scholarly journals A Monomorphic Haplotype of Chromosome Ia Is Associated with Widespread Success in Clonal and Nonclonal Populations of Toxoplasma gondii

mBio ◽  
2011 ◽  
Vol 2 (6) ◽  
Author(s):  
Asis Khan ◽  
Natalie Miller ◽  
David S. Roos ◽  
J. P. Dubey ◽  
Daniel Ajzenberg ◽  
...  
Keyword(s):  
Population Structure ◽  
Toxoplasma Gondii ◽  
North America ◽  
South America ◽  
Clonal Expansion ◽  
Content Type ◽  
The North ◽  
Fitness Advantage ◽  
Sexual Recombination ◽  
Geographic Regions

ABSTRACT Toxoplasma gondii is a common parasite of animals that also causes a zoonotic infection in humans. Previous studies have revealed a strongly clonal population structure that is shared between North America and Europe, while South American strains show greater genetic diversity and evidence of sexual recombination. The common inheritance of a monomorphic version of chromosome Ia (referred to as ChrIa*) among three clonal lineages from North America and Europe suggests that inheritance of this chromosome might underlie their recent clonal expansion. To further examine the diversity and distribution of ChrIa, we have analyzed additional strains with greater geographic diversity. Our findings reveal that the same haplotype of ChrIa* is found in the clonal lineages from North America and Europe and in older lineages in South America, where sexual recombination is more common. Although lineages from all three continents harbor the same conserved ChrIa* haplotype, strains from North America and Europe are genetically separate from those in South America, and these respective geographic regions show limited evidence of recent mixing. Genome-wide, array-based profiling of polymorphisms provided evidence for an ancestral flow from particular older southern lineages that gave rise to the clonal lineages now dominant in the north. Collectively, these data indicate that ChrIa* is widespread among nonclonal strains in South America and has more recently been associated with clonal expansion of specific lineages in North America and Europe. These findings have significant implications for the spread of genetic loci influencing transmission and virulence in pathogen populations. IMPORTANCE Understanding parasite population structure is important for evaluating the potential spread of pathogenicity determinants between different geographic regions. Examining the genetic makeup of different isolates of Toxoplasma gondii from around the world revealed that chromosome Ia is highly homogeneous among lineages that predominate on different continents and within genomes that were otherwise quite divergent. This pattern of recent shared ancestry is highly unusual and suggests that some gene(s) found on this chromosome imparts an unusual fitness advantage that has resulted in its recent spread. Although the basis for the conservation of this particularly homogeneous chromosome is unknown, it may have implications for the transmission of infection and spread of human disease.

scholarly journals Genetic diversity of Toxoplasma gondii in animals and humans

2009 ◽  
Vol 364 (1530) ◽  
pp. 2749-2761 ◽  
Author(s):  
L. David Sibley ◽  
Asis Khan ◽  
James W. Ajioka ◽  
Benjamin M. Rosenthal
Keyword(s):  
Population Structure ◽  
Toxoplasma Gondii ◽  
North America ◽  
Companion Animals ◽  
Complex Life Cycle ◽  
South American ◽  
Sexual Recombination ◽  
Severe Infections ◽  
Vertebrate Hosts ◽  
Human Infections

Toxoplasma gondii is one of the most widespread parasites of domestic, wild, and companion animals, and it also commonly infects humans. Toxoplasma gondii has a complex life cycle. Sexual development occurs only in the cat gut, while asexual replication occurs in many vertebrate hosts. These features combine to create an unusual population structure. The vast majority of strains in North America and Europe fall into three recently derived, clonal lineages known as types I, II and III. Recent studies have revealed that South American strains are more genetically diverse and comprise distinct genotypes. These differences have been shaped by infrequent sexual recombination, population sweeps and biogeography. The majority of human infections that have been studied in North America and Europe are caused by type II strains, which are also common in agricultural animals from these regions. In contrast, several diverse genotypes of T. gondii are associated with severe infections in humans in South America. Defining the population structure of T. gondii from new regions has important implications for transmission, immunogenicity and pathogenesis.

scholarly journals A Single Chromosome Unexpectedly Links Highly Divergent Isolates of Toxoplasma gondii

mBio ◽  
2011 ◽  
Vol 3 (1) ◽  
Author(s):  
Katelyn A. Walzer ◽  
Jon P. Boyle
Keyword(s):  
Toxoplasma Gondii ◽  
South America ◽  
North American ◽  
Phylogenetic Analyses ◽  
Unexpected Finding ◽  
Type I ◽  
South American ◽  
Single Chromosome ◽  
Content Type ◽  
The North

ABSTRACT Toxoplasma gondii is an obligate intracellular parasite that can cause disease in all warm-blooded animals studied to date, including humans. Over a billion people have been infected with this parasite worldwide. In Europe and North America, Toxoplasma has a clonal population structure, where only three lineages are highly dominant (strain types I, II, and III). Khan et al. [mBio 2(6): e00228-11, 2011] have carried out phylogenetic analyses on a large number of diverse strains from outside of these lineages and found evidence for a significant split between the clonal North American/European lineages and those in South America. In contrast to most of the genome, nearly all North American/European strains sampled, and the majority of South American strains sampled, harbored at least portions of a monomorphic chromosome Ia (Ia*). In contrast to previous models, these data suggest that the monomorphic haplotype originated in South America and migrated to the North. These authors propose that South American haplotype 12 was a precursor to modern-day type II, while South American haplotypes 6 and 9 crossed with haplotype 12 to give rise to the type I and III lineages, respectively. However, the findings reported by Khan et al. complicate the origin of chromosome Ia, since there are members of haplotypes 9 and 12 with nearly complete versions of Ia* and members of haplotypes 6 and 12 with over 50% of Ia*. This unexpected finding raises exciting new questions about how an entire common chromosome can be found within strains that are highly divergent at most other genomic loci.

scholarly journals Toxoplasma gondii Superinfection and Virulence during Secondary Infection Correlate with the Exact ROP5/ROP18 Allelic Combination

mBio ◽  
2015 ◽  
Vol 6 (2) ◽  
Author(s):  
Kirk D. C. Jensen ◽  
Ana Camejo ◽  
Mariane B. Melo ◽  
Cynthia Cordeiro ◽  
Lindsay Julien ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
North America ◽  
South America ◽  
Secondary Infection ◽  
Congenital Infection ◽  
Immunological Memory ◽  
Type I ◽  
Content Type ◽  
Multiple Exposures ◽  
Parasite Strains

ABSTRACT The intracellular parasite Toxoplasma gondii infects a wide variety of vertebrate species globally. Infection in most hosts causes a lifelong chronic infection and generates immunological memory responses that protect the host against new infections. In regions where the organism is endemic, multiple exposures to T. gondii likely occur with great frequency, yet little is known about the interaction between a chronically infected host and the parasite strains from these areas. A widely used model to explore secondary infection entails challenge of chronically infected or vaccinated mice with the highly virulent type I RH strain. Here, we show that although vaccinated or chronically infected C57BL/6 mice are protected against the type I RH strain, they are not protected against challenge with most strains prevalent in South America or another type I strain, GT1. Genetic and genomic analyses implicated the parasite-secreted rhoptry effectors ROP5 and ROP18, which antagonize the host's gamma interferon-induced immunity-regulated GTPases (IRGs), as primary requirements for virulence during secondary infection. ROP5 and ROP18 promoted parasite superinfection in the brains of challenged survivors. We hypothesize that superinfection may be an important mechanism to generate T. gondii strain diversity, simply because two parasite strains would be present in a single meal consumed by the feline definitive host. Superinfection may drive the genetic diversity of Toxoplasma strains in South America, where most isolates are IRG resistant, compared to North America, where most strains are IRG susceptible and are derived from a few clonal lineages. In summary, ROP5 and ROP18 promote Toxoplasma virulence during reinfection. IMPORTANCE Toxoplasma gondii is a widespread parasite of warm-blooded animals and currently infects one-third of the human population. A long-standing assumption in the field is that prior exposure to this parasite protects the host from subsequent reexposure, due to the generation of protective immunological memory. However, this assumption is based on clinical data and mouse models that analyze infections with strains common to Europe infections with strains common to Europe and North America. In contrast, we found that the majority of strains sampled from around the world, in particular those from South America, were able to kill or reinfect the brains of hosts previously exposed to T. gondii. The T. gondii virulence factors ROP5 and ROP18, which inhibit key host effectors that mediate parasite killing, were required for these phenotypes. We speculate that these results underpin clinical observations that pregnant women previously exposed to Toxoplasma can develop congenital infection upon reexposure to South American strains.

scholarly journals Migration of exotic species of ammonites during highstands of sea level

1992 ◽  
Vol 6 ◽  
pp. 324-324
Author(s):  
Keith Young
Keyword(s):  
North America ◽  
South America ◽  
Exotic Species ◽  
Sea Level ◽  
South Atlantic ◽  
Horn Of Africa ◽  
Mozambique Channel ◽  
The North ◽  
North And South ◽  
Early Late

In northeastern Chihuahua and Trans-Pecos Texas, in the early Late Albian zone of Hysteroceras varicosum occurs the Boeseites romeri (Haas) fauna with B. romeri (Hass), B. perarmata (Hass), B. aff. barbouri (Haas), B. cf. howelli (Haas), B.proteus (Haas), Prohysteroceras cf. P. hanhaense Haas, Elobiceras sp., and Dipoloceras (?) sp. B. perarmata has also been collected at Cerro Mercado, near Monclova, Coahuila. Haas originally described this fauna from Angola. Now, from rocks in the same zone in the Sierra Mojada, Coahuila, Mexico, there is a form related to if not identical with Hysteroceras famelicum Van Hoepen, also originally described from Angola and also from the zone of Hysteroceras varicosum.These fossils are known only from southern North America and Angola; they have not been described from the European Tethys. In 1984 I suggested that during the highstand of sea level of the early Late Albian (Hysteroceras varicosum zone) these ammonites migrated from Angola to Mexico and Trans-Pecos Texas via an epeiric seaway extending across the sag between South America and Africa proposed by Kennedy and Cooper. This would be twelve to fifteen million years prior to an oceanic connection between the North and South Atlantic.I would now ask, can similar epeiric seas and highstands of sea level explain the migration of successive European, Tethyan, Jurassic ammonite faunas down the Mozambique Channel and around the horn of Africa into the Neuquen Basin of Argentina before Africa and Antarctica separated, as proposed by Spath.

Population structure of Heterobasidion annosum from North America and Europe

1993 ◽  
Vol 71 (8) ◽  
pp. 1064-1071 ◽  
Author(s):  
William J. Otrosina ◽  
Thomas E. Chase ◽  
Fields W. Cobb Jr. ◽  
Kari Korhonen
Keyword(s):  
Population Structure ◽  
North America ◽  
North American ◽  
Forest Tree ◽  
Heterobasidion Annosum ◽  
Evolutionary Relationships ◽  
The North ◽  
Isozyme Loci ◽  
Intersterility Groups ◽  
European Populations

Isolates of Heterobasidion annosum (Fr.) Bref. representing North American S and P and European S, P, and F intersterility groups were subjected to isozyme analysis. European S, P, and F groups had more variability than the North American S and P groups in expected hterozygosity, number of alleles per locus, and percent polymorphic loci. In contrast with the North American S and P groups, the European intersterility groups could not be distinguished from each other on the basis of individual isozyme loci, although significant differences in allele frequencies exist between European S and P groups. This suggests that evolution proceeded at different rates in the intersterility groups, or intersterility barriers appeared later in the European populations relative to the North American populations of H. annosum. Changes in climate and host species associations during the Tertiary may have been a major factor in evolution of H. annosum intersterility groups. Key words: allozymes, forest tree hosts, playnological events, evolutionary relationships, Hymenomycetes, root disease.

Speedy Mexico-EU trade deal promises risks and rewards

2017 ◽  
Keyword(s):  
North America ◽  
Free Trade ◽  
North American ◽  
Free Trade Agreement ◽  
Trade Agreement ◽  
Transportation Costs ◽  
Donald Trump ◽  
Content Type ◽  
The North

Subject Mexico-EU trade talks Significance Talks on modernising the Mexico-EU Free Trade Agreement (FTA) have gained urgency since the election of US President Donald Trump as the prospect of an end to free trade within North America forces Mexican officials to get serious about diversifying relations. While negotiators hope to seal a new EU deal by the end of the year, many issues are yet to be addressed and renegotiation of the North American Free Trade Agreement (NAFTA) is absorbing bureaucratic capacity. Impacts Anti-American sentiment stemming from Washington’s hostility could favour European firms and investors in Mexico. The rush to conclude agreements risks bad deals and political blowback from Mexico’s opposition. Transportation costs and connectivity will ultimately matter more for Mexican diversification than already low tariffs.

Ecogeography and the Great American Interchange

Paleobiology ◽  
1991 ◽  
Vol 17 (3) ◽  
pp. 266-280 ◽  
Author(s):  
S. David Webb
Keyword(s):  
North America ◽  
South America ◽  
North American ◽  
Mammalian Fauna ◽  
The South ◽  
Land Bridge ◽  
Southern Mexico ◽  
The North ◽  
Land Mammal ◽  
The Impact

When the isthmian land bridge triggered the Great American Interchange, a large majority of land-mammal families crossed reciprocally between North and South America at about 2.5 Ma (i.e., Late Pliocene). Initially land-mammal dynamics proceeded as predicted by equilibrium theory, with roughly equal reciprocal mingling on both continents. Also as predicted, the impact of the interchange faded in North America after about 1 m.y. In South America, contrary to such predictions, the interchange became decidedly unbalanced: during the Pleistocene, groups of North American origin continued to diversify at exponential rates. Whereas only about 10% of North American genera are derived from southern immigrants, more than half of the modern mammalian fauna of South America, measured at the generic level, stems from northern immigrants. In addition, extinctions more severely decimated interchange taxa in North America, where six families were lost, than in South America, where only two immigrant families became extinct.This paper presents a two-phase ecogeographic model to explain the asymmetrical results of the land-mammal interchange. During the humid interglacial phase, the tropics were dominated by rain forests, and the principal biotic movement was from Amazonia to Central America and southern Mexico. During the more arid glacial phase, savanna habitats extended broadly right through tropical latitudes. Because the source area in the temperate north was six times as large as that in the south, immigrants from the north outnumbered those from the south. One prediction of this hypothesis is that immigrants from the north generally should reach higher latitudes in South America than the opposing contingent of land-mammal taxa in North America. Another prediction is that successful interchange families from the north should experience much of their phylogenetic diversification in low latitudes of North America before the interchange. Insofar as these predictions can be tested, they appear to be upheld.

The North American Chydorus faviformis (Cladocera, Chydoridae) and the honeycombed taxa of other continents

1987 ◽  
Vol 315 (1175) ◽  
pp. 353-402 ◽  
Keyword(s):  
North America ◽  
South America ◽  
Salt Water ◽  
Distinct Species ◽  
Resting Eggs ◽  
The Other ◽  
Careful Study ◽  
Long Distance ◽  
The North ◽  
Species Groups

The taxon Chydorus faviformis , described by Birge from North America in 1893, has been considered to occur also in Asia, Australia, and South America. However, careful study of populations from these regions has revealed that all represent different species, none of which is closely related to C. faviformis . The taxa described here are C. obscurirostris and C. opacus from Australia, C. obscurirostris tasekberae from Malaysia, C. sinensis from China, C.angustirostris from India, and C. parvireticulatus from South America. The taxon in Malaysia differs somewhat from the corresponding taxon in Australia, but cannot be characterized more closely until males and ephippial females become available. The taxa differ among themselves in number of meshes on the shell of parthenogenetic females, surface patterning within the meshes, shape of the rostrum and height of the mesh walls along the edge and near the tip of the rostrum, stoutness and length of the major seta on the inner distal lobe of trunklimb I, shape of the labral plate, and shape and armament of the postabdomen. Ephippial females all have a single resting egg. They differ in the extent of secondary thickenings of the surface network within the shell meshes and in the amount of pigment deposited in the region of the egg locule. Males are most important for separating the taxa, indicating how necessary they are for working out evolutionary similarities and differences. Unfortunately no males of the taxa from Malaysia, India, and South America have been available. For the others, C.faviformis sens. str. is unique in that it is the only taxon in which the male loses its honeycomb (that is, the raised walls of the meshes) on reaching maturity. It also has a sharp pre-anal angle and a marked narrowing of the postabdomen distad from here, which is the pattern typical of species in the Chydorus sphaericus complex. None of the other faviformis -like species share this characteristic. Because of the marked differences in morphology and in geographical distribution of the species in North America and in South America, it is certain that even during the glacial ages, when the northern C. faviformis would have been displaced farthest southward, there was no exchange of either taxon to the other continent. The taxon from Manáos, Brazil listed as C.faviformis in the Birge collection is the C. parvireticulatus reported from much farther south in Brazil and Argentina. In Australia and Asia, except for the uncertain distinctness of the taxon in Malaysia, all the other taxa are markedly separate from each other and hence give no evidence for transfer, as by resting eggs, between continents or even from one region to another on the same continent. All the taxa have been stable in their geographical occurrence for very long periods of time. In addition to the faviformis -like taxa present as distinct species in different regions or on different continents, there are many other species groups of chydorids that have different member species on each continent. One possible explanation of this similarity in gross morphology without any long-distance dispersal of resting eggs to accomplish it is that the various protospecies (corresponding to the species groups) had largely evolved before the original land mass broke up into the present continents and subcontinents. As the distances between the continents increased, the salt-water gaps would come to be impassable barriers to dispersal. Evolution of the isolates would then yield new species, all retaining m any of the features of the protospecies. Each such group from a single protospecies would form the species groups we are now just beginning to recognize.

scholarly journals Sustainability reporting

2017 ◽  
Vol 25 (2) ◽  
pp. 186-215 ◽  
Author(s):  
Kwame Oduro Amoako ◽  
Beverley R. Lord ◽  
Keith Dixon
Keyword(s):  
North America ◽  
South America ◽  
Design Methodology ◽  
Sustainability Reporting ◽  
Social Aspects ◽  
Global Reporting Initiative ◽  
Content Type ◽  
Regional Headquarters ◽  
Sustainability Reports ◽  
Do So

Purpose Sustainability reporting serves as a means of communication between corporations and their stakeholders on sustainability issues. This study aims to identify and account for the contents of sustainability reporting communicated through the websites of the plants in five continents of the same multinational mining corporation. Design/methodology/approach This study uses data published by Newmont Mining Corporation. The corporation has regional headquarters in five continents: Africa, Asia, Australia and North America and South America. The data were drawn from the websites of the five plants adjacent to those regional headquarters. Economic, environmental and social aspects of sustainability as reported by each plant were identified; to do so, a disclosure analysis based on the elements of the Global Reporting Initiative and the United Nations Division for Sustainability Development was used. These aspects were then compared and contrasted to highlight if, and to what extent, institutional isomorphism influences variations in sustainability disclosures among plants compared with the parent company. Findings It was found that most of the reporting about sustainability matters comprises narratives; there were also a few physical measures but very little financial information. Notwithstanding that the websites of all five plants used similar headings, the contents of reports differed. The reports from the plants in Australia, South America and Africa were more comprehensive than those from the plants in Asia and North America. The authors attribute these differences to institutionalisation of location-specific characteristics, including management discretion, legislation and societal pressures influencing sustainability reporting. The authors argue that managers responsible for preparing sustainability reports and who work essentially as sustainability accountants should develop templates and measures to raise the standard and comprehensiveness of reports for improved communication, information and behaviour. Originality/value Extant studies on sustainability reporting have focused mainly on comparisons between sustainability reports published by different corporations or sustainability reports published in different years by the same corporation. The authors believe that this is one of the first studies to have examined differences in sustainability information published by different subsidiaries within the same large corporation and the first to show how concurrent disclosures can differ.

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