Sexual Selection: Size DOES Matter for The Unicorns of the Sea

Researchers from Arizona State University have concluded that female narwhals actually choose males with the biggest tusk. In their research, Zachary Graham and his colleagues stated that:

« 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. »

[Source: Arizona State University | Via Neatorama | Picture Source: Narwhal Skewer T-Shirt]




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