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February 9, 2015

 

Why Are You Still Saying “Litopenaeus” vannamei?

 

In a 1997 book, Penaeoid and Sergestoid Shrimps and Prawns of the World (Keys and Diagnoses for the Families and Genera), Dr. Isabel Pérez Farfante (deceased) and Dr. Brian Kensley (deceased) proposed some changes in the way scientists refer to the popular farmed shrimp species, and those changes were generally accepted by scientists worldwide.  Except for the giant tiger shrimp, Penaeus monodon, which got to keep the “Penaeus” title, all the other popular farmed species had to add a few syllables to their genus name (the first half of the scientific name).  Good old Penaeus vannamei became Litopenaeus vannamei.  And there were similar changes for stylirostris, indicus, chinensis, japonicus and several other farmed species.

 

Most scientists, journal editors and aquaculture publications quickly adopted the name changes suggested by Pérez Farfante and Kensley; however, there were a few scientist and participants in the shrimp farming industry that did not go along with the name change.

 

At the time of the proposed name changes, Dan Fegan, the owner and editor of The Shrimp List, who currently works for Cargill aquaculture feeds in Asia, said: “The acceptance of the promotion of the subgenera of penaeid shrimp to the  genus level by Perez and Kensley (1997) is not universally accepted and the  revision has not yet been accepted by the International Commission for  Taxonomy and Nomenclature.  No one is obliged to follow the new taxonomy for generic names (as opposed to species names where, if a name is adequately described according to the accepted rules, it must be accepted).  Only if a taxonomist considers a new species description to be inadequate may he/she appeal to the International Commission.  If they do not accept the genus under which the new species has been included, they are not obliged to do so.  What this means is that species have to be recognized, but higher taxa, including genera do not.  Soooo...I'll be sticking to Penaeus in the future.  I'm too old to change and remember all of the new names.”

 

 

At the time of the proposed name changes, Jeff Peterson, who decades ago farmed catfish and then shrimp and currently works as a quality control specialist for the Global Aquaculture Alliance, said: “I support sticking with Penaeus vannamei.  In the ongoing battle between the taxonomic lumpers and splitters I'm a lumper kind of guy.”

 

Even Dr. Donald Lightner, the famed shrimp pathologist at the University of Arizona in the United States, continued to use Penaeus vannamei until a few years ago.

 

Then, in the April 6, 2007, issue of the journal Aquaculture, a review article written by Dr. T.W. Flegel, a professor at Mahidol University in Thailand, said it’s okay to drop the “Lito” from Litopenaeus and use Penaeus vannamei again!  In fact, Aquaculture, the most prestigious of the fish and shellfish farming journals, encouraged it!

 

In his review article in Aquaculture, Dr. Flegel said: "Due to general unfamiliarity regarding the rules of zoological nomenclature, non-specialists in the shrimp industry and even scientists in related academic fields felt that they were obliged by taxonomic rules to follow the changes embodied in the monograph, whether they agreed with them or not.  Others more familiar with their rights (including myself) continued to use the traditional binomials.  The result has been some confusion in shrimp nomenclature in the succeeding nine years.  The purpose of this review is to argue that the revisions embodied in the Pérez Farfante and Kensley monograph are extremely disruptive to communication amongst practitioners in the shrimp fishery and the shrimp aquaculture industry and to scientists and students who study shrimp.  This feature alone is counter to the goal of stability embodied in the zoological code of nomenclature and can alone be sufficient justification to consider the proposed revisions unacceptable.  Indeed, the success of proposed taxonomic revisions does not fall under the zoological code, since the code is concerned with issues of priority.  Instead, revisions survive or die depending on the majority action of the whole impacted community acting as individuals to accept them by use or reject them by disuse.  Apart from arguments based on nomenclatural stability, I will attempt to show that sufficient new genetic information on penaeid shrimp has been accumulated in the past nine years to show that there is no compelling reason to accept the revisions."

 

“No one is obliged by the rules of zoological nomenclature to accept the revisions in penaeid shrimp binomials proposed by Pérez Farfante and Kensley (1997). Given the potential disruptive effect of the proposed changes in scientific communication and trade, I believe that very strong arguments should have been put forward as to why the changes were technically and practically necessary. This should have involved a discussion of all the issues as they might impact on the shrimp fishery and the shrimp culture industry. Ideally in such situations, all those impacted should listen to one another, recognize and respect other points of view and thereby gain a broader appreciation of systematics and of the whole range of different attitudes held by colleagues around the world.”

“I recommend that authors who are pressured by journal editors to adhere to the proposed Pérez Farfante and Kensley (1997) revisions against their will and as a requirement for publication withdraw their article and submit it to a different journal that has an unbiased and non-coercive editorial policy.”

In his Acknowledgements at the end of the review, Flegel said: "I would like to thank Dr. William 'Bill' Dall formerly with the Queensland Museum and CSIRO Australia for the inspiration to write this article and for his valuable comments and encouragement during its preparation."


Aquaculture not only placed Flegel's article at the very beginning of the April 2007 issue of its journal, it preceded it with an editorial in favor of the name change, saying: We wish to draw your attention to a paper by T.W. Flegel entitled "The right to refuse revision in the genus Penaeus". ...We are in agreement with the arguments put forward in T.W. Flegel's paper and have agreed that Aquaculture prefers submissions on penaeid shrimp use the generic epithet Penaeus, preferably qualified at the first mention by Flegel's proposal, namely to follow the rules of zoological nomenclature by placing the subgenus names in brackets between the traditional genus name Penaeus and the relevant species name at first mention [e.g., Penaeus (Fenneropenaeus) chinensis]. The editors do not however wish to be "coercive" in this matter and so authors who feel strongly supportive of the revised Pérez Farfante and Kensley (1997) generic names should use Flegel's alternative at the first mention of the genus to indicate that another name is also used [e.g., Fenneropenaeus chinensis (also called Penaeus chinensis)].

 

The Final Blow to Litopenaeus

 

The final blow to Litopenaeus should have come with the publication of “Refuting the Six-Genus Classification of Penaeus s.l. [sensu lato, meaning ‘in the broad sense’] (Dendrobranchiata, Penaeidae): A Combined Analysis of Mitochondrial and Nuclear Genes” by Ka  Yan  Ma, Tin-Yam  Chan and Ka  Hou  Chu (email kahouchu@cuhk.edu.hk, Simon F. S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong).  Zoologica Scripta, Volume 40, Issue 5, Pages 498–508, September 2011.

 

The study provides solid morphological and genetic information on why the name change should never have been made, but even thought it was published over three years ago, it has had little effect on the way scientists and others refer to the penaeids.

 

 

Here Are Some Quotes from the Study

 

“The suppressing of genera or subgenera in Penaeus s.l. (or, in other words, restoring the old Penaeus genus = Penaeus s.l. [sensu lato, meaning ‘in the broad sense’]) is deemed most appropriate for the current state, for two reasons.  Firstly, the morphological and molecular data are in agreement under this scheme.  Because molecular data from both the mitochondrial and nuclear genomes strongly suggest that Penaeus s.l. is monophyletic, the only scheme in which the current morphological predictions concur with molecular data is the Penaeus s.l. concept.  Secondly, given that the six-genus scheme has been found to be invalid, restoring the old Penaeus genus would cause less confusion to users than proposing a newly defined two-genus or three-genus scheme as discussed previously.  Speaking on behalf of the stakeholders on the issue of Penaeus s.l. taxonomy, Flegel (2008) suggested that the most disruptive option would be ‘to discard the original genus concept or to more narrowly define it, and then to propose a number of new genera…’, whereas the least disruptive decision would be to ‘preserve the old genus concept’.  Although such lumping of taxa would create a species-rich Penaeus genus with high intrageneric genetic and morphological differences, this case is not matchless.  Among crustaceans, the freshwater crayfish Cherax (with 34 species, De Grave et al. 2009), the shrimp Metapenaeopsis (74 species, De Grave et al. 2009) and the squat lobster Munida (246 species, De Grave et al. 2009) also contain lineages with genetic divergence comparable with or even higher than that shown in Penaeus s.l. (see Tong et al. 2000; Munasinghe et al. 2004; Cabezas et al. 2008, 2009), but these genera are not split into smaller taxonomic units.”

 

“To sum up, in terms of both scientific evidence and constructing a workable classification scheme, here we find that reinstating the old Penaeus genus and dismissing the six genera/subgenera are deemed most justifiable, at least for the time being. We recommend that only when some morphological characters can be mapped to the molecular phylogenetic tree should the genus Penaeus be formally subdivided.”

 

 

Here is the Study’s Abstract

 

"The taxonomic revision in 1997 of the shrimps formerly classified in Penaeus s.l. has been one of the most controversial issues on systematics of the decapods in recent years.  Since Pérez Farfante and Kensley (Penaeoid and Sergestoid Shrimps and Prawns of the World, 1997) split this long-accepted taxon into six genera, much debate has been devoted to their proposed new classification scheme; this has taken place because there are serious doubts whether the said scheme could reflect the evolutionary relationships among the 29 Penaeus s.l. species.  Although these shrimps can be easily separated into several groups morphologically, whether these subdivisions are truly monophyletic and warrant a generic rank continues to be hotly debated among taxonomists.  This study examined a total of 2425 bp sequences from three nuclear protein genes (enolase, phosphoenolpyruvate carboxykinase and sodium–potassium ATPase a-subunit), and the mitochondrial 16S and 12S rRNA gene of 18 Penaeus s.l. shrimps and 13 other species in the family Penaeidae.  Our phylogenetic analyses strongly support the monophyly of Penaeus s.l. and, concurring with previous studies that used the mitochondrial genes alone, the paraphyly of both Penaeus s.s. (sensu Pérez Farfante and Kensley, Penaeoid and Sergestoid Shrimps and Prawns of the World, 1997) and Melicertus, rendering them non-natural groupings.  Our study reveals two  lineages: Penaeus s.s. + Fenneropenaeus + Litopenaeus + Farfantepenaeus and Melicertus + Marsupenaeus, which exhibit genetic divergences comparable with those among other penaeid genera.  However, all the morphological characters, which are emphasized by Pérez Farfante and Kensley and used to separate Penaeus s.l., do not correlate with the grouping revealed by the present, perhaps decisive, phylogenetic result.  Such disparity may arise from selection on the morphology of genitalia and convergent evolution.

 

Our  molecular data clearly refute the six-genus classification, and we advocate the restoration of the old Penaeus genus (= Penaeus s.l.) definition which is the only classification scheme with both the morphological and the molecular data being in agreement."

 

 

Updates

 

In an email to Dan Fegan on October 3, 2014, Professor Flegel wrote:

 

"With respect to any future changes in taxonomy that might be proposed, my opinion is that they be confined to the sub-genus category.  That level of classification would be sufficient to indicate genetic sub-relationships in the genus Penaeus without disturbing links to the previous literature, without requiring any name changes in regulations and without causing any economic problems (e.g., the need to change package labeling) in this very important industry."

 

In an email to Shrimp News on February 9, 2015, Professor Flegel wrote:

 

“In response to a recent inquiry about the Penaeus versus new genus names, I did a quick search for new information and found the attached paper (above). They show clearly that the 6-genus scheme is not tenable but indicate that there may be some support for dividing the genus into two new gerera instead of 6.  That has been the conclusion of other molecular studies too.  However, at the end of the paper, they say there is precedence from other crustacean groups of similar or wider diversity for keeping to a single genus and in their final sentence they state, ‘We recommend that only when some morphological characters can be mapped to the molecular phylogenetic tree should the genus Penaeus be formally subdivided’."

 

"I think I will start all my future lectures with a reference to this paper and its recommendations.  I'm glad someone finally did some more detailed work including nuclear genes in addition to mitochondrial genes."

 

Information: Professor Timothy William Flegel, Center of Excellence for Shrimp Molecular Biology and Biotechnology (Centex Shrimp) Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400 Thailand (phone 66-2-201-5876, fax 66-2-354-7344, email tim.flegel@gmail.com, webpage http://www.sc.mahidol.ac.th/scbt/academics/research_areas/tf_homepage.htm).

 

 

So—Why Do You Continue to Say “Litopenaeus”?

 

Source: Bob Rosenberry, Shrimp News International, February 9, 2015.

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