When does size matter?

Sexual competition forces drakes to grow longer penises

Evgenia Efimova, Vesti

Chemical signals emanating from people around us can have a profound effect on our physical condition. For example, many women have noticed "menstrual synchronicity" (still a mysterious phenomenon), thanks to which the fair sex, working or living in close proximity, have phases of this period at the same time.

Now, a study has shown that the social environment can also affect the size of the penis. At least among drakes. And although further research is needed to determine the specific factors affecting the size of the penis, the results published in the scientific publication The Auk: Ornithological Advances may help scientists in the future to develop treatments for erectile dysfunction.

The head of the study, Patricia Brennan from Mount Holyoke College, explained in an interview with Seeker that scientists often study drakes, among other things, because they are one of the few birds that have penises.

According to her, she wanted to check whether competition among males could affect the shape of their genitals.

"Drakes lived in beautiful open naturalistic buildings, and they quickly got used to the manipulations of scientists," she says. Brennan explained that by the word "manipulation" she means regular measurement of the penis of birds.

It turned out that feathered males react to sexual competition by growing a longer penis. An unusual phenomenon was observed in two studied species: The American sawfish (Oxyura jamaicensis) and the American sea blackfish (Aythya affinis).

Brennan and her research team compared the penises of birds that lived in pairs with a female with the penises of those individuals who lived in a group of other males (there were also females among them, but in smaller numbers). "If they were alone with the female, then the males just grew a normal–sized penis, and if they were among the males, they got the opportunity to change dramatically," says Brennan.

For the reason that evolutionary success depends on reproduction, the genitals are adapted to the various circumstances faced by the animal. Some male birds, for example, have corkscrew-shaped penises to move through the labyrinthine vagina of females. It is noteworthy that earlier studies by Brennan showed that such a feature in females developed in order to prevent access to unwanted males.

However, evolutionary changes in the size of body parts, as a rule, occur over entire generations, not one lifetime. Brennan wondered if the males of these birds could refute this theory. With the beginning of the mating season, the penises of drakes begin to increase in size, and at its end they decrease again. Similarly, for example, sea acorns (Semibalanus balanoides) – hermaphrodite sea creatures – grow their penises only at the moment when it's time to mate.

The study of birds lasted for two years. In the end, the scientists found that A.affinis grew longer penises when they were forced to compete for a female, compared to those who originally lived in pairs with her. A larger reproductive organ probably increased the chances of fertilization of the egg.

But the results obtained from observations of O.jamaicensis were more complex. During the first year, only the largest males in the groups grew long penises (about 18 centimeters). In the second year, the smaller males grew normal-sized genitals.

Birds have one of the largest penis–to-body ratios - scientists have even found a sexual organ that was longer than the creature's body. Birds are also known for the fact that they fight to the death. This suggests that the smaller O. jamaicensis may have been under stress to develop normal-sized organs. Bullying can increase the level of the stress hormone, and this interferes with the effect of androgen hormones that control the growth of the penis, the scientist explains.

Such a stress response can be adaptive. The same androgenic hormones that promote penis growth every season in birds may underlie the coloring of birds. The effect of such hormones leads to the fact that duck feathers change color from brown to chestnut during the breeding season. For females, the color of males signals the readiness of a man to continue the race, and for other males it portends a fight.

Portal "Eternal youth" http://vechnayamolodost.ru  21.09.2017