Earwigs with two penises have a 'dominant penis' that is not the dominant hand, so why prefer to use either the left or right penis?
Earwigs are insects named because they have horny scissors that move at the tail end, but there is diversity in the 'number of penises', and among the species that leave a strong primitive characteristic, 'left and right' There is a group with 'one-to-two penises'.
Random or handedness? Use of laterally paired penises in Nala earwigs (Insecta: Dermaptera: Labiduridae) | Biological Journal of the Linnean Society | Oxford Academic
https://academic.oup.com/biolinnean/article-abstract/134/3/716/6357234
Half of These Earwigs Use Their Right Penis. The Other Half Use Their Left Penis. Why? | Science | Smithsonian Magazine
https://www.smithsonianmag.com/science-nature/half-of-these-earwigs-use-their-right-penis-the-other-half-use-their-left-penis-why-180978927/
Earwigs are insects whose most characteristic is the scissors that exist at the tail end, but some earwigs have not only the blade of the scissors but also two 'penises'. It can be said that it is characteristic to have only two penises, but there is a mysterious property that 'either the left or right penis is used preferentially' in a specific earwig.
Mr. Uemura, who had reported on the problem of the earwig's dominant penis, newly reported the latest findings on this problem.
Uemura et al.'S experiment started by capturing one male and six female Nala lividipes on Ishigaki Island, Japan, bringing them to the laboratory, breeding them in cat food, and breeding them. Uemura et al. Mated offspring born by breeding and found out by video recording 'Which penis the male uses, left or right'.
Male earwigs erect only one of the two penises toward the female during mating. When the penis used for mating was determined from this erect penis, 43.5% used the right penis for mating, 56.5% used the left penis, and most of the individuals except a few individuals used it. It was confirmed that 'the penis on the same side is used for the second mating'. It is said that 43.5% on the right side and 56.5% on the left side are statistically equivalent to about half, and when a similar experiment was conducted on Nala nepalensis, which is a similar species in Taiwan, 49.2% showed the penis on the right side. It was confirmed that 50.8% use the penis on the left side.
By the way, the earwig is an insect that looks like this. The left side is male and the right side is female.
Earwigs are mated by males and females facing each other and overlapping their bodies.
Furthermore, Mr. Uemura and his colleagues thought, 'Is there a case where only one penis is functioning?', And conducted an experiment in which one of the penises was removed after anesthetizing the earwig. Earwigs that have been given a period of time for recovery mated with females, so it does not mean that one penis is not functioning, but only one of the two penises that is functioning for some reason. It was confirmed that.
In previous studies, Uemura found that the majority (88.6%) of Labidura riparia preferentially use the right penis. It has a swirled fertilization sac, and its spiral swivel direction gives it an edge over the right penis. ' However, when Mr. Uemura visualized the structure of the genital organs using a fluorescence microscope, there were no anatomical signs that the female side had evolved to preferentially accept either the left or right penis, and the male. There were no signs of preferential development of either the left or right reproductive organs on the side.
An enlarged photo of the earwig's penis looks like this.
From this, Mr. Uemura considered, 'This result indicates that it is possible that which penis to use, left or right, is mainly determined by the neural control mechanism.' In other words, we decided that the property that earwigs have a dominant penis may be due to the 'brain' rather than the penis.
Uemura told Smithsonian magazine, who raised the question, 'It makes sense to have a backup penis if you damage your penis during mating, but why prefer one or the other?' 'Like other animals, learning improves performance has an impact,' he said. We believe that the repeated use of one side of the penis by the earwig will result in an improved efficiency of that side of the penis, resulting in a dominant penis. He said he plans to observe with (micro CT) to find the cause of his dominant penis.
Smithsonian magazine also reported an episode about Mr. Uemura's enthusiasm for earwigs, according to which Mr. Uemura was surprised at Mr. Uemura's existence once when he was surprised at the existence of Mr. Although he ran away, he was interested in the fact that he was protecting the eggs in the same position when he came to see the next day.
Uemura revealed that there is something interesting about earwigs in this study, but according to earwig expert Fabian Haas, research on earwigs was conducted on only a handful of 1942 species. Biologists who classify earwigs are 'less than a dozen.' 'It's difficult to get a lot of attention unless it's some important medical or agricultural discovery,' Smithsonian commented.
In addition, Mr. Uemura received the 2017 Ignobel Award for joint research with Associate Professor Kazunori Yoshizawa of Hokkaido University on 'an insect in which a female inserts a genital organ into a male instead of a male inserting the genital organ into a female'. But a known person. You can read an interview about winning the Ig Nobel Prize below.
Received the Ig Nobel Prize for research on 'male-female reversal insects' -new discoveries born from simple research-: [Keio University]
https://www.keio.ac.jp/ja/keio-times/features/2018/9/
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