title: Absence of genetic structure in Baylisascaris schroederi populations, a giant panda parasite, determined by mitochondrial sequencing.
abstract: BACKGROUND
  Infection with the parasitic nematode, Baylisascaris schroederi (Ascaridida: Nematoda), is one of the most important causes of death in giant pandas, and was responsible for half of deaths between 2001 and 2005. Mitochondrial (mt) DNA sequences of parasites can unveil their genetic diversity and depict their likely dynamic evolution and therefore may provide insights into parasite survival and responses to host changes, as well as parasite control.
  
  
  METHODS
  Based on previous studies, the present study further annotated the genetic variability and structure of B. schroederi populations by combining two different mtDNA markers, ATPase subunit 6 (atp6) and cytochrome c oxidase subunit I (cox1). Both sequences were completely amplified and genetically analyzed among 57 B. schroederi isolates, which were individually collected from ten geographical regions located in three important giant panda habitats in China (Minshan, Qionglai and Qinling mountain ranges).
  
  
  RESULTS
  For the DNA dataset, we identified 20 haplotypes of atp6, 24 haplotypes of cox1, and 39 haplotypes of atp6 + cox1. Further haplotype network and phylogenetic analyses demonstrated that B. schroederi populations were predominantly driven by three common haplotypes, atp6 A1, cox1 C10, and atp6 + cox1 H11. However, due to low rates of gene differentiation between the three populations, both the atp6 and cox1 genes appeared not to be significantly associated with geographical divisions. In addition, high gene flow was detected among the B. schroederi populations, consistent with previous studies, suggesting that this parasite may be essentially homogenous across endemic areas. Finally, neutrality tests and mismatch analysis indicated that B. schroederi had undergone earlier demographic expansion.
  
  
  CONCLUSIONS
  These results confirmed that B. schroederi populations do not follow a pattern of isolation by distance, further revealing the possible existence of physical connections before geographic separation. This study should also contribute to an improved understanding of the population genetics and evolutionary biology of B. schroederi and assist in the control of baylisascariasis in giant pandas.
authors.affiliation: Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, Ya'an, 625014, China. zhandegaokandey123@163.com.
authors.forename: Yue
authors.initials: Y
authors.lastname: Xie
authors.affiliation: Centre for Animal Diseases Control and Prevention, Dachuan Animal Husbandry Bureau, Dazhou, 623000, China. zhouxuan198866@163.com.
authors.forename: Xuan
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Chengdu Research Base of Giant Panda Breeding, Chengdu, 610081, China. parasitology513@163.com.
authors.forename: Zhihe
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Chengdu Research Base of Giant Panda Breeding, Chengdu, 610081, China. susieconan@vip.qq.com.
authors.forename: Chengdong
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, Ya'an, 625014, China. sunyun062@163.com.
authors.forename: Yun
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, Ya'an, 625014, China. kevinlau1990@hotmail.com.
authors.forename: Tianyu
authors.initials: T
authors.lastname: Liu
authors.affiliation: Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, Ya'an, 625014, China. guxiaobin198225@126.com.
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Gu
authors.affiliation: Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, Ya'an, 625014, China. wangtao0614@gmail.com.
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.affiliation: Department of Chemistry, College of Life and Basic Science, Sichuan Agricultural University, Ya'an, 625014, China. pxuerong@yahoo.com.cn.
authors.forename: Xuerong
authors.initials: X
authors.lastname: Peng
authors.affiliation: Department of Parasitology, College of Veterinary Medicine, Sichuan Agricultural University, Ya'an, 625014, China. guangyou1963@aliyun.com.
authors.forename: Guangyou
authors.initials: G
authors.lastname: Yang
mesh_terms: D000818:Animals; D017191:Ascaridida Infections / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary*; D001199:Ascaridoidea / Q000235:genetics* / Q000302:isolation & purification; D001483:Base Sequence; D002681:China / Q000453:epidemiology; D018509:DNA, Helminth / Q000737:chemistry / Q000235:genetics; D004272:DNA, Mitochondrial / Q000737:chemistry / Q000235:genetics; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes; D008928:Mitochondria / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA / Q000662:veterinary; D001503:Ursidae / Q000469:parasitology*
chemical_list: D018509:DNA, Helminth; D004272:DNA, Mitochondrial