Nasal bioluminescence in reindeer, Rangifer tarandus rubens
The discovery in 1939 of a reindeer mutant characterized by a luminescent snout (and popularly known as 'red-nosed') is a neglected chapter in the history of selective breeding. The mutation initially resulted in the young fawn (nicknamed Rudolph) being ostracized, in much the same manner as documented by H. Christian Andersen in his classic account of the so-called 'ugly duckling'1. However, the timely intervention of S. Claus, who breeds reindeer in Russia's Chukotka peninsula, ensured the persistence of the new trait, which has proved navigationally beneficial on a world-wide basis2. Here I show that the precise mechanism for the luminescence in the reindeer Rangifer tarandus rubens is identical to that which causes the glow in railroad worms.
There has been unwarranted confusion about the first record of the red-nosed reindeer. Priority belongs to R. L. May of the Montgomery Ward department store in Chicago, who made the first independent sighting, accompanied by draftsman D. Gillen, who clearly recorded its shining nose in his sketch and printed illustration3 (Fig. 1). The resulting publication was given the widest possible distribution, to such effect that six million copies had been sold by 1946. The fame of the mutant was ensured by the popular, if inaccurate, musical rendition of its discovery by G. Autrey in 1949.
It is now known that selection for the Rudolph mutant by the notoriously secretive Chukotkan herder, S. Claus, actually about came by chance, during a journey across the habitat occupied by the young reindeer4. Claus recognized that nasal bioluminescence presented a significant adaptive advantage in the prevailing meteorological conditions. The records for 25 December 1949 indicate a worldwide fog of unprecedented extent5. Claus' adoption of Rudolph and cultivation of a pure-breeding strain facilitated his navigational tasks during the smogs that beset developed countries in the 1950s and 1960s.
The famous red glow arises from a chemiluminescent reaction involving a direct conversion of chemical energy into light. It involves the substrate d-luciferin combining with ATP and oxygen, in a reaction catalysed by the enzyme luciferase, with light being given off along with the product oxyluciferin. The forms of luciferin and luciferase differ chemically in different organisms6, with the colour of light given off varying according to the substrate, ranging from blue in marine organisms to yellow in fireflies. The mechanism in R. t. rubens is identical to that seen in larva of the beetle Phrixothrix hiatus, known as the railroad worm, which produces red light from its head and green light from its body7.
The size of the current population of Rudolphs is impossible to estimate with any accuracy, but it must run into many millions. There have been proposals to classify the twentieth-century 'red-nosed' subspecies as a pest8. However, a proper understanding of its natural history will almost certainly reveal that natural controls are already beginning to operate effectively.
Competing interests statement The author denies that he has any intention to obtain any financial interest in Rudolph.
I thank A. Abbott for her work on catalysis, which she has shared with me. C. Dawnay provided vital support in helping me obtain PFD funding for this research.