Analysis of the genetic diversity of the nematode parasite Baylisascaris schroederi from wild giant pandas in different mountain ranges in China

Abstract

BackgroundBaylisascaris schroederi is one of the most common nematodes of the giant panda, and can cause severe baylisascarosis in both wild and captive giant pandas. Previous studies of the giant pandas indicated that this population is genetically distinct, implying the presence of a new subspecies. Based on the co-evolution between the parasite and the host, the aim of this study was to investigate the genetic differentiation in the B. schroederi population collected from giant pandas inhabiting different mountain ranges, and further to identify whether the evolution of this parasite correlates with the evolution of giant pandas.MethodsIn this study, 48 B. schroederi were collected from 28 wild giant pandas inhabiting the Qinling, Minshan and Qionglai mountain ranges in China. The complete sequence of the mitochondrial cytochrome b (mtCytb) gene was amplified by PCR, and the corresponding population genetic diversity of the three mountain populations was determined. In addition, we discussed the evolutionary relationship between B. schroederi and its host giant panda.ResultsFor the DNA dataset, insignificant Fst values and a significant, high level of gene flow were detected among the three mountain populations of B. schroederi, and high genetic variation within populations and a low genetic distance were observed. Both phylogenetic analyses and network mapping of the 16 haplotypes revealed a dispersed pattern and an absence of branches strictly corresponding to the three mountain range sampling sites. Neutrality tests and mismatch analysis indicated that B. schroederi experienced a population expansion in the past.ConclusionsTaken together, the dispersed haplotype map, extremely high gene flow among the three populations of B. schroederi, low genetic structure and rapid evolutionary rate suggest that the B. schroederi populations did not follow a pattern of isolation by distance, indicating the existence of physical connections before these populations became geographically separated.

Genomic Epidemiology in Filarial Nematodes: Transforming the Basis for Elimination Program Decisions

“…In particular, if a population decreases in size, as might be expected as transmission decreases during successive rounds of MDA, the chance that changes in allele frequencies are stochastic rather than deterministic increases: the genetic diversity overall decreases (e.g., Schistosoma mansoni: Coeli et al, 2013), but the fate of individual alleles is unpredictable, and some may increase due to genetic drift caused by population decline. Another challenge is that, prior to treatment, parasite populations can be quite large (i.e., they have a high effective population size; Blouin et al, 1995;Blouin et al, 1999;Zhou et al, 2013;Rodelsperger et al, 2014;Jan et al, 2016), which means they have ample genetic variation, so genetic variation contributing to a poor response phenotype may be present at different frequencies and at different loci in different parasite populations (e.g., Haemonchus contortus, Gilleard and Redman, 2016). Furthermore, once MDA begins, mating and recombination could create new combinations of alleles from different genes, which may also decrease response to ivermectin.…”

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“…Other studies attempted to resolve the same issue using various mitochondrial gene markers. First, Zhou et al (2013a) used the cytb gene and concluded that there was a high rate of gene flow among three populations of B. schroederi representing the two recognised subspecies. Second, Xie et al (2014Xie et al ( , 2015b used portions of the mitochondrial cox1, atp6 and 12S rRNA genes, which displayed very few parsimony informative sites.…”

High genetic diversity in the harvestmanGeraeocormobius sylvarum(Arachnida, Opiliones, Gonyleptidae) from subtropical forests in north-eastern Argentina revealed by mitochondrial DNA sequences

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“…One powerful strategy to test these alternative hypotheses for the disjunction (historical versus introduction) is the population analysis using suitable molecular markers. Understanding the organismal biodiversity based on the analysis of genetic variation has important implications for the study of the evolutionary history and the population genetic structure (Zhou et al 2013). Population genetics analyses in harvestmen are relatively scarce (e.g.…”