[Taxacom] type species for a genus - lectotype?

[Dan Lahr]

Hi Karolina,

This is a common problem in taxonomy of microbial eukaryotes:
establishing the taxonomic identity of traditionally described
organisms when modern data is available (modern data in this case may
be molecular, but often times it is also ultrastructural data, TEMs or
SEMs, or even better drawing descriptions). The problem is complicated
because types are often figures, and in many fields there was no
tradition of depositing cultures.  There is no real solution for this,
as far as I know, in the ICZN. I'm not so familiar with the ICBN,
maybe other people can help.

In my experience, the decision will almost always be subjective, so
forget about objective synonyms. There is no way of saying for sure
that Bracteacoccus aggregatus depicted in figure XX of the original
description is indeed the strain you're working with.  However,
depending on the morphological characters that were described and
compared to the ones you're looking at, your strain may be consistent
with the original description.

The solution I've found is to deal with taxonomic concepts that are
inseparable from each other, in a list of non-distinct nominal taxa.
This somewhat overlaps with the concept of "chresonyms", i.e.,
synonyms on the basis of usage, Dubois has dealt with this issue to a
great extent.  This makes explicit that your subjective interpretation
is that these nominal taxa are indistinct, but preserves the
information from previous authors.  I've dealt with this issue at
length in the following works on testate amoeba:

- Lahr DJG, Bergmann PJ, Lopes SG (2008). Taxonomic identity in
microbial eukaryotes: a practical approach using the testate amoeba
Centropyxis to resolve conflicts between old and new taxonomic
descriptions. J. Eukaryot. Microbiol. 55 (5): 409–16.
doi:10.1111/j.1550-7408.2008.00339.x. PMID 19017061.

- Lahr DJG, Lopes SG (2009). Evaluating the Taxonomic Identity in Four
Species of the Lobose Testate Amoebae Genus Arcella Ehrenberg, 1832.
Acta Protozoologica. 48(2):127-142

I suspect in your case the solution will be either:

1. B. minor and B. aggregatus are impossible to distinguish from each
other (for lack of objective data), so B. aggregatus gets priority for
the name, and B. minor is listed as a non-distinct taxon, in which
case you can use that description to match your strain and propose a
lectotype.

2. B. minor and B. aggregatus have enough different characteristics
(in your opinion) to be separated. In which case you call your strain
B. minor and leave B. aggregatus behind.  You can propose a new type
species for the genus by submitting your case to the commission, it
seems reasonable that if the type species has no usable type, and has
not been found again that the commission will approve the new type
species. David Patterson would be a good person to clarify this
possibility.

Hope this is of some help.

Kind regards,

Dan


On Fri, Feb 4, 2011 at 9:58 AM, Karolina Fucikova
<karolina.fucikova at gmail.com> wrote:
> Hello all,
> I am working on a monograph of the algal genus Bracteacoccus and I have come
> across a problem with the type species, B. aggregatus. I am hoping someone
> here could give me some suggestions.
> OK, here goes: The holotype for B. aggregatus is a figure and not a very
> informative one. The circumscription has some usable info but not a lot. The
> generic diagnosis of Bracteacoccus was emended by Starr in 1955. By then,
> the live material (culture) associated with B. aggregatus was not available
> (presumably lost or dead), and Starr based his emendation on another
> species, B. minor. Since then, phycologists have been using Starr's concept
> of Bracteacoccus, and several other species of Bracteacoccus have been
> described since.
> Now, I have molecular data for most Bracteacoccus species (based on type
> cultures), but the most important one is obviously missing - B. aggregatus.
> Not only is there no type material available - there are virtually no
> cultures of B. aggregatus available at all. It's almost like nobody has seen
> that species since its description in 1923. No wonder, too - with the vague
> species description. What can I do about the type for the genus then? I have
> heard of epitypes - I suppose I could pick a Bracteacoccus isolate that
> roughly matches the original description and call it aggregatus, right? But
> does that make sense when the genus name as we use it today is tied to
> characteristics of a different species, B. minor? Is it acceptable for B.
> minor to be designated a lectotype for the genus? We don't even know if the
> original B. aggregatus had the characteristics that are now considered
> diagnostic for Bracteacoccus (i.e., unequal flagellar length in zoospores).
> My personal feeling is that it doesn't make sense to impose the name
> aggregatus on something that may not even be close to the original material
> (we'll never know). But in order to keep the name Bracteacoccus, which is
> commonly used and understood, can we just leave aggregatus behind and select
> a new type for the genus?
> Sorry about the lengthy nature of this post - hope someone can help, or
> perhaps refer me to a previous thread on a similar topic.
> Many thanks!
>
> --
> Karolina Fucikova
> PhD Candidate
> Department of Ecology and Evolutionary Biology, University of Connecticut
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-- 
Daniel Lahr
-------------------------------------------------
PhD candidate
Organismic and Evolutionary Biology
U Massachusetts- Amherst
319 Morrill Science Center, Amherst
Amherst, MA 01003