Baylisascaris

Camp, Lauren E., Radke, Marc R., Shihabi, Danny M., Pagan, Christopher, Yang, Guangyou & Nadler, Steven A., 2018, Molecular phylogenetics and species-level systematics of Baylisascaris, International Journal for Parasitology: Parasites and Wildlife 7 (3), pp. 450-462 : 456-458

4.1. Phylogeny of Baylisascaris

In the present study, relationships among seven species of Baylisascaris were analyzed using multiple loci, including one species with no previously published sequence data – B. tasmaniensis . Monophyly of the genus Baylisascaris was supported in all trees based on combined sequence data ( Figs. 1–3 , Figs. S1 , and S2) and in most single gene trees (Tables S7 and S8). Baylisascaris devosi was sister to isolates of B. columnaris and B. procyonis in all trees based on combined sequence data with very high or absolute support ( Figs. 1–3 ). The inclusion of B. devosi in clade 1 is not unexpected given a previous analysis of rDNA data that resolved B. devosi and B. potosis as sister species ( Tranbenkova and Spiridonov, 2017) and considering that Sprent (1968) originally grouped B. devosi with B. columnaris , B. procyonis , and B. laevis based on reduced size of cervical alae and overall body size. In addition, hosts of three of these five species (not B. laevis ) are from the superfamily Musteloidea : B. potosis infects Potos flavus (kinkajou) and B. devosi infects Martes americana (American marten), Martes zibellina (sable), Pekania pennanti (fisher), and Gulo gulo (wolverine). Several of these B. devosi hosts co-occur in parts of the northern and western extents of raccoon ( B. procyonis ) and striped skunk ( B. columnaris ) ranges. In addition, analyses of previously published sequences (limited data,

often single genes) for B. potosis and B. venezuelensis confirmed their placement in clade 1 and clade 2, respectively ( Fig. S3-S 5).

Baylisascaris tasmaniensis was also part of a monophyletic Baylisascaris , and although the position of this species was inconsistent in trees based on single genes (Tables S7 and S8), the combined analyses often resolved this species as part of clade 2, sister to the parasites from ursids and red panda ( Figs. 1–3 ). This relationship had absolute BPP support for combined nuclear genes and the combined analysis of all genes, and lower support for mitochondrial genes (0.90), but this relationship was not obtained for datasets that included hars1 ( Figs. S1 ,

S 2 ).

Limited research has been done on B. tasmaniensis since the work of Sprent (1970) and colleagues ( Sprent et al., 1973). Sprent (1970) suggested that B. tasmaniensis was morphologically similar to B. melis of European badgers and B. transfuga of bears, because all three species have noticeable cervical alae. However, Sprent et al. (1973) also noted similarities between larvae of B. tasmaniensis and B. devosi in terms of development, behavior, and morphology. Sequence data from B. melis was not available, but sequences of B. devosi and two Baylisascaris species from bears were analyzed. Baylisascaris tasmaniensis was part of a monophyletic group containing bear parasites in eight of 10 trees based on combined sequence data with moderate to absolute support ( Figs. 1–3 ). More complete sampling of Baylisascaris species has the potential to increase resolution in molecular phylogenetic trees, and for described species this would require adding B. melis and B. laevis . However, recent descriptions of two new species ( Tokiwa et al., 2014; Pérez Mata et al., 2016) suggests that Baylisascaris biodiversity is incompletely known and requires additional investigation.

As Sprent et al. (1973) noted, it is not clear how B. tasmaniensis initially infected Tasmanian devils ( Sarcophilus harrisii ) and quolls ( Dasyurus species) because the other definitive hosts of Baylisascaris spp. are arctoid carnivorans, which are not found in Australia or Tasmania. Sprent (1970) provided two potential explanations: 1) marsupials originally occurring in Australia had a phylogenetic relationship with arctoid carnivorans and ascaridoid nematodes were shared between these host groups; and 2) convergent evolution of ascaridoids, due to infecting hosts that occupy similar niches, led to the morphological similarity between B. tasmaniensis and other Baylisascaris species ( Sprent, 1970). A recent phylogenetic analysis of mammals provides no support for a close phylogenetic relationship between arctoid carnivorans and marsupials ( Tarver et al., 2016). Sprent's second hypothesis of convergent evolution from a non- Baylisascaris ascaridoid ancestor is contradicted by the inclusion of B. tasmaniensis as part of a monophyletic Baylisascaris in the present study. Sprent et al. (1973) also noted the possibility of B. transfuga occurring in bears at the far southern extent of South East Asia but did not directly connect this idea to the colonization of marsupial hosts in the Australian region. Sun bears ( Helarctos malayanus ) and the Asiatic black bear ( Ursus thibetanus , syn. U. torquatus ) occur in SE Asia, and both species have been recorded as hosts of Baylisascaris ( Sprent, 1968) . The potential colonization of marsupials by Baylisascaris from SE Asian bears would need to be explained relative to the apparent restricted host range of Baylisascaris species in Australian marsupials. Additional information on the phylogenetic relationships of Baylisascaris species in bears and B. tasmaniensis may be key to determining whether the origin of Baylisascaris in dasyurids was due to a host-colonization (switching) event.

According to Kazacos (2001, 2016), baylisascariasis in humans can also be caused by B. columnaris , B. melis , B. devosi , B. transfuga , and B. tasmaniensis . Baylisascaris procyonis is believed to be the primary cause of baylisascariasis in paratenic hosts and humans, but the lack of a clear, rapid molecular diagnostic test that can specifically identify B. procyonis means that we do not know the health risk of other Baylisascaris species. Clinical diagnosis of baylisascariasis is primarily based on serological tests, but these tests cannot discriminate among Baylisascaris species ( Graeff-Teixeira et al., 2016). In such cases, it would be useful to diagnose specimens or potential environmental sources of Baylisascaris using a DNA sequence-based method. One approach is to use phylogenetic analysis of gene sequence data to place unknown Baylisascaris samples in an evolutionary tree ( Hoberg et al., 2018). This approach does not depend upon predefined species-specific sequence signatures and can accommodate previously unknown variation in the sequences during the analysis. For example, phylogenetic analysis of the three mitochondrial genes used herein (12S, cox-1, cox-2) provides a well-resolved tree and sequencing these genes does not normally require cloning. In addition, size (electrophoretic) comparisons of ard1 amplicons can distinguish between taxa in the two main Baylisascaris clades as B. ailuri , B. schroederi , and both B. transfuga isolates have a continuous 222 bp gap in ard- 1 that is not present in B. columnaris , B. procyonis , B. devosi , or B. tasmaniensis .

Figures

Fig. 1. Bayesian consensus tree based on combined FULL data (8 genes; not including hars1). Branch lengths are scaled to the expected number of substitutions per site. Numbers above nodes are Bayesian posterior probabilities, shown when 0.90 and greater.

Fig. 2. Bayesian consensus tree based on FULL data from nuclear genes (5 genes; not including hars1). Branch lengths are scaled to the expected number of substitutions per site. Numbers above nodes represent Bayesian posterior probabilities, shown when 0.90 and greater.

Fig. 3. Bayesian consensus tree based on FULL mitochondrial gene sequences (3 genes). Branch lengths are scaled to the expected number of substitutions per site. Numbers above nodes represent Bayesian posterior probabilities, shown when 0.90 and greater.