Lectotype rule-change explained

[christian thompson]

Dear Mick et alia:

What Philip Tubbs said is true. That is, "In fact, the intention of the
change was to deter designations from being made simply as curatorial
tidying-up."

But from that it does not necessarily follow what Mick Webb believes: That
is lectotypes should only be designated when there is taxonomic
uncertainity.  This issue was well argued between Curtis Sabrosky and Roger
Crosskey years ago with Dick Vane-Wright putting in the last two bits of it.
(see Bulletin British Museum (Natural History) Entomology 32: 17-64 1975).

The question to ask yourself, WHY DESIGNATE HOLOTYPES? Even if you are sure
of your taxonomic concept, a syntypic series is far better according to the
logic of Webb, Crosskey, et alia, because it may allow for FUTURE change in
the application of the name if you were wrong about your taxonomic concept.


History has proved that with taxonomic progress new and better characters
are discovered, frequently leading to revision of prior taxonomic concepts
(circumscriptions, etc.).  Hence, some people concluded having designated a
SINGLE specimen (Holotype) will allow proper assignment of the name to one
of the revised taxonomic concepts. This does not guarantee that the name
will necessarily follow what may be the common perceived understanding of
that nominal taxon, etc., but it will ensure the name will belong to a
subset of the original author's concept.

Now in doing revisionary work, that is, when one re-defines older taxa,
providing new and better characters, etc., which subsequent workers will use
to identify, etc., those revised taxa, the argument goes, where the nominal
taxon is defined by multiple specimens, especially multiple specimens which
the revisor may not have seen all of them**, the revisor should select a
lectotype, so just like a holotype of a new species, subsequent workers will
be ensured that name will follow in part the revisor's concept.

The simple point remains. Ultimately the only way to fix and ensure
stability of the name for a nominal  species taxon is to have a single
specimen as its standard. This is NOMENCLATURAL stability. That is what the
rules are about.

Yes, there may be Taxonomic instability.  And taxonomic progress, new and
better characters, etc.,  frequently leads to old taxonomic concepts being
divided up into new ones. And that may mean some or all prior literature
(research) may not necessarily follow the revised set of names. If this is a
real concern, then look at a system, like the Phylo Code, which doesn't use
types!  (But do remember under the ICZN, the use of the plenary powers can
change anything!)


**this is especially important. Remember for many older species, such as
those of Linnaeus, the syntypic series includes those specimens upon which
earlier observations which Linnaeus cited were based. So, the syntypic
series may include far more than the specimens in the Linnaean collection in
London. One can not restrict a syntypic series to a subset, one can only
select a lectotype or not.  So, the only way to ensure that one's revised
concept is restricted to the syntypes studied is to select a lectotype.
This is also true for later described species. For example, while some
museums, like the BM(NH), like to think that they hold all the remaining
syntypes of species described by their earlier curators, many of those
syntypes have found their way into other collections. Francis Walker sold
"duplicates" of many of his species to Melbourne! The Biologia
Centrali-Americana material is scattered everywhere. Et cetera

F. Christian Thompson
Systematic Entomology Lab., ARS, USDA
Smithsonian Institution
Washington, D. C. 20560-0169
(202) 382-1800 voice
(202) 786-9422 FAX
cthompso at sel.barc.usda.gov
visit our Diptera site at www.diptera.org