Absence of genetic structure in Baylisascaris schroederi populations, a giant panda parasite, determined by mitochondrial sequencing

Abstract

BackgroundInfection 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.MethodsBased 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).ResultsFor 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.ConclusionsThese 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0606-3) contains supplementary material, which is available to authorized users.

The population genetics of parasitic nematodes of wild animals

“…Baylisascaris schroederi is a nematode thought to be specific to giant pandas ( Ailuropoda melanoleuca ). Sequence analysis of both ITS and mtDNA have shown a lack of genetic differentiation among B. schroederi from geographically isolated panda populations [ 124 – 127 ], which is surprising because pandas do not migrate among populations, and pandas from each of these populations are themselves genetically differentiated [ 128 ]. The likely explanation for this difference between host and parasite population genetics is that B. schroederi has a much larger Ne than its host [ 129 ] and so undergoes population differentiation more slowly.…”

“…Thus, while there may have been time for panda populations to differentiate through genetic drift in the 200 years since habitat fragmentation began [ 130 ], drift may not have been fast enough to yet differentiate B. schroederi populations. It has also been suggested that B. schroederi gene flow may occur among panda populations in the absence of panda movement, for example through association with a presently unknown paratenic host [ 127 ].…”

Parasites of the Giant Panda: A Risk Factor in the Conservation of a Species

“…the Minshan, Qionglai and Qinling mountain ranges). A low level of genetic diversity but a high level of gene flow in worms suggested the potential for a rapid spread of drug resistance in B. schroederi (see Xie et al, 2014). Third, Zhao et al (2014) did not find support for the genetic substructuring within B. schroederi among samples from the Qinling mountains and one sample from Sichuan province using portions of the mitochondrial genes cytb, cox3 and nad5.…”

“…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. Again, these authors found no discernable genetic difference in worms among the populations from distinct habitats of the giant panda (i.e.…”

Fatty-binding protein and galectin of Baylisascaris schroederi: Prokaryotic expression and preliminary evaluation of serodiagnostic potential

“…schroederi eggs in feces of infected giant pandas. However, after eggs containing L 2 larvae hatch in the host, it takes 77–93 days before they mature and begin to ovulate [ 11 ]. Thus, the currently available methods are unsuitable for early detection of B .…”