Phenotypic variation in a significant spore character in Kudoa (Myxosporea: Multivalvulida) species infecting brain tissue

Some Kudoa species display variations in the number of polar capsules in spores within an individual pseudocyst. Nonetheless, there is usually a dominant morphotype which forms a significant element of diagnosis. In 2007, a Kudoa isolate from whiting (spores with 5 (dominant) or 6 (minor) polar capsules) was characterized by Burger et al. (2007) as being 100% identical in SSU rDNA to Kudoa yasunagai (spores with 7 polar capsules) from a halibut, despite its obvious morphological differences. The authors hypothesized that either SSU rDNA had reached its level of resolution or that the genetic identity revealed conspecificity. To further investigate these hypotheses, SSU and LSU rDNA sequence data were coupled with principal components, correlation, and regression analyses of morphometric data from different kudoid isolates that infect brain tissue to determine the relationships between spore morphotypes and different kudoid isolates. The trends in morphometrics between the spores of particular isolates were so similar that it was concluded that the molecular results did indicate conspecificity rather than SSU reaching its level of resolution. This phenotypic influence on a significant diagnostic character within the Kudoidae has a major impact on the diagnosis of this, and potentially other, pathogenic species.