Naming species

Mon Feb 28 14:53:32 EST 1994

I would like to initiate a discussion on the topic of species
naming in morphologically conservative protist groups that
appear to lack a sexual cycle.

Morphological variation has historically provided
the most widely accepted criteria for species description.
However, many protist groups exist where the traits available
are limited and those that exist are of uncertain value, such as in
my own nemesis, the amebae.

We are now in a position to examine such organisms at the
molecular level, using isoenzymes, DNA sequence analysis, etc.
However, this does not seem to be helping. It is known that
bona fide classically-defined species of Tetrahymena can have
identical small subunit ribosomal RNA gene sequences while different
isolates of the species Trypanosoma cruzi and Giardia lamblia can
exhibit significant rRNA sequence variation. Clearly, giving different
names to these sequence variants would be counterproductive.
However, the degree of intraspecific variation is certainly an
important feature to be aware of when working with such species.

My questions are: Is there a way to convey a high degree of
continuous intra-specific variation without causing confusion by
the creation of additional taxa?;

Is the creation of new species based on molecular data (isoenzymes,
immunological cross-reactivity, DNA sequences) alone acceptable,
or must there be biological (morphology, niche, growth, etc)
differences as well?;

Is it rational to expect a pan-protista set of criteria for the
recognition of new species or will every group have to be handled

I do not expect a consensus to emerge but I am interested in
hearing other points of view......


C. Graham Clark,
Laboratory of Parasitic Diseases,
National Institutes of Health,
Bethesda, MD 20892

Ph.: 301-496-4740
e-mail: cge at

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