AsianScientist (Oct. 29, 2018) – A research group in Japan has figured out the workings of the reproductive organs of an insect species with reversed genital structures. They published their findings in the journal eLife.
The Brazilian cave insect Neotrogla is of special evolutionary and morphological interest because of its reversed genital structures: the females of the species develop a penis. Neotrogla was first described in 2014 by an international group of scientists, including Associate Professor Kazunori Yoshizawa of Hokkaido University, Japan, and Associate Professor Yoshitaka Kamimura of Keio University, Japan. The discovery won them the Ig Nobel Prize in Biology in 2017.
In the present study, Yoshizawa and Kamimura focused on the unique, plate-like structure—not found in any other insect—at the entrance of the sperm-storage organ or spermatheca of Neotrogla females. During mating, the male injects liquid semen into the female’s spermatheca through the opening of the spermathecal duct at the tip of the female penis. The female can then use the content of the capsule not only for fertilization, but also for nutrients.
The researchers used optical microscopy, confocal laser scanning microscopy and high-resolution computed tomography to analyze the spermathecal plate located at the top of the female spermatheca. They also observed the flow of semen within the plate.
They discovered a tiny switching valve, 0.3 millimeters wide, at the entrance of the spermatheca, which can divert the flow of semen to channels on the left and right sides. The valve is made of a switch to direct semen flow, a fan-like muscle and a rubber-like protein called resilin that supports the muscle structure and protects the switch.
The switching valve structure of the spermathecal plate therefore allows Neotrogla females to receive two sperm capsules at once. The researchers speculate that such a valve allows the females to obtain greater amounts of semen, which leads to fierce competition over semen among females, thereby driving the evolution of the female penis.
Beyond the understanding of the insects’ sex lives, the researchers also suggested that a better understanding of the structure of the valve can help solve engineering challenges.
“This discovery could be applied in the design of nanotechnological devices,” said Yoshizawa.
The article can be found at: Yoshizawa et al. (2018) A Biological Switching Valve Evolved in the Female of a Sex-role Reversed Cave Insect to Receive Multiple Seminal Packages.
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Source: Hokkaido University; Photo: Kazunori Yoshizawa.
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