Son of TarzooAuthor: Wayne Leibel, PhD
Here is a quick review of the discus saga up until now. In last month’s column (TFH March 2007) I reviewed the recent work from the lab of Swedish ichthyologist Sven O. Kullander on the systematic status of discus (Ready, J. S., E. J. G. Ferreira, and S. O. Kullander. 2006. “Discus fishes: mitochondrial DNA evidence for a phylogeographic barrier in the Amazonian genus Symphysodon (Teleostei: Cichlidae).” Journal of Fish Biology 69 (Supplement B): 200–211). In this paper, Kullander and associates suggest that there are (at least) three species, including the “Heckel” discus Symphysodon discus; the brown/blue discus S. aequifasciatus Pellegrin, 1904; and the red-spotted green discus, which they re-describe as S. tarzoo Lyons, 1959. The evidence for this conclusion includes not only the morphological distinctiveness of these latter, western Amazonian discus (non-reticulated red spots on the anal fin and sometimes body), but also the genetic isolation of this western population from the other forms based on DNA sequencing data, in contrast to the apparent shared genetic heritage/interbreeding of central/eastern Amazonian brown and blue discus (and, surprisingly, Heckel discus).
The explorer/fish collector Heiko Bleher recently also advocated a three-species model in his book Bleher’s Discus, Volume 1 (2006, Aquapress, Italy), which I presented in an earlier article (“How Many Discus Species Are There?” TFH December 2006). However, Bleher recognizes the red-spotted green discus as S. aequifasciatus Pellegrin, 1904 and the blue/brown discus as S. haraldi Schultz, 1960. In part the confusion stems from Pellegrin’s (1904) original description of S. aequifasciatus and his failure to designate a holotype (official voucher specimen) for it—the three specimens he had included were two red-spotted greens from Lake Tefé and a single brown discus from Santerém.
In 1959, Earl Lyons published a “description” of a new variety of discus from Leticia, Colombia in his hobby magazine Tropicals (Vol. 4, No. 3), which he called “blue tarzoo” but which clearly from the photos accompanying the article, were red-spotted green discus. Whereas other workers, notably Leonard Schultz (1960), denied the completeness and validity of the Lyons “description,” Kullander accepts it as sufficient, re-describes the species S. tarzoo Lyons, 1959, and designates an already preserved voucher specimen in the INPA (Brazil) collection as the new holotype, or neotype (Ready et al., 2006). Thus, S. aequifasciatus, in his view, becomes restricted to Central/Eastern Amazonian populations of the brown/blue discus.
Resolution of the matter of how many species there are, and what to call them, awaits further study, in particular DNA sequencing now being done on Bleher’s collected material by the internationally known molecular biologist and cichlid molecular systematist Axel Meyer of Germany. This work, according to Bleher (Stolting, K., Salzburger, W., Bleher, H. and A. Meyer, 2006. “Preliminary Revision of the Genus Symphysodon Heckel.” Aqua, Journal of Ichthyology and Aquatic Biology: Special Publication), is expected to be published soon and the results are eagerly awaited. Also, as Ready et al. (2006) have pointed out, and which I will further discus in my next column, the DNA data presented in their paper are limited and subject to some question, and in need of further sampling, both with regard to the number of individuals and populations analyzed, and their choice of genes to be sequenced.
In the rest of this column I will touch on a few of the lingering and controversial aspects of the Ready et al. (2006) study I was unable to address in last month’s column.
The Lyons Description
As previously mentioned, the sufficiency and therefore validity of the Lyons “hobby press” description of the red-spotted green discus has been questioned repeatedly by ichthyologists, most notably L. P. Schultz and W. Burgess, who have both attempted revisions of the genus Symphysodon. Writing in the “Holiday Issue—1960” of Tropicals (Vol. 4, No. 3), Lyons recounts the story of the importation of these fish from Leticia, Colombia to Chicago, including the origin of the name “tarzoo,” attributable to the collector/exporter Mike Tsalickis, co-owner of the Tarpon Zoo in Tarpon Springs, Florida, with a satellite collecting station in Colombia. Lyons writes:
New variety or species? No one knows as yet whether these discus are a new variety or a new species. Their coloring is very different from those which are found near Belém, Paraqua, and Santarém, Brazil—the latter location being over 1200 miles from where this blue discus is found. The name used in this story—Symphysodon Discus Tarzoo—is unofficial, but undoubtedly will be recognized scientifically when the proper authorities have completely examined them.
Lyons continues that the Shedd Aquarium in Chicago had been given six of them, but at the time no conclusion as to their identity had been reached; apparently the assistant curator found them “too beautiful” to pickle. Whereas the cover “photo,” a gaudy, even psychedelic blue-red colorization of a photo of a pair of these fish with the tag line Fabulous “Blue Tarzoo!” are not useful (they look like an Andy Warhol print of a discus), excellent black and white photos of two live fish accompanying the article clearly show what discus hobbyists have subsequently come to call “Tefe green” discus, even if these are from Colombia and not Brazil.
A follow-up article in the very next Tropicals (Winter Issue—1960, Vol. 4, No. 4—thanks to Ray Wetzel for providing the articles) seems to shoot down the possibility of new variety or species status for “blue tarzoo.” The introduction, entitled: “Rediscovered Color Variation—‘Blue Tarzoo’ Classified as Heckel Variety” follows verbatim:
The beautiful “Blue Tarzoo” discus, covered and photographed in our Holiday Issue, 1960, have been examined closely by Robert D. McCord, a very competent biologist, of Valparaiso University, with the discovery that these fish are the color variation known as Symphysodon discus Heckel. The following is the actual report sent by Mr. McCord to numerous scientific journals throughout the country. It should also be added that in a phone conversation Mr. McCord had with Dr. Meyers, of Stanford University [i.e., Dr. George S. Meyers, internationally known ichthyologist—Eds.], on Feb.9, 1960, Dr. Meyers agreed with McCord’s findings.
McCord’s report, “A Color Variation of Symphysodon Discus Rediscovered,” follows and states:
A color variation of Symphysodon discus has been rediscovered recently in the headwaters of the Amazon River near Leticia, Columbia, S.A. An animal importer, Mr. Mike Tsalickis of the Tarpon Zoo, Tarpon Springs, Fla., has recently imported this variety. These fish were sent to Kyle Swegles and Al Wechsler, tropical fish distributors of Chicago, Ill., where they came to the attention of this investigator. At first report this fish was thought to be a new species and had been tentatively named Symphysodon discus tarzoo; however, after careful investigation and examination of 10 specimens, it has been determined beyond doubt this these fish are the same species of Symphysodon discus that were first described by Heckel in 1840. Specimens of this color variation for confirmation of identification were sent to the following noted authorities on South American fish: George S. Meyers, Ph.D., Stanford University’s Natural History Museum, Palo Alto, Calif., and James Boehlke, Ph.D., Philadelphia Academy of Science, Philadelphia, Pa. Respectfully submitted, Robert D. McCord, Biology Department, Valparaiso University, Valparaiso, Indiana. (Footnote: Taxonomic points and photographs used in this identification accompany this report.)
Remember, of course, that Kullander (1986, Ready et al. 2006) reports that only colorational details, and not meristics or morphometrics—which overlap—cleanly separate the nominal species.
In 1960, ichthyologist Leonard P. Schultz of the United States National Museum, in the pages of the June 1960 issue of TFH, took on the challenge of revising discus systematics and taxonomy (“A Review of the Pompadour or Discus Fishes, Genus Symphysodon of South America”). In summary, Schultz recognized two species, S. discus Heckel, 1840 and S. aequifasciata Pellegrin, 1904, the latter with three distinct subspecies which he describes. (Pellegrin, 1904 had originally described aequifasciata as S. discus var. aequifasciata, later changed rightly to S. aequifasciatus by Kullander 1986 in his Peruvian cichlid monograph.) These subspecies included S. aequifasciata aequifasciata (green discus), S. aequifasciata haraldi (blue discus), and S. aequifasciata axelrodi (brown discus). Later, subspecies of S. discus were also described, including S. discus willischwartzi Burgess, 1981. There are some major problems with the Schultz work, including his inability or reluctance to look at the deposited original holotype specimens himself (he based his diagnoses on previously published counts and measurements), the small number of new specimens examined, and the doubtful origin of some of these. Kullander (1986, Cichlid Fishes of the Amazon River drainage of Peru) examined Schultz’s types and found some of the diagnoses (counts) inaccurate. He cites Burgess (1981) who also reviewed discus systematics in this magazine (TFH 29(7) [March 1981]: 32–42) as therein stating: “at least some of the color differences seem to be only in the eye of the beholder and others are apparently influenced by diet and/or environment factors.” Kullander (1986) lumps the three Schultz subspecies as one species, S. aequifasciatus Pellegrin, 1904 and offers a redescription of it. In his view, until this Ready et al. (2006) study proved otherwise, there are only two species.
As it pertains to the issue at hand, Schultz lists S. discus tarzoo Lyons as a synonym of his new S. aequifasciata haraldi (blue discus) and goes on to comment:
When an unknown or new aquarium fish is introduced to aquarium hobbyists and a name is printed such as the one Mr. Earl Lyons introduced for the blue discus, confusion and disagreement among those interested in scientific zoological nomenclature is likely to occur unless the rules of zoological nomenclature are followed. I have shown Dr. Curt Sabrosky the article by Mr. Lyons and he agrees that the name tarzoo does not have nomenclatorial standing because the following two rules were not fulfilled as defined by the International Rules of Zoological Nomenclature and adopted at the 1927 Budapest Congress. (1) After January 1, 1931, the specific name must have been published with a statement in which the author attempted to indicate differentiating characters or with a summary of characters which distinguish the species from other species. (2) The publication of a figure of the species with a scientific name does not meet these requirements. Therefore, I must conclude that Mr. Lyons’ article does not establish any scientific name. To avoid confusion in the future in our Zoological Nomenclature, it seems wise to describe as a new subspecies the blue discus according to the Rules of Zoological Nomenclature.<End>
Schultz goes on to describe his new subspecies appropriately and designate a holotype which he has deposited in the National Museum (though the collection site listed, Benjamin Constant, Brazil, collected by H. R. Axelrod and Harald Schultz, is doubtful according to Bleher and to Kullander ).
Ready et al. (2006) take issue with Schultz’s conclusion regarding the availability of the name S. tarzoo. They conclude that the Lyons’ description was adequate under the same zoological nomenclature rules cited by Schultz and that the name tarzoo is therefore available for use and not a synonym. As previously reported, the Kullander group offer a new, complete redescription of the red-spotted green discus from Western Amazonia, have designated a new type specimen (neotype) in the absence of any preserved material from the initial importation/Lyons description, and have named it S. tarzoo Lyons, 1959. Additionally, since Pellegrin (1904) did not designate a type specimen for S. aequifasciatus, but deposited his three specimens—two greens from Tefé, one brown from Santerém—as syntypes (equal types), Kullander’s group additionally select Pellegrin’s Santerém specimen (brown) as the type (lectotype) of S. aequifasciatus, thus restricting this name to the Central/Eastern species of “aequifasciatus” discus corresponding to the brown/blue discus (Schultz’s S. aequifasciatus axelrodi and S. a. haraldi, respectively).
In Bleher’s (2006) opinion, since Schultz (1960), given the failure of Pellegrin to designate a type specimen, selected Lago Teffé (Tefé) as the type locality for S. aequifasciata aequifasciata, and based his description on 104 specimens collected there, he believes in and advocates use of the species name S. aequifasciatus for the red-spotted green western Amazonian discus and not for the central/eastern Amazonian species. Given Ready et al.’s specific diagnosis of S. tarzoo based on color pattern (which is also obvious from the monochrome photos of living fish in the Lyons article), the Lake Tefé “green” discus are S. tarzoo and not S. aequifasciatus.
Having a copy of the Tropicals magazine at hand, I was curious as to the attribution date of 1959, since the issue bears the description “Holiday Issue—1960 on its cover and along the bottom of the odd-numbered pages of this 34-page magazine. I have scoured the magazine—its articles and advertising—for a reference to 1959 but have been unable to find anything (though some aquarium society events from October and November are clearly recounted). One clue to the date: in Schultz’s (1960) TFH article (which, along with most of the original discus systematic papers are reprinted in full in Bleher’s book), he cites the Lyons’ article correctly as “Holiday issue 1960” but has, in parentheses, the date “November 28, 1959.” Whether that is the actual date of printing, or mailing, or when he received the magazine is not mentioned, or whether he had been in touch with Lyons, the editor of Tropicals, about the actual date of publication, but that apparently is the date that has stuck with the name and honored by Ready et al.: Symphysodon tarzoo Lyons, 1959. Interesting, to say the least.
I know, I know, all this sounds like a lawyer’s argument and debate. Who cares how many discus species there are and who cares what their names are? Bleher and Kullander, for the moment, agree to accept three species. Both lump brown and blue together as one species and as distinct from the Heckel discus and from the green discus. Where they disagree is about what to call them. But this is no small matter and does come down to, well, lawyerly debate and rules. Moreover, the rather limited number of distinct species (some would argue, and have, that discus are a single species of interbreeding geographically/morphologically variable continuous populations—see my December 2006 article) signals something important about the biology of these fish and about the mechanisms of speciation taking place in the Amazonian drainage. As it turns out, the DNA sequencing data has much to say about what is and what is not happening to these fish. Next time, I will summarize what the Ready et al.’s (2006) study suggests about the evolution of these beautiful and interesting aquarium fish.Is your head exploding yet?