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      Extraordinary Trypanosoma cruzi diversity within single mammalian reservoir hosts implies a mechanism of diversifying selection

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          Abstract

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          Research highlights

          ► We report extraordinary genetic diversity within single reservoir hosts of Trypanosoma cruzi. ► Two hundred and thirty-three biological clones were taken from eight mammals. ► Nine polymorphic microsatellite markers were amplified. ► Forty-nine distinct multilocus genotypes were defined. ► Widespread multiclonality contrasts with the precarious nature of T. cruzi vectorial transmission. ► We propose that non-neutral processes could account for the diversity observed.

          Abstract

          Trypanosoma cruzi is an evolutionarily ancient parasitic protozoan endemic to the Americas. Multiple genetic and phenotypic markers indicate that this parasite is highly diverse, with several divergent and discrete major genotypes reported. Infection multiclonality has been observed among numerous metazoan and unicellular endoparasitic species. However, few studies report the complexity of mixed infections within an individual host in any detail or consider their ecological and biological implications. Here we report extraordinary genetic diversity within single reservoir hosts of T. cruzi I using nine polymorphic microsatellite markers across 211 clones from eight mammals from three different sylvatic foci in South America. Forty-nine distinct multilocus genotypes were defined, with as many as 10 isolated from the same host. We discuss our data in the light of previous population genetic studies of this and related parasitic protozoa and contrast high levels of diversity within each host with the precarious nature of T. cruzi contaminative vectorial transmission. Finally, we propose that non-neutral processes could easily account for the diversity we observe and suggest a functional link with survival in the host.

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          Most cited references 34

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          Arlequin (version 3.0): An integrated software package for population genetics data analysis

          Arlequin ver 3.0 is a software package integrating several basic and advanced methods for population genetics data analysis, like the computation of standard genetic diversity indices, the estimation of allele and haplotype frequencies, tests of departure from linkage equilibrium, departure from selective neutrality and demographic equilibrium, estimation or parameters from past population expansions, and thorough analyses of population subdivision under the AMOVA framework. Arlequin 3 introduces a completely new graphical interface written in C++, a more robust semantic analysis of input files, and two new methods: a Bayesian estimation of gametic phase from multi-locus genotypes, and an estimation of the parameters of an instantaneous spatial expansion from DNA sequence polymorphism. Arlequin can handle several data types like DNA sequences, microsatellite data, or standard multi-locus genotypes. A Windows version of the software is freely available on http://cmpg.unibe.ch/software/arlequin3.
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            Tackling the population genetics of clonal and partially clonal organisms.

            Many clonal organisms experience occasional events of sexual recombination, with profound consequences for their population dynamics and evolutionary trajectories. With the recent development of polymorphic genetic markers and new statistical methods, we now have an unprecedented ability to detect recombination in organisms that are thought to reproduce strictly, or essentially asexually. However, it is not always obvious which methodology to apply. Consequently, biologists might decide how to analyse their data without clear guidelines. Here, we discuss the available methods, focusing on those best suited when working with limited genetic information, such as a few genetic markers or DNA sequences. We conclude by commenting on the prospects offered by some recent conceptual advances and the access to high throughput technologies in an increasing number of model organisms.
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              Mechanism of genetic exchange in American trypanosomes.

              The kinetoplastid Protozoa are responsible for devastating diseases. In the Americas, Trypanosoma cruzi is the agent of Chagas' disease--a widespread disease transmissible from animals to humans (zoonosis)--which is transmitted by exposure to infected faeces of blood-sucking triatomine bugs. The presence of genetic exchange in T. cruzi and in Leishmania is much debated. Here, by producing hybrid clones, we show that T. cruzi has an extant capacity for genetic exchange. The mechanism is unusual and distinct from that proposed for the African trypanosome, Trypanosoma brucei. Two biological clones of T. cruzi were transfected to carry different drug-resistance markers, and were passaged together through the entire life cycle. Six double-drug-resistant progeny clones, recovered from the mammalian stage of the life cycle, show fusion of parental genotypes, loss of alleles, homologous recombination, and uniparental inheritance of kinetoplast maxicircle DNA. There are strong genetic parallels between these experimental hybrids and the genotypes among natural isolates of T. cruzi. In this instance, aneuploidy through nuclear hybridization results in recombination across far greater genetic distances than mendelian genetic exchange. This mechanism also parallels genome duplication.
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                Author and article information

                Journal
                Int J Parasitol
                Int. J. Parasitol
                International Journal for Parasitology
                Elsevier Science
                0020-7519
                1879-0135
                May 2011
                May 2011
                : 41
                : 6-10
                : 609-614
                Affiliations
                [a ]The London School of Hygiene and Tropical Medicine, Keppel Street, London WC1e 7HT, UK
                [b ]Lion House, 23 Onslow Road, Richmond, Surrey TW10 6QH, UK
                Author notes
                [* ]Corresponding author. Tel.: +44 207 927 2319; fax: +44 207 636 8739. martin.llewellyn@ 123456lshtm.ac.uk
                Article
                PARA3233
                10.1016/j.ijpara.2010.12.004
                3084450
                21232539
                4e3347e0-99bd-477f-8ffe-76701151a3d4
                © 2011 Elsevier Ltd.

                This document may be redistributed and reused, subject to certain conditions.

                Categories
                Article

                Parasitology

                trypansoma cruzi, infrapopulation, multiclonality, microsatellite, didelphis, chagas disease

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