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I was not going to tackle the question as to the taxonomic status of the
visceral parasites raised by Dick but since Jorge bravely took up the
challenge I will just add the following to his comments.<br>
<x-tab> </x-tab>Molecular
tools reveal genetic diversity that is not mirrored by the more classical
methods such as isoenzymes. Taxonomic methods show that there are two
distinct clades, one which corresponds to the <i>donovani</i>
parasites and another to the <i>infantum</i> parasites. Within the latter
distinctions are less well defined and the use of subspecies for these
populations is in my opinion justifiable. For instance it has been shown
that <i>i.infantum</i> and <i>i.chagasi</i> can be distinguished by kDNA
fragment patterns, radio-respirometry and certain promastigote surface
proteins.<br>
<x-tab> </x-tab>I agree
fully with Dick Ashford that differences in geographical distribution is
not a character that can be used to define taxa. However, we have
to remember that separation of populations leads to genetic
isolation. So differences in geographical distributions of
parasites that man himself takes with him around the world will probably
be of lesser importance in causing genetic isolation than those whose
reservoirs are wild animals, such as many of the neotropical
<i>Leishmania </i>(<i>Viannia</i>) species. Thus differences in
geographical distribution is a backcloth to speciation but not a
character.<br>
<x-tab> </x-tab>As a
closing shot I would just like to say that rules are made by man and
species by nature. At the moment I am not sure if the two are completely
compatable.<br>
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