This Week's Citation Classic: Red-Nosed Reindeer

This week's citation classic comes is Halvorsen, O. 1986. Epidemiology of reindeer parasites, Parasitology Today 2: 334-339.

Odd Halvorsen asks "Every Christmas we sing about Rudolph the red-nosed Reindeer, but do we give much thought to why his nose is red?"

Not to my knowledge. Halvorsen has identified a key question with significant bearing on reindeer population dynamics. What are the causes and consequences of red noses in reindeer? Is it indicative of illness as Halvorsen suggests "The general consensus is that Rudolf has caught a cold". Perhaps it is a rare mutant phenotype that is destined to undergo a selective sweep thru reindeer populations via sexual selection (female reindeer find red noses sexy, right?) or via reducing reindeer mortality on foggy Christmas nights.

Nay, claims Halvorsen. "Rudolf is suffering from a parasitic infection of his respiratory system. To some this may seem a bit far-fetched as one would not expect an animal living with Santa Claus at the North Pole to be plagued by parasites, but I shall show otherwise."

Indeed Halvorsen goes on to show that reindeer, despite being residents of the North Pole (or at least the Svalbard archipelago at 80 degrees N) are liberally populated by parasites of all types, including at least 25 types of nematodes.

Notably these parasites have larval stages highly tolerant of freezing. They may have accompanied reindeer on their initial dispersal northwards, then adapted to the colder climes alongside of reindeer. In fact, Svalbard reindeer often have greater parasite loads than their mainland counterparts!

Halvorsen ends by writing, "So far we have not been able to quantify the combined effects of these parasites, but it is no wonder that poor Rudolph, burdened as he is by parasites, gets a red nose when he is forced to pull along an extra burden like Santa Claus."

Happy Holidays from the Evilutionary Biologist