Wolbachia host shifts: routes,mechanisms, constraints and evolutionary consequences

Wolbachia is one of the most abundant endosymbionts on earth, with a wide distribution especially in arthropods. Effective maternal transmission and the induction of various phenotypes in their hosts are two key features of this bacterium. Here, we review our current understanding of another central aspect of Wolbachia's success: their ability to switch from one host species to another. We build on the proposal that Wolbachia host shifts occur in four main steps: (i) physical transfer to a new species; (ii) proliferation within that host; (iii) successful maternal transmission; and (iv) spread within the host species. Host shift can fail at each of these steps, and the likelihood of ultimate success is influenced by many factors. Some stem from traits of Wolbachia (different strains have different abilities for host switching), others on host features such as genetic resemblance (e.g. host shifting is likely to be easier between closely related species), ecological connections (the donor and recipient host need to interact), or the resident microbiota. Host shifts have enabled Wolbachia to reach its enormous current incidence and global distribution among arthropods in an epidemiological process shaped by loss and acquisition events across host species. The ability of Wolbachia to transfer between species also forms the basis of ongoing endeavours to control pests and disease vectors, following artificial introduction into uninfected hosts such as mosquitoes. Throughout, we emphasise the many knowledge gaps in our understanding of Wolbachia host shifts, and question the effectiveness of current methodology to detect these events. We conclude by discussing an apparent paradox: how can Wolbachia maintain its ability to undergo host shifts given that its biology seems dominated by vertical transmission?     

The diversity,recombination and horizontal transmission of Wolbachia in spiders in China

Wolbachia are maternally inherited endosymbiotic bacteria. These intracellular bacteria are common in arthropods and could manipulate host reproduction in diverse ways, such as feminization, parthenogenesis, male killing and cytoplasmic incompatibility. In spiders, infection by Wolbachia has been found in a total of 99 species belonging to 62 genera and 17 families. Furthermore, recent studies analyzed the phylogeny of Wolbachia in Hylyphantes graminicola, 2 cave spiders and Agelenopsis species using multilocus sequence typing (MLST) approach. However, the diversity of Wolbachia strains determined by MLST in spiders from China is still largely unknown.In this study, we collected 1153 spider individuals from Mangshan in China and screened for Wolbachia in 975 individuals representing 68 spider species belonging to 45 genera of 16 families. We analyzed the phylogenetic relationship between Wolbachia and their host spiders by MLST approach. We found novel infections of Wolbachia in 1 family, 9 genera and 20 species of spiders. We found 13 new Wolbachia strains and suggest that group A is more common than group B in Wolbachia that infect spiders. Our results revealed three recombination events of the concatenated multilocus sequences in Wolbachia that infect spiders. Furthermore, our results demonstrated the phylogenetic incongruence between Wolbachia and spiders, suggesting the horizontal transmission of Wolbachia in spiders.We suggest that recombination and horizontal transmission may play an important role in the diversity and evolution of Wolbachia in spiders.     

Exploring human-animal host interactions and emergence of COVID-19: Evolutionary and ecological dynamics

The novel coronavirus disease (COVID-19) that emerged in December 2019 had caused substantial morbidity and mortality at the global level within few months. It affected economies, stopped travel, and isolated individuals and populations around the world. Wildlife, especially bats, serve as reservoirs of coronaviruses from which the variant Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) emerged that causes COVID-19. In this review, we describe the current knowledge on COVID-19 and the significance of wildlife hosts in its emergence. Mammalian and avian coronaviruses have diverse host ranges with distinct lineages of coronaviruses. Recombination and reassortments occur more frequently in mixed-animal markets where diverse viral genotypes intermingle. Human coronaviruses have evolved through gene gains and losses primarily in interfaces where wildlife and humans come in frequent contact. There is a gap in our understanding of bats as reservoirs of coronaviruses and there is a misconception that bats periodically transmit coronaviruses to humans. Future research should investigate bat viral diversity and loads at interfaces between humans and bats. Furthermore, there is an urgent need to evaluate viral strains circulating in mixed animal markets, where the coronaviruses circulated before becoming adapted to humans. We propose and discuss a management intervention plan for COVID-19 and raise questions on the suitability of current containment plans. We anticipate that more virulent coronaviruses could emerge unless proper measures are taken to limit interactions between diverse wildlife and humans in wild animal markets.     

A moderate level of hypovirulence conferred by a hypovirus in the avocado white root rot fungus,Rosellinia necatrix

Two isolates of Rosellinia necatrix (Rn118-8 and Rn480) have previously obtained from diseased avocado trees in commercial orchards of the coastal area in southern Spain. Rn118-8 and Rn480 have weak virulence on avocado plants, and are infected by R. necatrix hypovirus 2 (RnHV2). In this work, the possible biological effects of the hypovirus on R. necatrix were tested. First, RnHV2 was transmitted from each of Rn118-8 and Rn480 to a highly virulent, RnHV2-free isolate of R. necatrix (Rn400) through hyphal anastomosis, using zinc compounds which attenuate the mycelial incompatibility reactions and allow for horizontal virus transfer between vegetatively incompatible fungal strains. Next, we carried out an analysis of growth rate in vitro and a virulence test of these newly infected strains in avocado plants. We obtained five strains of Rn400 infected by RnHV2 after horizontal transmission, and showed some of them to have lower colony growth in vitro and lower virulence on avocado plants compared with virus-free Rn400. These results suggest that R. necatrix isolates infected by RnHV2 could be used as novel virocontrol agents to combat avocado white root rot.     

ROI-Based Compression Strategy of 3D MRI Brain Datasets for Wireless Communications

ObjectivesBecause of the large amount of medical imaging data, the transmission process becomes complicated in telemedicine applications. Thus, in order to adapt the data bit streams to the constraints related to the limitation of the bandwidths a reduction of the size of the data by compression of the images is essential. Despite the improvements in the field of compression, the transmission itself can also introduce errors. For this reason, it is important to develop an adequate strategy which will help reduce this volume of data without having to introduce some distortion and resist the errors introduced by the channel noise during transmission. Thus, in this paper, we propose a ROI-based coding strategy and unequal bit stream protection to meet this dual constraint.Material and methodsThe proposed ROI-based compression strategy with unequal bit stream protection is composed of three parts: the first one allows the extraction of the ROI region, the second one consists of a ROI-based coding and the third one allows an unequal protection of the ROI bit stream.First, the Regions Of Interest (ROI) are extracted by hierarchical segmentation of these regions according to a segmentation method based on the technique of Marker-based-watershed combined with the technique of active contours by level set. The resulting regions are selectively encoded by a 3D coder based on a shape adaptive discrete wavelet transform 3D-BISK, where the compression ratio of each region depends on its relevance in diagnosis. These obtained regions of interest are protected with an error-correcting code of Reed-Solomon type with a code rate that varies according to the relevance of the region by an unequal protection strategy (UEP).ResultsThe performance of the proposed compression scheme is evaluated in several ways. First, tests are performed to study the impact of errors on the different bit streams. In the first place, these tests are carried out in order to study the effect of the variation of the compression rates on the different bit streams. Secondly, different Reed Solomon error-correcting codes of different code rates are tested at different compression rates on a BSC channel. Finally, the performances of this coding strategy are compared with those of SPIHT 3D in the case of transmission on a BSC channel.ConclusionThe obtained results show that the proposed method is quite efficient in transmission time reduction. Therefore, our proposed scheme will reduce the volume of data without having to introduce some distortion and resist the errors introduced by the channel noise in the case of telemedicine.     

Trophic divergence of Lake Kivu cichlid fishes along a pelagic versus littoral habitat axis

Local adaptation to the littoral and pelagic zones in two cichlid haplochromine fish species from Lake Kivu was investigated using morphometrics. Cranial variation and inferred jaw mechanics in both sexes of the two species across the two habitat types were quantified and compared. Comparisons of littoral versus pelagic populations revealed habitat‐specific differences in the shape of the feeding apparatus. Also, kinematic transmission of the anterior jaw four‐bar linkage that promotes greater jaw protrusion was higher in the pelagic zone than in the littoral zone for both species. Inferred bite force was likewise higher in pelagic zone fish. There were also sex‐specific differences in craniofacial morphology as males exhibited longer heads than females in both habitats. As has been described for other cichlids in the East African Great Lakes, local adaptation to trophic resources in the littoral and pelagic habitats characterizes these two Lake Kivu cichlids. Similar studies involving other types of the Lake Kivu fishes are recommended to test the evidence of the observed trophic patterns and their genetic basis of divergences.     

The Effect of Xanthine/Xanthine Oxidase Generated Reactive Oxygen Species on Synaptic Transmission

The effect of reactive oxygen species generated by the interaction of xanthine and xanthine oxidase on synaptic transmission was examined at the squid giant synapse and the lobster neuromuscular junction. Exposure of these synaptic regions to xanthine/xanthine oxidase produced a significant depression in evoked release, with no change in either resting membrane properties or in the action potential. Addition of catalase to the xanthine/xanthine oxidase-containing media partially blocked the synaptic depression, indicating that H₂ O ₂ contributes to the synaptic changes induced by exposure to xanthine/xanthine oxidase. H₂ O ₂ applied directly to the perfusing media also produced a decrease in synaptic efficacy. The results demonstrate that reactive oxygen species, in general, depress evoked synaptic transmission.     

Influence of the forest caterpillar hunter Calosoma sycophanta on the transmission of microsporidia in larvae of the gypsy moth Lymantria dispar

• 1 The behaviour of predators can be an important factor in the transmission success of an insect pathogen. We studied how Calosoma sycophanta influences the interaction between its prey [Lymantria dispar (L.) (Lepidoptera, Lymantriidae)] and two microsporidian pathogens [Nosema lymantriae (Microsporidia, Nosematidae) and Vairimorpha disparis (Microsporidia, Burellenidae)] infecting the prey.
• 2 Using laboratory experiments, C. sycophanta was allowed to forage on infected and uninfected L. dispar larvae and to disseminate microsporidian spores when preying or afterwards with faeces.
• 3 The beetle disseminated spores of N. lymantriae and V. disparis when preying upon infected larvae, as well as after feeding on such prey. Between 45% and 69% of test larvae became infected when C. sycophanta was allowed to disseminate spores of either microsporidium.
• 4 Laboratory choice experiments showed that C. sycophanta did not discriminate between Nosema‐infected and uninfected gypsy moth larvae. Calosoma sycophanta preferred Vairimorpha‐infected over uninfected gypsy moth larvae and significantly influenced transmission.
• 5 When C. sycophanta was allowed to forage during the latent period on infected and uninfected larvae reared together on caged, potted oak saplings, the percentage of V. disparis infection among test larvae increased by more than 70%. The transmission of N. lymantriae was not affected significantly in these experiments.
• 6 Beetles never became infected with either microsporidian species after feeding on infected prey.
• 7 We conclude that the transmission of N. lymantriae is not affected. Because no V. disparis spores are released from living larvae, feeding on infected larvae might enhance transmission by reducing the time to death and therefore the latent period.

     

Disease phenotype in sheep after infection with cloned murine scrapie strains

Prion diseases exhibit different disease phenotypes in their natural hosts and when transmitted to rodents, and this variability is regarded as indicative of prion strain diversity. Phenotypic characterization of scrapie strains in sheep can be attempted by histological, immunohistochemical and biochemical approaches, but it is widely considered that strain confirmation and characterization requires rodent bioassay. Examples of scrapie strains obtained from original sheep isolates by serial passage in mice include ME7, 79A, 22A and 87V. In order to address aspects of prion strain stability across the species barrier, we transmitted the above murine strains to sheep of different breeds and susceptible Prnp genotypes. The experiment included 40 sheep dosed by the oral route alone and 36 sheep challenged by combined subcutaneous and intracerebral routes. Overall, the combined route produced higher attack rates (~100%) than the oral route (~50%) and 2–4 times shorter incubation periods. Uniquely, 87V given orally was unable to infect any sheep. Overall, scrapie strains adapted and cloned in mice produce distinct but variable disease phenotypes in sheep depending on breed or Prnp genotype. Further re-isolation experiments in mice are in progress in order to determine whether the original cloned murine disease phenotype will reemerge.