On the Nature and Value of

Scientific Names

Responding to a number of SHARK-L postings which questioned the value and reliability of scientific names, I responded with the following thoughts.

I don't think Tom is giving the scientific community due credit here.

Nature is messy, rarely fitting into the neat categories we try to impose upon her. We humans are very good at recognizing patterns. We are so good at finding patterns that we are able to create order where none may, in fact, exist recall the classic optical illusion consisting of a pattern of irregular black blotches that resolves itself into a quite convincing Dalmatian sniffing at an unseen something on a leaf-strewn footpath (see page 130 of: Rock, I. 1984. Perception. Scientific American Library, W.H. Freeman and Co., New York.). The blotches are not the dog, the map is not the territory, and the individual scientist is not the process of Science.

Scientifically speaking, biological classification serves two main purposes: 1) a basis for generalization in comparative studies and, 2) an information storage system. Linnaean binomial nomenclature is thus merely an expression of current ideas about how this or that organism can be grouped with others, a kind of short-hand that allows taxonomists to discuss a 'work in progress'. The species is the lowest ranking taxon and the only 'natural' one (for the moment, I will sidestep the complicating fact that even experts often do not agree on what, exactly, a species is); all larger taxa are arbitrary and thus subject to change based on new information and how experts interpret their meaning. Ideally, the taxonomic ranking of a given species reflects its phylogenetic interrelationships with other organisms. But this is difficult to do in practice.

Defining species was formerly very straight forward and easy to understand: if two organisms looked alike, they were the same species; if not, they belonged to different species. But it quickly became clear that this simplistic system was inadequate: Linne himself originally classified the male and female Mallard Duck (now known as Anas platyrhynchos) as different species. For sexually reproducing organisms, the so-called 'biological species concept' came into vogue. By this paradigm, a species is a population or series of populations of organisms that freely interbreed with one another in natural conditions to produce viable (capable of reproducing) offspring. By this definition, horses and donkeys are different species, as their offspring a mule or hinny is sterile (incapable of reproducing). This concept is further weakened by the creation in zoos of 'tigrons' or 'ligers', offspring of Tigers (Panthera tigris) and Lions (Panthera leo). [There are those who balk that a zoo is not 'natural', but I think they are arguing from a false dichotomy: the human brain is a biological organ that evolved under biological rules and constraints. Therefore, anything of which the human mind can conceive zoos, Hamlet, Carmen, bank line-ups, Jim Carrey movies, etc. is, ipso facto, 'natural'.] With the development of cladistic phylogenetics, species came to be defined as the smallest group of organisms that displays a given suite of synapomorphous (derived) characters. To a molecular geneticist, a species is the smallest unit that displays a given suite of synapomorphous nucleoprotein sequences. To summarize all this in the most cogent way I can: what a 'species' is depends in part on which method of classification one uses (external morphology, reproductive competence, or codifiable character states with a polarity amenable to cladistic analyses).

In theory, members of a given species are supposed to resemble one another than members of other species. But in the 'messy' Real World, we often find that variation within species is often greater than variation between or among species. It is important, also, to bear in mind that although the fact was not known to Linne species change over time. In trying to define a species, scientists are faced with the difficult task of pinning down a continually moving target.

To return to shark taxonomy: In Linne's time (the late 1700's), only about 11 species of shark were known, and all could be conveniently squeezed into the single genus Squalus. By the 1840's, some 40 species of sharks were known, and a single genus was no longer adequate to express this diversity; by 1900, about 160 species were known. Today, something on the order of 390 species of shark have been formally described and that's not counting some 490 or so batoids. Over the past 250 years, scores of biologists have tried to organize the species of sharks known to them into groups that adequately reflect the diversity and presumed interrelationships of these fishes.


Basking Shark (Cetorhinus maximus)

Consider Tom's example of the Basking Shark, presently known by the formal scientific name Cetorhinus maximus. This species was originally named Squalus maximus in 1765 by Norwegian naturalist and cleric Johan Ernst Gunner, based on a specimen he observed or examined at Trondhjem, Norway. (Gunner, incidentally, was the Bishop of Trondhjem at the time, and even suggested that Jonah was swallowed by this particular type of "great fish" showing once again that it's only human to try squeezing as many things as possible into the conceptual framework that best suits one's present world-view.) Because of this fish's huge size even a 1.7-metre-long newborn Basking Shark does not easily squeeze into a bottle of preservative no holotype (representative specimen) was collected or deposited into the permanent collections of an academic institution to serve as the ultimate reference against which to check similar species. When it became clear that these sharks were fairly abundant, at least seasonally, in European seas, the species was harvested commercially allowing biologists to gain a fuller understanding of its anatomy and growth stages. As human beings ventured ever father out into cold temperate seas of both hemispheres, Basking Sharks that were clearly similar to those known from home waters were encountered. Eventually, small to not-so-small differences were noted among the various populations of Basking Sharks. Siccardi (1960, 1961) suggested that there are four species of basking shark, two from the North Atlantic and Mediterranean (Cetorhinus maximus and C. rostratus), one from southern Australia (C. maccoyi), and one from the South Atlantic (C. normani). In their review of these nominal species of basking sharks, Springer and Gilbert (1976) reasoned that the anatomical differences noted by Siccardi may have been due to allometry (changes associated with growth) in the Basking Shark, and concluded that there is insufficient evidence at present to separate these species. Pending further work on the matter, Compagno (1984) agreed with Springer and Gilbert, synonymizing all nominal species of basking sharks under Cetorhinus maximus. Compagno's tentativeness is a fine example of the caution that is the hallmark of true scholarship. If more comprehensive population studies and molecular genetics can demonstrate that Siccardi's nominal species or perhaps other, as-yet un-named populations of Basking Sharks are sympatric (have overlapping ranges) but do not interbreed (exchange genetic material), they could under the biological species concept be legitimately regarded as discrete species.

In the interests of not prattling on too horribly long, I will refrain from going into the whys and wherefores surrounding taxonomic changes to the Porbeagle Shark (Lamna nasus), but would suggest that the various name-changes of this species had more to do with earlier scientists not understanding allometry in this widespread species rather than incompetence, confusion, or malice on the part of fish taxonomists. (It was, incidentally, not until 1947 that Hubbs and Follet designated a second valid species of Lamna the Salmon Shark, Lamna ditropis.)

As our tools for exploring the natural world continue to be refined and our sensory capabilities thereby extended, we are beginning to appreciate that the biological richness of our planet is much greater than it appeared to earlier explorers. Nowhere is this more obvious than in the sea. Molecular genetic techniques have revolutionized our ability to explore all levels of biological diversity. Small genetic differences may be used to identify species whose morphological differentiation is difficult to see or whose morphology is unknown at one or more critical life history stages. Many long-studied, wide-spread marine organisms including plankton, corals, mussels, polychaetes, crustaceans, fishes, and cetaceans traditionally thought to be single species are now through the power of molecular genetics known to represent several species. These so-called 'cryptic sibling species' have important implications for conservation and management. The commercially valuable mussel Mytylus edulis one of the world's best-known invertebrates is now known to be three distinct species; different growth rates of at least two of these compromise the validity of marine pollution monitoring based on what was thought to be a single species, thereby compromising safety standards for consumption of heavy metal and other pollutants ingested as part of many seafoods. The common Star Coral, Monastrea annularis is now known to be at least three distinct species; each of these has different growth rates and carbon isotope ratios, thus affecting previous estimates of global climate change. In 1986, J.D. Stevens and P.D. Wiley used differences in enzyme systems to differentiate two species of commercially-important northern Australian shark that were previously believed to be identical: the Blacktip Shark, Carcharhinus limbatus and its cryptic sibling species, C. tilstoni. Each of these look-alikes has somewhat different life history parameters that may profoundly affect how each of them responds to similar management or conservation procedures.

Had Stevens and Wiley not had the tools to distinguish these two look-alike sharks, or been persuaded by those favoring the existing status quo to not confuse the nomenclatural situation by erecting a new scientific name to indicate that the commercial fishery is targeting two species rather than one, the long-term survival of both species may have been jeopardized. C. limbatus and C. tilstoni may yet be exterminated but by recognizing their differences by name both of these species' chances for continued survival off northern Australia are significantly improved.

In the vast majority of cases, each and every animal species has only one, unique scientific name. This name is internationally agreed-upon according to rules laid down and moderated by the International Commission on Zoological Nomenclature (ICZN), enabling scientists from every country to exchange information and regardless of what other linguistic hurdles may be encountered to be absolutely certain they are all discussing the same species. The same cannot be claimed for vernacular names. A Blue Shark (Prionace glauca) is not always called a 'blue shark' in English, it has been variously known as a 'blue dog' or a 'blue whaler' to say nothing of its vernacular names in scores of other languages: in Arabic, it's zerica; in Danish, blaahaj; in Dutch, blauwehaai, in French, requin bleu or peau bleu: in German, blauhai; in Italian, verdesca; in Norwegian, blaahai; in Portuguese, tintureira or tintureiro; in Serbo-Croat, zupka; in Spanish, tiburon azul or tintorera; in Swedish, blahaj ... I could go on, but I think I've made my point. Also, application of common names to several distinct and sometimes not even particularly closely related species often occurs. This occurs even in the English language, as in the case of Ginglymostoma cirratum and Nebrius concolor both being called 'nurse sharks'.

So, to sum up: Nature is messy, Science is tentative; as long as these truths remain relevant to biological research, scientific names will continue to be revised. Scientific names are never changed capriciously or maliciously; they are provoked by inconsistencies between old and new data and changed (often reluctantly) on the grounds of sound scientific reasoning. Tom and others frustrated by the apparently perpetual game of 'scientific name catch-up' may take some comfort in the fact that as criteria for defining species become more rigorous and tools for differentiating species and determining evolutionary relatedness become ever more refined changes to scientific names will become increasingly rare.

Apologies for building such an overwhelming case, but as you can probably tell I'm rather passionate about all this. As Confucius put it, "The beginning of wisdom is to call things by their right name."

If any list-users want to help clear up some of the confusion about scientific names, may I suggest you support your local taxonomist.

Cheers,

     R. Aidan Martin

[Posted to SHARK-L March 8, 1998]

 

ReefQuest Centre for Shark Research
Text and illustrations R. Aidan Martin
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