Amblyospora trinus N. sp. (Microsporida: Amblyosporidae) in the Australian mosquito Culex halifaxi (Diptera: Culicidae)

Amblyospora khaliulini (Microsporidia: Amblyosporidae): Investigations on its life cycle and ecology in Aedes communis (Diptera: Culicidae) and Acanthocyclops vernalis (Copepoda: Cyclopidae) with redescription of the species

A multi-year study was conducted to examine the natural ecology of the microsporidium Amblyospora khaliulini and more fully characterize parasite development and histopathology in all stages of its primary mosquito host, Aedes communis and intermediate copepod host, Acanthocyclops vernalis with redescription of the species. A. khaliulini exhibits polymorphic development, produces three morphologically and functionally distinct spores, and is both horizontally and vertically transmitted. Development in A. vernalis is restricted to females, occurs within the ovaries and results in death of the host. Development is haplophasic with division by binary and multiple fission producing rosette-shaped sporogonial plasmodia and conical uninucleate spores that are orally infectious to Ae. communis larvae. Both sexes are equally susceptible and infections are confined to testes in males and ovaries in females. Initial stages of development include uninucleate schizonts that undergo karyokinesis forming diplokaryotic meronts that divide repeatedly by binary fission. Sporogony occurs in both host sexes, but sporogenesis does not progress normally in adult males and elliptical, thin walled binucleate spores that function in vertical transmission of the microsporidium via infection of the ovaries and eggs are formed in adult females only. Development of vertically acquired infections in larval Ae. communis hosts occurs within fat body tissue, leads to the production of meiospores in male hosts only and results in death during the 4th larval stadium. Initial development is characterized by merogonial multiplication of diplokarya by synchronous binary division producing additional diplokarya. The cessation of merogony and the onset of sporogony are characterized by the simultaneous secretion of a sporophorous vesicle and meiotic division of diplokarya resulting in the formation of octonucleate sporonts that undergo cytokinesis and sporogenesis to form eight uninucleate, broadly ovoid meiospores enclosed within a sporophorous vesicle. The natural prevalence of patent vertically acquired fat body infections in field populations of Ae. communis ranged from 1.6% to 3.6%. Yearly infection rates in A. vernalis copepods ranged from 57.1% to 15.0%. Prevalence rates of horizontally acquired infections in emerging adult Ae. communis ranged from 69.0% to 11.9% in males and 50.0% to 16.4% in females.

Morphological and molecular characterization of a microsporidian parasite, Takaokaspora nipponicus n. gen., n. sp. from the invasive rock pool mosquito, Ochlerotatus japonicus japonicus

A new genus and species of Microsporidia, Takaokaspora nipponicus n. gen., n. sp. is described from Ochlerotatus japonicus japonicus (Theobald) and Ochlerotatus hatorii (Yamada) based on light microscope and ultrastructural morphology, developmental features, transmission cycles and comparative sequence analyses of the small subunit ribosomal DNA (SSU rDNA). The microsporidium is both vertically and horizontally transmitted, exhibits dimorphic development alternating between diplokaryotic and monokaryotic stages and produces two morphologically distinct spores, one in larvae and another in adult females. Horizontal transmission of infection to larval mosquitoes occurs via direct oral ingestion of uninucleate spores that are produced in vertically-infected larval hosts. Development in horizontally-infected hosts is diplokaryotic following karyokinesis of uninucleate schizonts and binary fission to produce small (4.3μm × 2.0μm) membrane free, ovoid, binucleate spores that are confined to adult female reproductive tissues (ovariole sheath and oviducts). Vertical transmission of the microsporidium from adult females to larval progeny takes place via surface contamination of the egg (transovum). Microsporidian development in vertically-infected larvae is haplophasic with unpaired nuclei throughout, producing rosette-shaped sporogonial plasmodia contained within a thin non-persistent sporophorous vesicle and culminating in the formation of membrane free, uninucleate, conical spores (7.0μm×2.8μm). Development is confined to host fat body tissue which appears as swollen white masses in the thorax and selected segments of the abdomen causing larvae to appear abnormally distorted and results in death during the third and fourth instar stages. The SSU rDNA sequences obtained from the two morphologically identical microsporidia isolated from Oc. j. japonicus and Oc. hatorii were nearly identical and unique when compared with GenBank entries of all other mosquito-parasitic species. Phylogenetic trees constructed by Maximum Parsimony, Maximum Likelihood and bootstrap analyses using the Neighbor Joining search parameter yielded similar typologies. In each case, the novel microsporidium was the sister group to the clade containing Parathelohania species from Anopheles mosquitoes and the monotypic Novothelohania ovalae from Ochlerotatus caspius showing approximately 10-13% sequence divergence to those two genera providing strong support for establishment as a separate genus.

Ultrastructural characterization and comparative phylogenetic analysis of new microsporidia from Siberian mosquitoes: evidence for coevolution and host switching

A survey of mosquito larvae infected with microsporidia was conducted from 2005 to 2008 in the Tomsk, Kemerovo and Novosibirsk regions of western Siberia, Russia. Twenty-one morphologically and genetically unique species of microsporidia were isolated from nine species of Anopheles, Aedes, Culex and Ochlerotatus mosquitoes including: (1) 14 proposed new species of Amblyospora (A. bakcharia, A. baritia, A. bogashovia, A. chulymia, A. hristinia, A. jurginia, A. kazankia, A. mavlukevia, A. mocrushinia, A. modestium, A. salairia, A. severinia, A. shegaria, and A. timirasia); (2) a newly proposed genus and species, Novothelohaniaovalae and; (3) six species of Amblyospora (A. flavescens, A. kolarovi, A. rugosa), Parathelohania (P. divulgata and P. tomski) and Trichoctosporea (T. pygopellita) from which gene sequences had not been previously obtained. Detailed ultrastructure of meiospores revealed unique cytological features associated with the length, arrangement and ratio of broad to narrow coils of the polar filament, comparative thickness of the exospore and endospore, and overall size of each species reaffirming their value in distinguishing taxonomic relationships. SSU rDNA sequences obtained from each species of microsporidia were unique when compared with GenBank entries. Phylogenetic trees constructed by Maximum Parsimony, Maximum Likelihood and Neighbor Joining analyses yielded similar topologies with a high degree of congruence between parasite and host at the generic level. Species that parasitize Aedes/Ochlerotatus and Culex mosquitoes segregate into distinct monophyletic groupings mirroring their host phylogeny, while species from Anopheles mosquitoes group as a sister clade basal to the entire group of mosquito-parasitic microsporidia as their Anopheles hosts cluster as a sister clade to the entire group of culicine mosquitoes. This provides strong evidence for host-parasite coevolution by descent at the generic level and limited host lineage switching between unrelated taxa. Among parasites of Aedes/Ochlerotatus and Anopheles mosquitoes, we found several instances where a single mosquito species serves as a host for two or more related species of microsporidia, an observation consistent with host switching and independent parasite speciation. Among the microsporidian parasites of Culex mosquitoes, we found only one parasite per host indicating a higher degree of host specificity and less host switching among parasites of this genus. Findings suggest a degree of host-parasite co-speciation with host switching occurring occasionally when the "normal" host is unavailable in the aquatic ecosystem. Frequency of host switching seems to be occurring in proportion to host relatedness and does not cross generic boundaries in this system.

Virulence and transmission modes of two microsporidia inDaphnia magna

To understand the relationship between mode of transmission and virulence, we investigated 2 microsporidian parasites inDaphnia magnalaboratory populations.Pleistophora intestinalisis only transmitted horizontally, whileTuzetiasp. is transmitted vertically with high efficiency from mothers to parthenogenetic male and female offspring. We were not able to transmitTuzetiahorizontally in the laboratory.Tuzetiareduces host life-time reproductive success and host survival to a much greater extent than doesP. intestinalis.Tuzetia-infected hosts were rapidly outcompeted by uninfected hosts. We suspect thatTuzetiainfections may persist in natural populations by an as yet undiscovered horizontal transmission. It is possible that an alternate host species may be involved. We present a mathematical model to analyse the conditions for the persistence of a parasite with perfect vertical and an additional degree of horizontal transmission. We show that horizontal and vertical transmission contribute additively to a parasite's ability to invade and persist. Since the fitness contribution of horizontal transmission increases with population size, only very low transmission probabilities per host-to-host contact are necessary for the persistence of parasites occurring in large populations such as those commonly found forDaphnia. The detection of such low rates of horizontal transmission appears unlikely under laboratory conditions since the necessary number of host-to-host (or host-to-spore) contacts is not feasible. We review mechanisms that can maintain vertically transmitted parasites in nature.

Vavraia lutzomyiae n. sp. (Phylum Microspora) infecting the sandfly Lutzomyia longipalpis (Psychodidae, Phlebotominae), a vector of human visceral leishmaniasis

Vavraia lutzomyiae (Microsporida; Pleistophoridae) is a new species parasitic in the tropical phlebotomine sandfly, Lutzomyia longipalpis (Diptera, Psychodidae, Phlebotominae), a major vector of Leishmania chagasi in Latin America where human visceral leishmaniasis is endemic. Infected larvae and pupae were parasitized in the abdomen, and some adults were parasitized in Malpighian tubules and midgut. The sporogonial plasmodium divided by multiple divisions into up to 64 uninucleate sporoblasts. These stages were surrounded outside the plasmalemma by a thick, amorphous dense coat and transformed into a merontogenetic sporophorous vesicle within which the sporonts developed into sporoblasts. The mature microsporidian spores were broadly ellipsoidal and measured 6.1+/-0.43 x 3.1+/-0.15 microm. The spore wall consisted of a transparent endospore (approximately 100 nm) and a thin electron dense exospore (approximately 30 nm) with the outer limit slightly undulated. Spores contained a polar filament arranged peripherally in a single layer of eight to nine wide anterior coils (approximately 125 nm diameter), and three to four narrow posterior coils (approximately 70 nm diameter). Transverse sections revealed a concentric layer organization with the internal layer surrounded by numerous (up to 25) longitudinal microfibrils. The angle of tilt of the polar filament was about 65-68 degrees.

Molecular Phytogeny and Evolution of Mosquito Parasitic Microsporidia (Microsporidia: Amblyosporidae)1

Amblyospora species and other aquatic Microsporidia were isolated from mosquitoes, black flies, and copepods and the small subunit ribosomal RNA gene was sequenced. Comparative phylogenetic analysis showed a correspondence between the mosquito host genera and their Amblyspora parasite species. There is a clade of Amblyospora species that infect the Culex host group and a clade of Amblyospora that infect the Aedes/Ochlerotatus group of mosquitoes. Parathelohania species, which infect Anopheles mosquitoes, may be the sister group to the Amblyospora in the same way that the Anopheles mosquitoes are thought to be the sister group to the Culex and Aedes mosquitoes. In addition, by sequence analysis of small subunit rDNA from spores, we identified the alternate copepod host for four species of Amblyospora. Amblyospora species are specific for their primary (mosquito) host and each of these mosquito species serves as host for only one Amblyospora species. On the other hand, a single species of copepod can serve as an intermediate host to several Amblyospora species and some Amblyospora species may be found in more than one copepod host. Intrapredatorus barri, a species within a monotypic genus with Amblyospora-like characteristics, falls well within the Amblyospora clade. The genera Edhazardia and Culicospora, which do not have functional meiospores and do not require an intermediate host, but which do have a lanceolate spore type which is ultrastructurally very similar to the Amblyospora spore type found in the copepod, cluster among the Amblyospora species. In the future, the genus Amblyospora may be redefined to include species without obligate intermediate hosts. Hazardia, Berwaldia, Larssonia, Trichotuzetia, and Gurleya are members of a sister group to the Amblyospora clades infecting mosquitoes, and may be representatives of a large group of aquatic parasites.

Life cycle, ultrastructure and molecular phylogeny of Hyalinocysta chapmani (Microsporidia: Thelohaniidae), a parasite of Culiseta melanura (Diptera: Culicidae) and Orthocyclops modestus (Copepoda: Cyclopidae)

The complete life cycle of the microsporidium Hyalinocysta chapmani is described from the primary mosquito host Culiseta melanura and the intermediate copepod host Orthocyclops modestus. Infections are initiated in larval C. melanura following the oral ingestion of uninucleate spores from infected copepods. Spores germinate within the lumen of the midgut and directly invade fat body tissue where all development occurs. Uninucleated schizonts undergo binary division (schizogony) followed by karyokinesis (nuclear division) to form diplokaryotic meronts. Merogony is by synchronous binary division. The onset of sporogony is characterized by the simultaneous secretion of a sporophorous vesicle and meiotic division of the diplokaryon resulting in the formation of eight ovoid meiospores enclosed within a sporophorous vesicle. Most infected larvae die during the fourth stadium and there is no evidence of a developmental sequence leading to vertical transmission. Hyalinocysta chapmani is horizontally transmitted to O. modestus via oral ingestion of meiospores. Infections become established within ovarian tissue of females and all parasite development is haplophasic. Uninucleate schizonts divide by binary division during an initial schizogonic cycle. Newly formed uninucleate cells produce a thin sporophorous vesicle and undergo repeated nuclear division during sporogony to produce a rosette-shaped, multinucleated sporogonial plasmodium with up to 18 nuclei. This is followed by cytoplasmic cleavage, sporogenesis, and disintegration of the sporophorous vesicle to form membrane-free uninucleate spores. Infected females eventually die and there is no egg development. The small subunit rDNA sequence of H. chapmani isolated from meiospores from C. melanura was identical to the small subunit rDNA sequence obtained from spores from O. modestus, corroborating the laboratory transmission studies and confirming the intermediary role of O. modestus in the life cycle. Phylogenetic analysis was conducted with closely related microsporidia from mosquitoes. Hyalinocysta chapmani did not cluster within described Amblyospora species and can be considered a sister group, warranting separate genus status.

rDNA phylogeny of Intrapredatorus barri (Microsporida: Amblyosporidae) parasitic to Culex fuscanus Wiedemann (Diptera: Culicidae)

Intrapredatorus barri, a microsporidian parasite of the predator mosquito Culex fuscanus Wiedemann has been shown to be heterosporous. In many features this species has been reported to be similar to Amblyospora trinus, another microsporidian parasite of a different predator mosquito which was thus proposed for reassignation to the genus Intrapredatorus. In this report small subunit rDNA has been sequenced from I. barri and phylogenetic analysis of 42 microsporidia sequences has been performed. The molecular data show that I. barri can not be a member of the genus Amblyospora. Furthermore, the phylogenetic analysis shows, with high confidence, that the Amblyospora spp. sequences in the present study are not monophyletic.

Phylogeny of amblyospora (Microsporida: amblyosporidae) and related genera based on small subunit ribosomal DNA data: A possible example of host parasite cospeciation

Small subunit ribosomal RNA (SSU rRNA) gene sequences were analyzed for six species and four genera of microsporidia from mosquito hosts; Amblyospora stimuli (Aedes stimulans), Amblyospora californica (Culex tarsalis), Amblyospora sp. (Culex salinarius), Edhazardia aedis (Aedes aegypti), Culicosporella lunata (Culex pilosus), and Parathelohania anophelis (Anopheles quadrimaculatus). Comparison of these sequences to those of other microsporidia show that these sequences are longer with the SSU rRNA gene of E. aedis being the longest microsporidia sequenced to date (1447 base pairs). Parsimony, maximum likelihood, and distance methods produced identical trees, suggesting that the above microsporidian taxa, contrary to current classification schemes, form a monophyletic group. Relationships within this group are further supported by high bootstrap and decay analysis values. Based on the molecular analysis, P. anophelis is the most divergent species in this group of mosquito parasites. Amblyospora is paraphyletic with A. californica and Amblyospora sp., forming a sister taxon to a clade composed of E. aedis and A. stimuli. Culicosporella lunata comprises a sister taxon to the Amblyospora/Edhazardia clade. The pattern of host relationships on the tree provides preliminary evidence that the branching pattern seen here may indicate that host-parasite cospeciation is an important mechanism of evolution in this group.

A microsporidium of the predacious mosquito culex fuscanus wiedemann (Diptera: culicidae) from southern taiwan

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A proposal for typical eukaryotic meiosis in microsporidians

A review of key publications concerning the biology and life cycles of microsporidians has led us to challenge recent proposals that they exhibit a unique process of meiosis when compared with other eukaryotes. The basic data used to support this challenge are the same as those used by researchers suggesting atypical meiosis, but the data are analyzed from a different viewpoint. Arguments are put forward to support a testable hypothesis that meiosis in microsporidians is identical to that which occurs in other eukaryotes. It is proposed that confusion resulted because two separate cytological developmental sequences for diplokaryotic meronts in mosquito fat body cells were previously interpreted as a single sequence. By rearrangement of the original data into two developmental sequences, one abortive and the other for typical meiosis, a better fit was obtained between cytological stages and microphotometric measurements of nuclear DNA content. This improved data fit and the existence of similar nuclear developmental sequences in the fungi are used to support our hypothesis.Key words: microsporidia, meiosis, eukaryotes.