The longer the better: evidence that narwhal tusks are sexually selected

Once thought to be the magical horn of a unicorn, narwhal tusks are one of the most charismatic structures in biology. However, narwhals spend most of their lives hidden underneath the Arctic ice, which makes testing the function of the tusks nearly impossible. Over the course of 35 years, we collected morphology data on 245 adult male narwhals to shed light on the function and selection pressures that have acted on this exaggerated trait. Based on the disproportional growth and immense variation in tusk length that we found, we demonstrate that narwhal tusks are indeed sexually selected, and believe that they likely function as signals during male-male aggression or mate choice.

一角鲸（narwhal）的长牙曾被误认为是独角兽的魔法角，是生物学领域最具魅力的结构之一。然而，一角鲸的一生大多隐匿于北极冰层之下，这使得对其长牙功能的研究几乎难以开展。本研究团队历时35年，收集了245头成年雄性一角鲸的形态学数据，以期阐明该夸张性结构的功能以及作用于其上的选择压力。基于观测到的异速生长现象与长牙长度的巨大个体差异，本研究证实一角鲸的长牙确实是性选择的产物，并认为其极有可能在雄性间争斗或配偶选择中充当信号。