Krobia or Aequidens?

[Willem Heijns]

In his description of Krobia xinguensis Kullander (2012) states that "inclusion of A.potaroensis and A.paloemeuensis in the catch-all genus Aequidens best reflects current knowledge". So what is this current knowledge?

In the same paper Kullander argues that the following characters tie the two species to Aequidens:
-naked vertical fins (although the diagnosis for Krobia also allows for naked vertical fins)
-reduced number of vertical bars
-lateral band running to the caudal fin
-predorsal squamation triserial (only in potaroensis).

Characters of the two species shared with Krobia are:
-low vertebral count
-presence of facial stripes
-wide suborbital stripe
-lower E1 scale count
-predorsal squamation uniserial (only in paloemeuensis).

In addtion Kullander says a hyoid furrow (present in most Aequidens species) is absent in the two species at hand.

Musilová et al. (2008,2009) performed a phylogenetic analysis including our two species, the result of which clearly puts them in a clade with Krobia. Kullander critisizes this result by saying that in their morphological analysis 49 out of 96 characters were unknown for our two species and 1 was inapplicable. But that still leaves 46 characters informative for the analysis, which results in the placement of potaroensis and paloemeuensis within Krobia, as does the molecular analysis and the combined analysis.

Considering the above summary of "current knowledge", to which genus would you assign potaroensis? And paloemeuensis?

[Bojan Dolenc]

...
Considering the above summary of "current knowledge", to which genus would you assign potaroensis? And paloemeuensis?

Krobia.
Why is this ichthyologist so angrily trying to nullify the efforts of colleagues?

Question for the experts here: does anyone know, if it is really so?: "in fact, we have probably never seen the "real" Krobia itanyi because this fish is known only from the Marowijne drainage in Surinam (described first by Puyo 1943 from the Rio Itany in French Guiana), far from commercial collecting sites. Instead, the hobby "itanyi" is most likely Krobia guianensis, Regan, 1905, whose extended range throughout the Guianas makes it a reasonable candidate for the collectors' nets, particularly those in Guyana."

[Willem Heijns]

@Bojan: The itanyi issue would be worth a new topic.

[Bojan Dolenc]

Also just that about those 2 species of Krobia:
Species of Krobia are readily distinguished from the other genera in that group by the possession of a dark blotch positioned dorsally on the base of the caudal fin.

Krobia - Aequidens potaroensis


Krobia - Aequidens paloemeuensis

[cichla]

Hi all, interesting topic. Just a small note... The photo (above) shows neither a Krobia potaroensis nor an Aequidens potaroensis, but a Cichlasoma.

[Bojan Dolenc]

Thank You, cichla, Uncle Google has again lied me

Look here, this is I hope real potaroensis
http://www.lem.net/alf/css-krobia.htm#potaroensis

[cichla]

Dear Willem, dear all,
From a phylogentic point of view the current knowledge is best reflected by labeling potaroensis as Krobia (as it is evidenced by the analyses published by Musilová et al. 2008, 2009).

However, in the current use of the zoological systematics there are two different issues. On the one hand (1) the genus name should reflects the phylogenetic relationships and on the other hand (2) a member of the genus have to fit the genus diagnosis.

I guess Kullander is talking about the later one (2). Musilová et al. (2008, 2009) do not re-diagnosed Krobia, and potaroensis does not fit the diagnosis given by Kullander & Nijssen (1989). Thus, in a strict taxonomic point of view potaroensis is formally still an Aequidens.

btw: To prevent change of the genus names (after every new phylogenetic analysis) and to overcome the ambivalence between the requirements (1) and (2) the proponents of the ''Phylo Code'' (an alternative project to the ICZN) recommend not to use (or at least not to change) the genus name anymore.

I think, the best choice (according to the phylogenetic position) is to call it Krobia potaroensis. Anyway, the 'catch all' genus Aequidens will be split soon (papers are on their way) and thus it does not makes much sense to keep it in Aequidens.
Greetings, IS

Why is this ichthyologist so angrily trying to nullify the efforts of colleagues?

To quote Ernst Mayr (1997), the Darwin of the 20th century and founder of modern zoological systematics: ''Some factors that work against acceptance of new ideas are not strictly scientific. Perhaps one author was disliked or had even offended the current Establishment, while another had unexpected success with a subsequently refuted theory because he belonged to a powerful clique.''

[Rico Morgenstern]

Since the express objective of Kullander's 2012 paper was just to formally name a long known species rather than a revision of the genus Krobia, I can follow his reasoning insofar as no revised generic diagnosis, nor a discussion of the characters which led Kullander & Nijssen (1989) to exclude the species from Krobia, is offered by Musilova & al. (although the same measure must then be applied to the largely unexplained name changes and other novelties presented by him in CLOFFSCA, even if this was only a compilation rather than a revision). Musilova & al. have just made a name change according to tree topology. As I would conclude from several previous discussions here and alsewhere, this is a procedure we strongly dislike, at least when the results are not in accordance with our gut feeling, don't we? On the other hand, Musilova & al. offer a quite comprehensive analysis (even if the datasets are incomplete), and the results regarding the species composition of Krobia are consistent. This is deceidedly not a phylogenetic paper of the sort "I have downloaded some sequences from GeneBank (to hell with correct identifications of species!) and added a few new ones - Voilá, here is a sensational new classification"

According to the diagnoses of Krobia (Kullander & Nijssen 1989) and Aequidens (Kullander 1986), the paloemeuensis and potaroensis could be placed in neither genus. Technically speaking, they occupy an intermediate position between these genera. It was perhaps the more vague diagnosis of Aequidens or the weight given to characters shared between Krobia and other genera (e. g. Bujurquina) that led Kullander to override the definition of Aequidens rather than that of Krobia. However, the results of Musilova & al. could well be taken as a decision guidance in favor of Krobia, especially when the generic placement is supposed to reflect "current knowledge".

Some of the characters differenciating Krobia from "Aequidens" are rather vague. The number of vertical bars behind the lateral spot is variable at least in A. paloemeuensis and Krobia sp. "Red Eye", and the course of the lateral band is difficult to assess in some species or at least specimens of Krobia, see e.g. the neotype of K. itanyi in Kullander & Nijssen (1989) (which, by the way, does not correspond very well in this respect with the fishes identified as K. itanyi in the hobby), where the band takes a decidedly straigt course, well separated from the upper lateral line. Life specimens which agree in this respect with the neotype have been figured by W. Staeck (DCG-Informationen 29, no. 9, 1998).

[Willem Heijns]

My guess would be that the PhyloCode project is just about dead. Their website hasn't been updated since early 2010; the last entries in the forum are from 2008 and the forum has been hacked. Anyway, not using the generic name would lead to many "doubles" and never changing a generic name would disregard one of the principles of binomial nomenclature, where the generic name indicates a certain grouping (in the past based on similarities, nowadays more and more based on phylogenetic relationships).

From a philosophical standpoint, the issue at hand is really interesting. We have a phylogeny, clearly saying the species at hand belong in a clade which should be called Krobia. We also have two diagnoses (Aequidens: Kullander 1986 and Krobia: Kullander & Nijssen 1989) none of which our two species seem to fit in.

I should point out here, that generic assignments are a matter of opinion. There are no rules. Assigning species to genera should be done using arguments (i.e. characters) uniting the species with the genus to which it is to be assigned. This is usually done taking into account the diagnosis of the genus. But the diagnosis of a genus is not always stable. Aequidens has always been diagnosed rather vaguely. But who is to say that the diagnosis by Kullander (1986) is the final (and correct) one?

The species paloemeuensis and potaroensis don't seem to fit any of the two generic diagnoses. Should they therefore be placed in a new "intermediate" genus? Or should we change the diagnosis of one (or both) of the genera to make them fit?

In other words: which field is leading: phylogeny? or taxonomy? An interesting issue indeed.

[cichla]

Dear Willem, Dear all,

I do not think that PhyloCode is dead. Papers which attribute to the methods and rules of it are appearing regularly. The desire to create new name is insatiable. Every clade get its own 'genus' name. Often authors not even watch whether a name for the clade is already available or not.

The species paloemeuensis and potaroensis don't seem to fit any of the two generic diagnoses. Should they therefore be placed in a new "intermediate" genus? Or should we change the diagnosis of one (or both) of the genera to make them fit?

Mayr(1991): Taxonomic literature would have been spared countless generic synonyms if taxonomists had always remembered Linnaeus's dictum 'It is the genus that gives the characters, and not the characters that make the genus'

In other words: which field is leading: phylogeny? or taxonomy?

The best method for classification which includes both issues (phylogeny and taxonomy) is the 'evolutionary classification'. It includes also the 'evolutionary distance' and not only the 'phenetic' dissimilarities. However, using this method it is not possible to create many new genera, and hence it is not in vogue.

Greetings, IS

[Willem Heijns]

Ingo,

It's a pity no other members of this forum step into this type of discussion, except you and Rico.

You say PhyloCode is not dead. But I haven't seen any recent publications and their website is ever so quiet.

Also, I'm not sure I understand your Mayr quote, considering that genera are human constructs created to group species which share a set of characters. Or am I missing something?

[cichla]

Willem,
well, I do not know if the internet page of the PhyloCode is dead, but what I know is that there are currently published papers (although not explicitly mentioned) adopting the principles of it. Anyway, we need to be aware that classification (systematics) and nomenclature are actually two different things.
The ICZN uses the concepts of a type species and an explicit diagnosis to name and classify a taxon to a particular rank in the Linnean hierarchy. The PhyloCode, however, uses phylogenetic definitions for supraspecific taxa at any hierarchical level. This is why you may find phrases like 'Definition node-based' instead of a diagnosis for a new taxon in such papers.
The Linnaeus's dictum (see above) would be helpful to prevent countless unnecessary genera names. For example, a genus let it be 'Agenus' is diagnosed by 4 anal fin spines. Later a species is discovered with 3 anal fin spines. Then there are two possibilities: to re-diagnose genus 'Agenus' to having 3 – 4 anal fin spines, or to create a new genus 'Bgenus' differentiate by having 3 instead of 4 anal fin spines.
Greetings, IS

[Willem Heijns]

OK, let's leave the PhyloCode for what it is....

I agree with your analysis of the "changing" diagnoses, Ingo. But what would you do in the case of potaroensis/paloemeuensis?

[cichla]

Since potaroensis is phylogemnetically more closely related to the type species of Krobia than xinguensis (see Musilová et al. 2008, 2009) the best choice would be to re-diagnose Krobia. Otherwise it would end up in having three separate genera for xinguensis, potaroensis and the Krobia sensu stricto.

[cichla]

I just like to note that I am embracing 'nothing', but I think it is a case of believing in authority or trusting in evidence.

[Willem Heijns]

I would put my trust in authorities who give the evidence.