaviesia proteae, these vectors offer regular dispersal between distant floral hosts. Unlike K. proteae, Knoxdaviesia capensis occupies multiple Protea host species. In this study, we aimed to determine whether the generalist K. capensis shares the long-distance dispersal pattern with specialist K. proteae and whether it moves freely between different host species. We evaluated the genetic structure of K. capensis from five populations of a wide-spread host and between sympatric hosts. Twelve K. capensis-specific microsatellite markers were developed and applied to 90 individuals. K. capensis showed high genetic diversity and almost maximal genotypic diversity. All populations were poorly differentiated, indicating the presence of long-distance dispersal. No differentiation could be detected between sympatric host populations, suggesting free dispersal between different hosts. This implies that the beetle and bird vectors that pollinate Protea species show the same non-specific movement.     

Pleistocene isolation, secondary introgression and restricted contemporary gene flow in the pig-eye shark, Carcharhinus amboinensis across northern Australia

We examine the structure and phylogeography of the pig-eye shark (Carcharhinus amboinensis) common in shallow coastal environments in northern Australia using two types of genetic markers, two mitochondrial (control region and NADH hydrogenase 4) and two nuclear (microsatellite and Rag 1) DNA. Two populations were defined within northern Australia on the basis of mitochondrial DNA evidence, but this result was not supported by nuclear microsatellite or Rag 1 markers. One possibility for this structure might be sex-specific behaviours such as female philopatry, although we argue it is doubtful that sufficient time has elapsed for any potential signatures from this behaviour to be expressed in nuclear markers. It is more likely that the observed pattern represents ancient populations repeatedly isolated and connected during episodic sea level changes during the Pleistocene epoch, until current day with restricted contemporary gene flow maintaining population genetic structure. Our results show the need for an understanding of both the history and ecology of a species in order to interpret patterns in genetic structure.     

Analysis of microsatellite variation in the spider mite pest Tetranychus turkestani (Acari: Tetranychidae) reveals population genetic structure and raises questions about related ecological factors

The habitat fragmentation that characterizes agricultural systems made up of an array of sympatric crop and weed biotopes might be a major determinant of the population structure of plant‐feeding arthropods. Spider mites are interesting in this regard as several species are highly polyphagous, possibly generating homogenization by plant shifting, but also have the potential of forming host plant races which promotes specialization. This study analyses genetic diversity and structure in natural populations of a spider mite pest, Tetranychus turkestani, collected on both crops and weeds. Five microsatellite markers were used to genotype 283 individuals collected from 15 samples in four locations in southern France. The markers revealed considerable genetic variation, with an average heterozygosity of 0.68. Pairwise Φ_ST estimates calculated between localities showed differentiation in all comparisons. Although geographical distance appears to be a factor that influences T. turkestani population genetic structure at a regional scale, there was no clear evidence for differentiation between mites living on different host plants. A hierarchical analysis of the distribution of the genetic diversity within and between habitats showed that more than 97% of the observed genetic variation accounted for the differentiation between mites collected on the same host plant in a given locality. Significant heterozygote deficiency was found in 11 out of the 15 samples studied. Considering the biology of the mite, a Wahlund effect and inbreeding might explain such an excess of homozygosity. The data support the view that the plants in a given locality are colonized by mites that originate from diverse sources. They also support previous data suggesting that the demographic structure is made up of small demes of inbred individuals. The agricultural‐level implications of the data are discussed, notably the fact that mites may well be capable of moving between host plants, making weeds surrounding the crop fields potential reservoirs for the pest. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 69–78.     

Genetic continuity of brood-parasitic indigobird species

Speciation in brood-parasitic indigobirds (genus Vidua) is a consequence of behavioural imprinting in both males and females. Mimicry of host song by males and host fidelity in female egg laying result in reproductive isolation of indigobirds associated with a given host species. Colonization of new hosts and subsequent speciation require that females occasionally lay eggs in the nests of novel hosts but the same behaviour may lead to hybridization when females parasitize hosts already associated with other indigobird species. Thus, retained ancestral polymorphism and ongoing hybridization are two alternative explanations for the limited genetic differentiation among indigobird species. We tested for genetic continuity of indigobird species using mitochondrial sequences and nuclear microsatellite data. Within West Africa and southern Africa, allopatric populations of the same species are generally more similar to each other than to sympatric populations of different species. Likewise, a larger proportion of genetic variation is explained by differences between species than by differences between locations in alternative hierarchical AMOVAS, suggesting that the rate of hybridization is not high enough to homogenize sympatric populations of different species or prevent genetic differentiation between species. Broad sharing of genetic polymorphisms among species, however, suggests that some indigobird species trace to multiple host colonization events in space and time, each contributing to the formation of a single interbreeding population bound together by songs acquired from the host species.     

Scabies Mites Alter the Skin Microbiome and Promote Growth of Opportunistic Pathogens in a Porcine Model

Background

The resident skin microbiota plays an important role in restricting pathogenic bacteria, thereby protecting the host. Scabies mites (Sarcoptes scabiei) are thought to promote bacterial infections by breaching the skin barrier and excreting molecules that inhibit host innate immune responses. Epidemiological studies in humans confirm increased incidence of impetigo, generally caused by Staphylococcus aureus and Streptococcus pyogenes, secondary to the epidermal infestation with the parasitic mite. It is therefore possible that mite infestation could alter the healthy skin microbiota making way for the opportunistic pathogens. A longitudinal study to test this hypothesis in humans is near impossible due to ethical reasons. In a porcine model we generated scabies infestations closely resembling the disease manifestation in humans and investigated the scabies associated changes in the skin microbiota over the course of a mite infestation.

Methodology/Principal Findings

In a 21 week trial, skin scrapings were collected from pigs infected with S. scabies var. suis and scabies-free control animals. A total of 96 skin scrapings were collected before, during infection and after acaricide treatment, and analyzed by bacterial 16S rDNA tag-encoded FLX-titanium amplicon pyrosequencing. We found significant changes in the epidermal microbiota, in particular a dramatic increase in Staphylococcus correlating with the onset of mite infestation in animals challenged with scabies mites. This increase persisted beyond treatment from mite infection and healing of skin. Furthermore, the staphylococci population shifted from the commensal S. hominis on the healthy skin prior to scabies mite challenge to S. chromogenes, which is increasingly recognized as being pathogenic, coinciding with scabies infection in pigs. In contrast, all animals in the scabies-free cohort remained relatively free of Staphylococcus throughout the trial.

Conclusions/Significance

This is the first experimental in vivo evidence supporting previous assumptions that establishment of pathogens follow scabies infection. Our findings provide an explanation for a biologically important aspect of the disease pathogenesis. The methods developed from this pig trial will serve as a guide to analyze human clinical samples. Studies building on this will offer implications for development of novel intervention strategies against the mites and the secondary infections.     

A Tractable Experimental Model for Study of Human and Animal Scabies

Background

Scabies is a parasitic skin infestation caused by the burrowing mite Sarcoptes scabiei. It is common worldwide and spreads rapidly under crowded conditions, such as those found in socially disadvantaged communities of Indigenous populations and in developing countries. Pruritic scabies lesions facilitate opportunistic bacterial infections, particularly Group A streptococci. Streptococcal infections cause significant sequelae and the increased community streptococcal burden has led to extreme levels of acute rheumatic fever and rheumatic heart disease in Australia''s Indigenous communities. In addition, emerging resistance to currently available therapeutics emphasizes the need to identify potential targets for novel chemotherapeutic and/or immunological intervention. Scabies research has been severely limited by the availability of parasites, and scabies remains a truly neglected infectious disease. We report development of a tractable model for scabies in the pig, Sus domestica.

Methodology/Principal Findings

Over five years and involving ten independent cohorts, we have developed a protocol for continuous passage of Sarcoptes scabiei var. suis. To increase intensity and duration of infestation without generating animal welfare issues we have optimised an immunosuppression regimen utilising daily oral treatment with 0.2mg/kg dexamethasone. Only mild, controlled side effects are observed, and mange infection can be maintained indefinitely providing large mite numbers (>6000 mites/g skin) for molecular-based research on scabies. In pilot experiments we explore whether any adaptation of the mite population is reflected in genetic changes. Phylogenetic analysis was performed comparing sets of genetic data obtained from pig mites collected from naturally infected pigs with data from pig mites collected from the most recent cohort.

Conclusions/Significance

A reliable pig/scabies animal model will facilitate in vivo studies on host immune responses to scabies including the relations to the associated bacterial pathogenesis and more detailed studies of molecular evolution and host adaption. It is a most needed tool for the further investigation of this important and widespread parasitic disease.     

Species status and population genetic structure of grapevine eriophyoid mites

Bud mite, blister mite (Colomerus vitis Pagenstecher), and rust mite (Calepitrimerus vitis Nalepa) (Acari: Eriophyoidae) are recognized grapevine pests. Much of the biology and ecology of these pests is poorly understood. We used two types of molecular markers to gain further insight into the breeding biology and population structure of these mites, using individuals collected from sites around south‐eastern Australia. Patterns of genetic variation observed using PCR‐RFLP of ITS 1 (Internal Transcribed Spacer 1) confirmed the separate species status of the rust mite, and resolved the species status of bud and blister mites, revealing two closely related but distinct species. Microsatellite markers revealed extensive genetic differentiation between bud mite populations and blister mite populations even at micro‐geographical levels, suggesting low movement in these species. The findings indicate that separate control strategies are needed against bud and blister mites, and that localized control strategies are likely to be effective given their limited dispersal.     

The phenomenon of phylogenetic synhospitality in acariform mites (acari: acariformes)--the permanent parasites of vertebrates

The term synhospitality means the association of two or more closely related parasite species with one host species (Eichler, 1966). The cases of two or three synhospitalic species are known from the same host species, and especially ones where parasites were recorded from different parts of the host range, are quite common. The most ordinary reason causing synhospitality in permanent parasites is the host switching. Nevertheless, there are a number of synhospitality cases, where the parasite complex is monophyletic because evolved on a single host species. The special term--"phylogenetic synhospitality" (FS) is proposed for these cases of synhospitality. Most known cases of FS in acariform mites, permanent parasites of vertebrates, are analysed. It is found out that both astigmatan and prostigmatan parasite mites demonstrate a numbers of FS. The majority of these examples represent parasitism of two or three synhospitalic parasite species. Impressive examples of FS involving a number of synhospitalic species is shown by only astigmatan mites inhabiting the fur of mammals or plumage of birds. Most known examples involving four or more mite species are discussed: 51 mite species of the genus Schizocarpus (Chirodiscidae) parasitizing Castor fiber and C. canadensis (Castoridae); 6 species of Listrophorus spp. (Listrophoridae) from Ondatra zibethicus (Cricetidae); 23 species of Listrophoroides s. 1. (Atopomelidae) from Maxomys surifer (Muridae); 21 species of Cytostethum (Atomelidae) from Potorous tridactylus (Potoridae); 4 species of Listrophoroides (Afrolistrophoroides) from Malacomys longipes (Muridae); 7 species of Fainalges (Xolalgidae) from Aratinga holochlora (Psittacidae); 4 species of Zygepigynia (Pteronyssidae) from Chrysocolaptes lucidus (Picidae). The main reason of FS is that, in spite of the Fahrenholz's rule, the speciation of many parasites proceeds much more intensively than in their hosts because of the more rapid replacement of the parasitic generations. The first factor causing FS is the mite speciation it temporary segregated populations of the host (allopatric speciation). In this case, the "multispecies complexes" appeared after the subsequent reintegration of the host populations formerly isolated. The second factor is the speciation due to the specialization of mites to local microhabitats in the fur or plumage of host (sympatric or synxenic speciation). The second way of speciation is most characteristic for mites with highly specialized attaching structures. The phenomenon of FS more resides in ectoparasites of mammals rather than in feather mites in spite of much more structural complicacy of plumage rather than the fur. The high mobility of birds and wide dispersion of their new generations probably embarrass the process of sympatric speciation in their parasites. As a rule, only really significant geographical barriers play role for population isolation in birds. Thus, it could be concluded that two independent factors or their combination lead to FS. (i) The complex and/or disjunctive host range giving a possibility for allopatric speciation in parasites. (ii) The deep mite specialization to local microhabitats on the host body causing sympatric (synxenic) speciation. Fur of mammals and plumage of birds are very complicated in structure and microconditions and provide a considerable number of different microhabitats for mites inhabiting them. The prevalence of one of these two factors depends on the biological peculiarities of both parasites and their hosts. In mites with lesser specialized attaching organs, for example in atopomelids, allopatric speciation dominates. In mites with strongly specialized attaching organs, for example in listrophorids or chirodiscids, both pathways of speciation may take place. In feather mites, sympatric speciation should be more probable due to quite complicate and various structure of feathers in avian hosts. In fur mites, sympatric speciation is more likely in mites parasitizing hosts with peculiar ecology, for example in semiaquatic rodents possessing quite different fur structure in different parts of the body.     

Disentangling hybridization and host colonization in parasitic roundworms of humans and pigs

Knowledge of cross-transmission and hybridization between parasites of humans and reservoir hosts is critical for understanding the evolution of the parasite and for implementing control programmes. There is now a consensus that populations of pig and human Ascaris (roundworms) show significant genetic subdivision. However, it is unclear whether this has resulted from a single or multiple host shift(s). Furthermore, previous molecular data have not been sufficient to determine whether sympatric populations of human and pig Ascaris can exchange genes. To disentangle patterns of host colonization and hybridization, we used 23 microsatellite loci to conduct Bayesian clustering analyses of individual worms collected from pigs and humans. We observed strong differentiation between populations which was primarily driven by geography, with secondary differentiation resulting from host affiliation within locations. This pattern is consistent with multiple host colonization events. However, there is low support for the short internal branches of the dendrograms. In part, the relationships among clusters may result from current hybridization among sympatric human and pig roundworms. Indeed, congruence in three Bayesian methods indicated that 4 and 7% of roundworms sampled from Guatemala and China, respectively, were hybrids. These results indicate that there is contemporary cross-transmission between populations of human and pig Ascaris.     

Host‐specific morphologies but no host races in the commensal bivalve Neaeromya rugifera

Speciation by host shift is one of the explicit models of ecological speciation. A prerequisite of this model is the formation of host races (sympatric populations that show host‐specific genetic structuring and phenotypes). Many members of the diverse marine bivalve superfamily Galeommatoidea have obligate commensal relationships with invertebrate hosts. Some species have the ability to occupy multiple host species, thereby providing potential opportunities to test for the formation of host races. The Northeast Pacific galeommatoidean Neaeromya rugifera attaches to two strikingly different hosts: the blue mud shrimp Upogebia pugettensis and the polychaete sea mouse Aphrodita spp. We tested if this host difference has resulted in the formation of host races using shell morphologies and genetic markers. We found that populations from different hosts differ significantly in shell morphology. However, based on mitochondrial makers, N. rugifera showed no distinct host‐specific genetic structuring, indicating the existence of a panmictic population. We conclude that the host‐specific morphologies these clams exhibit may reflect ecophenotypic plasticity rather than the existence of host races, but this needs to be corroborated with additional genetic data and larger sample sizes. The pronounced conchological variation within N. rugifera calls for further investigation of its taxonomic relationship with its poorly studied, but morphologically similar, sympatric congener Neaeromya compressa.     

Cardinium symbionts cause cytoplasmic incompatibility in spider mites

Intracellular symbiotic bacteria belonging to the Cytophaga-Flavobacterium-Bacteroides lineage have recently been described and are widely distributed in arthropod species. The newly discovered bacteria, named Cardinium sp, cause the expression of various reproductive alterations in their arthropod hosts, including cytoplasmic incompatibility (CI), induction of parthenogenesis and feminization of genetic males. We detected 16S ribosomal DNA sequences similar to those of Cardinium from seven populations of five spider mite species, suggesting a broad distribution of infection of Cardinium in spider mites. To clarify the effect of Cardinium on the reproductive traits of the infected spider mites, infected mites were crossed with uninfected mites for each population. In one of the populations, Eotetranychus suginamensis, CI was induced when infected males were crossed with uninfected females. The other six populations of four species showed no reproductive abnormalities in the F(1) generation, but the possibility of CI effects in the F(2) generation remains to be tested. One species of spider mite, Tetranychus pueraricola, harbored both Cardinium and Wolbachia, but these symbionts seemed to have no effect on the reproduction of the host, even when the host was infected independently with each symbiont.