Skrjabingylus chitwoodorum, Petrov, 1927, Petrov, 1927

Denham, Allie N., Hughes, Malorri R., Dowler, Robert C., Negovetich, Nicholas J. & Ammerman, Loren K., 2021, Genetic variation within a species of parasitic nematode, Skrjabingylus chitwoodorum, in skunks, Journal of Nematology 53 (1), pp. 1-8 : 4-5

Results

No significant pattern was seen between amplification of COI and correlation to purity ratio and/or concentration of template DNA. COI sequences were obtained from 39 samples of Skrjabingylus from 38 M. mephitis hosts and 1 S. p. interrupta host, representing areas of Texas (33), New York (3), and South Dakota (2). Maximum likelihood analysis of the fragment of COI composed of 492 base pairs recovered three distinct lineages: S. petrowi , S. nasicola , and a lineage comprising all S. chitwoodorum ( Fig. 3 ). Bootstrap analysis results using 1,000 replicates supported a distinct lineage of S. chitwoodorum that was divergent from the other two species of Skrjabingylus . Among all three species, 125 polymorphic sites were documented. Skrjabingylus chitwoodorum was 14.7% divergent from the outgroup taxon S. petrowi and 14.4% divergent from S. nasicola . A 15.9% difference was observed between S. nasicola and S. petrowi ( Table 1 ).

Within S. chitwoodorum samples, there was no obvious pattern of close geographic relationships other than a branch of four out-of-state samples, three from New York, and one from South Dakota, that were placed at the base of the tree and had bootstrap support of 70% ( Fig. 3 ). The sample of S. chitwoodorum from Spilogale ( ASK 11870) collected in South Dakota clustered closely with other samples collected from M. mephitis . However, the other two samples from South Dakota striped skunks were sister taxa (supported by a 93% bootstrap value) and clustered with a sinus worm from Sutton County, Texas. For the most part, among the samples from Texas there were no well-supported lineages that linked samples from the same county of collection. In total, 58 polymorphic sites occurred within the 39 S. chitwoodorum samples included in this study, 20 of which were parsimony-informative and 38 that were singleton sites. The overall average variation within the 33 Texas samples was 1.00% genetic divergence ( Table 1 ). The genetic diversity slightly increased when the six out-of-state samples were added into the analysis, showing a 1.29% average divergence. The highest divergence within Texas samples was 3.78% between Fannin ( ASK 13296) and Williamson ( ASK 9784) counties. When comparing Texas samples to the six out-of-state samples, the highest variation was 5.24% between Fannin ( ASK 13296) County in Texas and Brule ( ASK 14311) County in South Dakota.

In total, there were 22 COI haplotypes in S. chitwoodorum with three haplotypes being shared by two or more samples ( Fig. 4 ). The Bell County ( ASK 13294) haplotype was the most common and was shared with 10 other samples. Bailey County ( ASK 9931) shared a haplotype with five other samples from Texas (additional details available in Denham, 2020). Interestingly, the one sample of Skrjabingylus from the host species Spilogale in Brule County ( ASK 11870) of South Dakota shared a haplotype with two other counties, Clinton and Franklin County in New York ( ASK 12134 and ASK 12130). Nucleotide diversity, represented by π, was 3.06× 106. Mutational steps ranged between one to seven changes with the highest occurring between Travis County ( ASK 9750) and Fannin County ( ASK 13295).

Figures

Figure 3: Maximum likelihood phylogenetic tree of 492 base pair fragment of the cytochrome oxidase I gene for 44 samples of SKrjabingylus. Maximum likelihood analysis was performed using the best-fitting model, Hasegawa-Kishino-Yano of DNA substitution with Gamma distribution. Bootstrap values are based on 1000 replicates and values ≥70 are shown on branches. Number with prefix ASK identifies the specific host from which the sample was collected. Prefix KP is a Genbank accession number.

Figure 4: Median joining network showing the relationships among haplotypes of 44 samples of SKrjabingylus ChitWOOdOrum from hosts Mephitis mephitis and SpilOgale putOrius interrupta using COI mtDNA. Sizes of solid black circles correlate to shared haplotypes among multiple counties. Small open circles represent hypothetical haplotypes and ticks on branches represent number of mutational steps.