The length of the tusks of the narwhal was influenced by sexual selection

The researchers compared the sizes of the tusks of the narwhal with a relative width of the tail and came to the conclusion that the length of the tusks of these animals is determined by sexual selection. Probably males narwhals show each other their superiority, crossing tusks, and use them in battle. It is unknown whether these bodies other functions. Article published in the journal Biology Letters.

Narwhals — marine mlekopitayuschie with huge tusks on the head that reaches three meters in length with a body size up to five meters. This is one of two teeth of animals, and so long he becomes only the males. Both females tooth and the second tooth of the males are hidden in the jaw and seldom developed. Scientists build a lot of conjecture about the function of the tusks of the narwhal, but none of them still has not been confirmed by convincing data.

According to one version, the animals use a huge tooth as an organ of chemical sense. And finds broken tusks, which are stuck into the body of another narwhal, and scars on the head indicate that animals can use the Tusk as a weapon. Also, the researchers watched as the males of the narwhal crossed their tusks, and we can assume that this body needs for inter – or vnutriposelkovyh interactions, for example, to attract females or fight for them.

However, the differences between males and females may lead not only to sexual selection, and, for example, environmental factors. To see how narwhals use their tusks in nature, and to study their function is hampered by the fact that these animals spend most of their life in Arctic ice, and researchers are difficult to get to them.

In such circumstances, to understand the functions of body parts you can use the tools of comparative morphology. Features that were the result of sexual selection, typically disproportionately large relative to body size of individuals. In the last century Robin best (Robin Best) conducted an analysis of the sizes of tusks relative to the body length in 35 narwhals of different ages and came to the conclusion that tusks evolved through sexual selection. However, the uneven growth of the parts of the body may be evidence not only of sexual selection, in addition to the result could be affected by the inclusion in the General analysis of immature and adult individuals.

To determine organ function, it is necessary to compare it with those parts of the body, the size of which is determined solely by the need for survival. Traits generates sexual selection usually vary more than other signs. Individuals who have few resources, are unable to allow yourself to spend money on attracting females, as well as those who are too invested in vital characteristics. And those individuals who have the size and degree of development necessary for optimal organs, can significantly improve attractive to females traits.

Scientists from the U.S., Greenland and Brazil under the leadership of Zachary Graham (Leroy Graham) from the University of Arizona studied the morphology of 245 adult narwhals for which data were collected from 1983 to 2018. The relative sizes of the Tusk compared with the relative width of the caudal fin. The size of the latter does not depend on sexual selection, and its variability can serve as a point of reference for comparison of the length of the tusks.

The ratio of the size of the Tusk to the length of the body best describes a parabolic curve, and the caudal fin is more appropriate linear model. This supports the hypothesis that the size of tusks is governed by sexual selection. Probably, the males use them to show other males their superiority. This explains the ritual crossing of the tusks: so animals can estimate the strength of each other, not wasting resources on the real fight.

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