I received the following comments from Michel Tibayrenc yesterday
and I am forwarding them with his permission as I think they are
C. Graham Clark,
Laboratory of Parasitic Diseases,
National Institutes of Health,
Bethesda, MD 20892
e-mail: cge at cu.nih.gov
I call 'agamospecies'
species that are predominantly asexual, and so, don't meet
the biological concept of species (in sexual organisms, as you know,
species are defined relatively to one another by the possibility or
not to freely exchange genes: dogs and cats are different species
because they don't interbreed. In Trypanosomes, Leishmania, Amoeba,
the status of sex is at best unclear. So one can't rely on the
concept of species, the only one that has a clear and simple (but not
always easy to use) genetic background.
Species in parasitic protozoa are most often defined either on
biological/medical characters (virulence, clinical form of a disease)
or on a phylogenetic basis (when the phylogenetic divergence is
'sufficient', it is considered that different species should be
cf the notion of genospecies in bacteria), or on a combination of
biological/medical plus phylogeny, which is preferable. The situation
in Entamoeba in which two radically dissimilar phylogenetic clusters
coincide with different medical properties (virulence/avirulence) is
a paradigm to describe useful species. When I say that species
used in microbiology are arbitrary, it does not mean that they are not
good. Actually, they are the only ones we have. But the boundaries
only on the opinion of experts. If the experts are good and they think
that it is needed to create a new species, OK for the new species.
I think like you that it is misleading to describe hundreds of species
on the basis of phylogenies. Exactly what the leishmaniacs are doing.
(tibayren at orstom.fr)