The motion of the ocean can carry you only so far. In the deep blue sea, female narwhals are on the prowl for males with the biggest tusks. Zackary Graham, a researcher at Arizona State University, and his colleagues recently published their research on tusk size as a factor in sexual selection:
Like walruses and elephants, male narwhals (Monodon monoceros) grow tusks; these are modified teeth. In narwhals, the left tooth erupts from their head, reaching more than 8 feet long in some individuals. The tusk grows out in a spiral pattern, giving the appearance of a sea-dwelling unicorn. [...]
When comparing individuals of the same age, sexually selected traits often exhibit disproportional growth — that is, for a given body size, sexually selected traits are often larger than expected in the largest individuals. Importantly, they compared the growth (or scaling) of the tusk to the scaling relationship between body size and a trait that is unlikely to have sexual functions. To do so, they used the tail of the narwhals, called the fluke.
"We also predicted that if the narwhal tusk is sexually selected, we expect greater variation in tusk length compared to the variation in fluke width," Graham said. This is because many sexual traits are highly sensitive to nutrient and body condition, such that only the biggest and strongest individuals can afford the energy to produce extremely large traits.
-via Dave Barry | Photo: Narly the Narwhal t-shirt now on sale at the Neatoshop