Octomitus genotypes

Seabolt, Matthew H., Alderisio, Kerri A., Xiao, Lihua & Roellig, Dawn M., 2021, Prevalence and molecular characterization of novel species of the Diplomonad genus Octomitus (Diplomonadida: Giardiinae) from wildlife in a New York watershed, International Journal for Parasitology: Parasites and Wildlife 14, pp. 267-272 : 269-270

3.3. Phylogenetic relationships among Octomitus genotypes

The final trimmed sequence alignment contained 74 sequences covering a 723 bp region of the 18S rDNA gene, including several variable regions. Maximum likelihood analysis confirmed genotype identification and estimated evolutionary relationships among genotypes. The resulting ML phylogeny is shown in Fig. 1 . The tree was rooted using the most divergent sequence, deer mouse genotype IV. Two distinct sequence variants (n = 12 and 15) of deer mouse genotype I were observed in the alignment, comprising one thymine insertion and one T-> C transition. While these mutations are consistent at the same sites

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* all genotypes here are novel and phylogenetically distinct from published O. intestinalis sequences ( Keeling et al., 2006; Helmy et al., 2018).

across samples in the alignment, these were considered the same genotype by bootstrap resampling in our phylogenetic analyses. Thus, the ML phylogeny confirmed 13 unique lineages with good branch support. Collapsing nodes with low statistical support revealed a polytomic node towards the base of the tree, from which arose four lineages: opossum genotypes I and II, a lineage containing the woodchuck genotype and deer mouse genotype III as sister taxa, and lastly, a lineage containing all remaining sequences, which are all from rodents with the exception of a single opossum host. Within this fourth lineage, a branch from murine hosts (the Norway rat and house mouse) is well supported, which incidentally includes the only sequence of vole genotype II as well as the Octomitus intestinalis reference sequence. Vole genotypes I and III clustered together as a distinct lineage, sister to a lineage containing the two most commonly identified genotypes (deer mouse genotypes I and II). ML analysis of the broader diplomonad alignment confirmed that the genotypes identified here form a well-supported monophyletic clade within the Diplomonads and confirmed the genus Octomitus as a sister lineage to Giardia ( Fig. 1 , inset).

Figures

Fig. 1. Phylogenetic relationships between 74 sequences of Octomitus representing 14 genotypes estimated by maximum likelihood analysis. The GTR + I + G model (gamma shape = 0.338, prop. invariable sites = 0.619) was chosen by jModelTest2 to be the best-fitting evolutionary model. Branches with less than 70% bootstrap support were not considered statistically robust and were collapsed during manual editing of the visualization. Inset: ML phylogeny computed from Octomitus genotypes aligned with the homologous region of available Diplomonad 18S rDNA sequences from Giardia, Spironucleus, Hexamita, Trimitus, and Enteromonas.