Albino Zebras and Leopards Changing their Spots

Zebra Shark (Stegostoma varium), showing typical pigmentation pattern of non-albino adult

Responding to a query, " Could someone please tell me if it's true there have been reported albino zebra sharks (Stegostoma fasciata)? And, if so, how do they look like? Are the stripes and then the spots lighter or just gone? What about the eyes, are they red?", I wrote:

In 1973, Nakaya reported a partial albino of Stegostoma varium (= fasciatum) taken from the Indian Ocean during January of 1964 (Jap.J.Ichthyol., 20[2]: 120-122). The specimen was a mature female, 185 centimetres long, having a uniformly white body with a very slight red tint (blood/blood vessels near the surface of the body and visible through the translucent skin?); it lacked all traces of the black spots or blotches usually present in adults of this species, but the fin margins were greyish. The irises of this specimen were blackish-brown, much as in normally pigmented individuals of this species, leading Nakaya to suggest it was a partial albino. Nakaya notes it is interesting this specimen had grown as large as it had, suggesting that a very pale shark would be quite conspicuous against a darker bottom and perhaps be more vulnerable to predation.

. . . are there any noticeable behavioural - courtship/reproductive success- differences?

Unknown.

In true albinism, epistatic genes block expression of the gene coding for tyrosinase, the first of a series of enzymes needed to produce pigmentation. Without tyrosinase, no pigment whatever can form. At least six other epistatic blocks can occur along the conversion route. If they occur at later steps, slight amounts of pigment still form and imparts some color to the individual (as in Nakaya's partial albino Stegostoma).

There may be a link between tyrosine (which is acted upon by tyrosinase) and aggression, which - in turn - may have implications for breeding behavior and, ultimately, for reproductive success in vertebrates. An alternative pleitropic pathway leading to the production of certain monoamines results in neurotransmitters which control motivational systems in the vertebrate brain. Therefore, a gene acting on a pathway leading to tyrosine might influence simultaneously *both* body color and aggressive behavior. A polymorphism is known in birds in which these traits vary concordantly. For example, in a European bird known as the Ruff (Philomachus pugnax), the melanistic form is more aggressive than and dominant over the lighter form. The possibility exists that the social organization on the lek of the Ruff has been influenced by a mutation in the tyrosine pathway.

Thus albino or other pale color morphs of sharks - particularly in males - may reduce assertiveness during courtship and reduce the likelihood of successful mating in such individuals.

Also, whale sharks do keep the exact same marks they're born with all their lives. Right?

Probably, but this has not been verified experimentally. Tagging of Whale Sharks is a relatively recent activity and no one - to my knowledge, at least - has tagged a neonate of this species and observed its pigmentation pattern for changes throughout its lifetime (however long that might be - 25 years?).

Leopard Shark (Triakis semifasciata)

If you remember any piece of curious information about Leopard Sharks (Triakis semifasciata)

Off the top of my head:

• a true albino of Triakis semifasciata has been reported, lacking all traces of the dark spots and saddles typical of this species and complete with pink irises
• off California, adults of this species regularly feed on echiuran Innkeeper Worms (Urechis caupo), actually sucking them from their U-shaped burrows in the mud and swallowing them whole
• Leopard Sharks sometimes mutilate their prey, consuming only a part of them - such as seizing the extended siphons of buried clams and ripping them off with violent lateral head-shaking; it is not uncommon to find dozens of fleshy bivalve siphons (no bivalves, just the siphons) in stomachs of these sharks
• although generally regarded as harmless, there is a report of a leopard shark charging a skin diver with a nosebleed

Another voice added: " are there parts of the world where they refer to zebra sharks as leopard sharks, or vice versa?

Both names are correct, although one has advantages over the other and is thus preferentially used.

Juvenile Stegostoma varium (= fasciatum) - less than 50 cm long - sport a striking pigmentation pattern, consisting of chocolate brown back and flanks broken into irregular saddles by thin yellowish vertical bars and spots extending upward from the pale yellow belly and the tail is similarly marked. At this life history stage, the animal is well described by the common name 'zebra shark'. Between lengths of about 50 and 90 cm, however, zebra sharks' saddles break up into small brown spots and faint brownish splodges on a yellowish background, the markings becoming less linear and the spots more uniformly distributed with growth. Although there is considerable variation in the precise pigmentation pattern among individuals of this species, by the time zebra sharks are adult, their back and flanks are pale yellow to yellowish-brown sprinkled with small dark brown to black spots. At this life history stage, the name 'zebra' seems downright inappropriate and the species is often referred to as by the more descriptive name, 'leopard shark'.

Although vernacular names are not governed by the sort of stringent rules which constrain scientific binomia, it is a general tradition that the common name of an organism describes the adult rather than the juvenile phase (hence, to cite two piscine examples, the names Bluehead Wrasse and Blue Tang are used for Thalassoma bifasciatum and Acanthurus coeruleus, respectively, both of which are bright yellow as juveniles). But there is a boldly saddled and spotted but unrelated smoothhound of the family Triakidae (Triakis semifasciata) which is also widely known as the leopard shark; in addition, the name 'leopard shark' has in the past been fairly widely used for the Tiger Shark (Galeocerdo cuvier) of the family Carcharhinidae.

So, to avoid confusion, the unique name 'Zebra Shark' became preferentially used for Stegostoma varium (= fasciatum).

... I hope the above is of some help.

Cheers,

     -- R. Aidan Martin

[Posted to SHARK-L July 27, 1998]

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The Zebra Shark - What's in a Name

No, the genus Stegostoma seems to be monotypical (represented by a single species).

One of the fundamental rules about the establishment of scientific names is that the earliest proposed binomen (two-part name, composed of a paired genus and species) that is accompanied by a formal description (detailing precisely how the purported new species differs from all similar species -- preferably buttressed by the designation of a curated 'holotype', or representative specimen, which thereafter serves as the ultimate standard for comparison). But, as with many other rules, there are exceptions. For historical reasons (about which more later), 1758 is the arbitrary cut-off date for scientific names, and no name proposed before that date will be considered. Sometimes, however -- due to logistical hurdles, such as publication in an obscure journal that has been largely overlooked by taxonomists -- the earliest valid name is not discovered until long after a younger name has attained widespread use. In such cases, the International Commission on Zoological Nomenclature (ICZN) -- of which I have previously written -- will exercise its plenary powers to formally suppress an older, largely unused but otherwise valid name and declare the younger but widely-used name as the binomen to be preferentially used by taxonomists.

For example, most of us know the Oceanic Whitetip Shark as Carcharhinus longimanus. This species was named Squalus longimanus by Poey in 1861, based on a 164-cm male specimen from Cuba. ( This species has been placed in various genera over the years -- most notably Pterolamiops, proposed by Springer in 1950, but was first placed in its current genus by Garman in 1881, under the name Carcharhinus obtusus, which was formally reinstated as the preferred genus by Garrick in 1982, who advocated the now-familiar name, Carcharhinus longimanus.) But, it turns out, that the same species had already been described as Squalus maou by Lesson in 1830, based on two specimens about 122 cm in standard length (straight line distance from the tip of the snout to the upper precaudal pit) from the Paumoto Archipelago (now better known as the Tuamotu Archipelago, in French Polynesia). No holotype was designated, but Lesson did provide an unmistakable illustration of his purported new species -- in the widely-available Reader's Digest book, Sharks: Silent Hunters of the Deep (on the lower left of page 68), you can check out a full-color reprint of the original illustration that accompanied Lesson's description. The drawing, done by an artist (whose name I have not yet been able to discover) on board Duperrey's 1822--1825 Pacific voyage on the Royal French Corvette Coquille, is rather stylized (as was common in natural history illustrations of the time) but clearly represents a small male Oceanic Whitetip. Yet Lesson's description, published in French as part of the zoological account of the voyage of the Coquille, lay buried and largely unnoticed among the book's 471 pages. From his 1982 revision of the genus Carcharhinus, Garrick was clearly aware of Lesson's description and accompanying illustration, but -- in the interests of taxonomic stability -- opted to retain the more-familiar and widely-in-use name longimanus in favor of the older, valid-but-obscure name, maou. This has been followed by Compagno in his 1984 FAO catalogue, Sharks of the World, and subsequently by most ichthyologists and shark enthusiasts (myself included -- for practical as well as poetic reasons: longimanus means "long hands", which nicely describes the paddle-like pectoral fins of this species; maou is simply derived from a local word for "shark"). But until the ICZN makes a formal ruling on this matter, technically, Carcharhinus maou (Lesson) 1830 is the oldest valid name for the Oceanic Whitetip and the name which has priority.

And so, having established the relevant theoretical framework, on to the Stegostoma issue which prompted your inquiry.

At first glace, it doesn't make a lot of sense to call a spotted shark "zebra".  But the Zebra Shark (Stegostoma varium) starts out life sporting strongly contrasting bars of black and yellowish-white.  As the shark ages, these bars break up into linear patterns of spots.  These spots, in turn, break up into the leopard-like pattern seen here. Photo © Jeremy Stafford-Deitsch; used with the gracious permission of the photographer, who asks that you support the Shark Trust.

As far as taxonomic scholars can tell, the Zebra Shark was first described by Seba in 1758 as Squalus varius, probably based on specimens from Indonesia. Seba's description (in Latin) is comprehensive and accurate, and -- although no holotype was designated -- is supported by a good illustration of a juvenile (with a caption in French). This species was placed in the genus Stegostoma by Müller and Henle in 1837, under the name fasciatus, following yet another pair of taxonomists, Bloch and Schneider, based on their standard text of 1801. Compagno (1984) followed Müller & Henle in adopting Stegostoma as the genus for the Zebra Shark, but rejected the species name varius, on the grounds that Seba's nomenclature was not consistently binomial, preferring to use the next-oldest species name fasciatum, based on Herman 1783. The classificatory scheme used by all modern biologists is based on one originally proposed by botanist Linne (Linnaeus) in the 10th edition of his Systema Naturae, published in 1758. Latin names had been used long before then, but they were highly variable in structure (ranging from a single word to long, complex descriptive sentences or paragraphs); in 1758, Linne changed all that when he formally proposed the binomial system of nomenclature, a standardization which was quickly adopted by the scientific community. In honor of this achievement, 1758 remains the arbitrary cut-off date for the earliest acceptable binomial. As acclaimed ichthyologist Randall points out in his excellent 1986 book, Sharks of Arabia (p 70), even if many Seba names are non-binomial, his Squalus varius most definitely is. As a result, Randall adopts the name Stegostoma varium for the Zebra Shark. (In case you're wondering, varium is the preferred Latin form of for the species name in this case, as ICZN rules dictate that species epithets used as adjectives in the nominitive singular must agree in gender with the generic name.* ) In any event, Randall's reasoning makes perfectly good sense to me, and -- since Seba's description and illustration are unambiguous, his name does not violate the 1758 cut-off date, and the name varius ("variable") nicely reflects the dramatic pigmentation and proportional changes this species undergoes as it matures [while fasciatum ("banded") reflects only the juvenile phase] -- for the Zebra Shark, I prefer to use the name Stegostoma varium .

As Confucius reputedly once put it, "The beginning of wisdom is to call things by their right name". But it is well to bear in mind that using the 'correct' name is merely a beginning. It's what you do with this knowledge that counts.

In any case, I hope this helps.

Cheers,

     -- R. Aidan Martin

[Posted to SHARK-L January 31, 1999]

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