title: Globally diverse Toxoplasma gondii isolates comprise six major clades originating from a small number of distinct ancestral lineages.
abstract: Marked phenotypic variation characterizes isolates of Toxoplasma gondii, a ubiquitous zoonotic parasite that serves as an important experimental model for studying apicomplexan parasites. Progress in identifying the heritable basis for clinically and epidemiologically significant differences requires a robust system for describing and interpreting evolutionary subdivisions in this prevalent pathogen. To develop such a system, we have examined more than 950 isolates collected from around the world and genotyped them using three independent sets of polymorphic DNA markers, sampling 30 loci distributed across all nuclear chromosomes as well as the plastid genome. Our studies reveal a biphasic pattern consisting of regions in the Northern Hemisphere where a few, highly clonal and abundant lineages predominate; elsewhere, and especially in portions of South America are characterized by a diverse assemblage of less common genotypes that show greater evidence of recombination. Clustering methods were used to organize the marked genetic diversity of 138 unique genotypes into 15 haplogroups that collectively define six major clades. Analysis of gene flow indicates that a small number of ancestral lineages gave rise to the existing diversity through a process of limited admixture. Identification of reference strains for these major groups should facilitate future studies on comparative genomics and identification of genes that control important biological phenotypes including pathogenesis and transmission.
authors.affiliation: Department of Microbiology, University of Tennessee, Knoxville, TN 37996, USA.
authors.forename: Chunlei
authors.initials: C
authors.lastname: Su
authors.forename: Asis
authors.initials: A
authors.lastname: Khan
authors.forename: Peng
authors.initials: P
authors.lastname: Zhou
authors.forename: Debashree
authors.initials: D
authors.lastname: Majumdar
authors.forename: Daniel
authors.initials: D
authors.lastname: Ajzenberg
authors.forename: Marie-Laure
authors.initials: ML
authors.lastname: Dardé
authors.forename: Xing-Quan
authors.initials: XQ
authors.lastname: Zhu
authors.forename: James W
authors.initials: JW
authors.lastname: Ajioka
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Rosenthal
authors.forename: Jitender P
authors.initials: JP
authors.lastname: Dubey
authors.forename: L David
authors.initials: LD
authors.lastname: Sibley
mesh_terms: D001483:Base Sequence; D056426:Genetic Loci / Q000235:genetics; D005819:Genetic Markers; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes / Q000235:genetics; D007438:Introns / Q000235:genetics; D018895:Microsatellite Repeats / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D012150:Polymorphism, Restriction Fragment Length; D011157:Population Dynamics; D014122:Toxoplasma / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D005819:Genetic Markers