There are numerous species of parasitic protists which were described based upon cell morphology and host species in the beginning of the past century. Only scarce morphological description and no type collection materials are often available for those.
Finding today a parasite with similar morphology (lots of them are similar at light microscopy level) in the same host, should I identify it as that old species? What to do if there are no traits for differentiation between a new isolate and an old insufficiently described species?
Thanks, Marc,
I am already reassured by the fact I "not have the problem with anamorph and teleomorph names"!
Hello Yuri. I think the best option would be to consider your findings as the same previously described if 1) the host species is the same and 2) there are no (significative) morphological differences between your isolate and the "old" species. Have in mind that different staining methods could lead to apparently morphological differences, so be careful with this. What you can do is a redescription of the species by including more data (i.e., morphology under electron microscopy, genetic data) that will be helpful for future work. It is also possible, specially with the genetic data, that you could find surprising results that could justify considering a new species besides the old one.
A redescription is the better way. You should show that the data available do not differ from previous description and then proceed to a new description adding all extra data available and new type material.
In case if this is representative of protist group which are well distinguished morphologically the way is redescription. However among the parasitic protists there are some group which indistinguishable without molecular data now. Thus the species identification would be impossible. In this case it shoiuld be better to marked the old species name as nomen dubium and described the species your find as a new species but using a sequencing for description.
Dear Colleague,
The parasitic protist species you are working on might be or might not be the same as those described 100 years ago. Of note, a century is enough time for a parasite to evolve, given the multifactorial variation of "living" conditions with time. I believe the issue is not [giving a new name or not]. All depends on what description you do of the protist. To achieve this, you should take advantage of the new physical and molecular techniques.
Hello Yuri
You should:
1- find some fossils of that old organism.
2- extracted its DNA by a suitable method as well some present organism.
3- choose some constant regions in genome.
4- check the similarity and identity of old and current organisms.
5- take your answer considering some scientific documents.
there would be no probs be the fossils available for DNA extraction!!!! The point is there's usually but a few lines of description and a hand-drawn picture of the parasite spores/zoites/cysts....
Dear Yuri,
The best description and morphological based diagnosis of Vet Protozoa you can find is in Levine ND's text book published in 1986. This book showed lots of detailed graphic of species discovered at that time. Whenever I have to diagnose such parasites, I always go back to this book and include some specific DNA sequences available in the Genbank database.
For example, we always confused between Balantidium and Buxtonella, ones found in swine and others in cattle, whether they are the same species. Levine described them as the ex-conjugant of others with the confused morphological undifferentiated. I encouraged students to include their DNA sequences retrieved from the samples compared to the Genbank database. I don't know what the outcome is, but this process of diagnosis is agreed among colleagues.
I guess we are in the period of species identification combined between morphological and molecular biological bases. This protocol of diagnostic process could apply to any other living organisms found today too.
Hy Yuri, I think as the other collegues, clasiffication of the protiest species has been changed the last time with the molecular biology instruments, also today we are in face to new paradigms and clasiffications. But I found also this question very good, but changing the discussion about what happen with the protiist maintained in the laboratory for years, supporting of the sceintific research and in fact, that the specific sequences of DNA were not changed, then, could us considered those models representative of protist behavior in nature? Is the presence of the specific sequences of DNA enough? Colors and morphology, by the way, could change depending of the culture or isolation conditions.
There are a general complaint about appropiate preservation of protist type material. It is highly recommendable to follow certain advises. See the atached files
Please, take a look to our paper :
Molecular phylogenetic and zoospore ultrastructural analyses of Chytridium olla establish the limits of a monophyletic Chytridiales.
Article Molecular phylogenetic and zoospore ultrastructural analyses...
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