title: Strong genetic structure revealed by multilocus patterns of variation in Giardia duodenalis isolates of patients from Galicia (NW-Iberian Peninsula).
abstract: We report a survey of genetic variation at three coding loci in Giardia duodenalis of assemblages A and B obtained from stool samples of patients from Santiago de Compostela (Galicia, NW-Iberian Peninsula). The mean pooled synonymous diversity for assemblage A was nearly five times lower than for assemblage B (0.77%±0.30% and 4.14%±1.65%, respectively). Synonymous variation in both assemblages was in mutation-drift equilibrium and an excess of low-frequency nonsynonymous variants suggested the action of purifying selection at the three loci. Differences between isolates contributed to 40% and 60% of total genetic variance in assemblages A and B, respectively, which revealed a significant genetic structure. These results, together with the lack of evidence for recombination, support that (i) Giardia assemblages A and B are in demographic equilibrium and behave as two genetically isolated populations, (ii) infections are initiated by a reduced number of individuals, which may be genetically diverse and even belong to different assemblages, and (iii) parasites reproduce clonally within the host. However, the observation of invariant loci in some isolates means that mechanisms for the homogenization of the genetic content of the two diploid nuclei in each individual must exist.
authors.affiliation: Grupo de Medicina Xenómica, Centro de Investigación en Medicina Molecular e Enfermidades Crónicas da Universidade de Santiago de Compostela (CIMUS), Avda. Barcelona s/n, 15782 Santiago, Galicia, Spain; Xenómica Comparada de Parasitos Humanos, Instituto de Investigacións Sanitarias de Santiago (IDIS), Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain. Electronic address: luisbgg@gmail.com.
authors.forename: Luis B
authors.initials: LB
authors.lastname: Gabín-García
authors.affiliation: Grupo de Medicina Xenómica, Centro de Investigación en Medicina Molecular e Enfermidades Crónicas da Universidade de Santiago de Compostela (CIMUS), Avda. Barcelona s/n, 15782 Santiago, Galicia, Spain; Xenómica Comparada de Parasitos Humanos, Instituto de Investigacións Sanitarias de Santiago (IDIS), Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain.
authors.forename: Carolina
authors.initials: C
authors.lastname: Bartolomé
authors.affiliation: Grupo de Medicina Xenómica, Centro de Investigación en Medicina Molecular e Enfermidades Crónicas da Universidade de Santiago de Compostela (CIMUS), Avda. Barcelona s/n, 15782 Santiago, Galicia, Spain; Xenómica Comparada de Parasitos Humanos, Instituto de Investigacións Sanitarias de Santiago (IDIS), Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain.
authors.forename: José L
authors.initials: JL
authors.lastname: Abal-Fabeiro
authors.affiliation: Xenómica Comparada de Parasitos Humanos, Instituto de Investigacións Sanitarias de Santiago (IDIS), Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain; Servizo de Microbioloxía e Parasitoloxía, Complexo Hospitalario Universitario de Santiago, Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain.
authors.forename: Santiago
authors.initials: S
authors.lastname: Méndez
authors.affiliation: Xenómica Comparada de Parasitos Humanos, Instituto de Investigacións Sanitarias de Santiago (IDIS), Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain; Servizo de Microbioloxía e Parasitoloxía, Complexo Hospitalario Universitario de Santiago, Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Llovo
authors.affiliation: Grupo de Medicina Xenómica, Centro de Investigación en Medicina Molecular e Enfermidades Crónicas da Universidade de Santiago de Compostela (CIMUS), Avda. Barcelona s/n, 15782 Santiago, Galicia, Spain; Xenómica Comparada de Parasitos Humanos, Instituto de Investigacións Sanitarias de Santiago (IDIS), Travesia da Choupana s/n, 15706 Santiago, Galicia, Spain.
authors.forename: Xulio
authors.initials: X
authors.lastname: Maside
mesh_terms: D001483:Base Sequence; D017124:Conserved Sequence; D019143:Evolution, Molecular; D017125:Genes, Protozoan; D049810:Genetic Speciation; D016829:Giardia lamblia / Q000235:genetics* / Q000302:isolation & purification; D005873:Giardiasis / Q000469:parasitology*; D006239:Haplotypes; D006801:Humans; D058885:Multilocus Sequence Typing; D010802:Phylogeny; D013030:Spain
keywords: Genetic diversity; Giardia duodenalis; PCR cloning; Population structure; Recombination