October 17, 2018
Hokkaido University
Keio University
Highlights of this research
Discovery that the females of the sex-reversed cave insect *Neotrogla* possess a valve to switch the flow of semen.
While organisms have evolved various types of valves, such as check valves in the heart to prevent backflow, this is the first time a switching valve has been identified.
It is hypothesized that the ability to retain more semen (nutrients) using this switching valve is one of the factors that drove the evolution of the female penis.
An international research group, including Associate Professor Kazunori Yoshizawa of the Research Faculty of Agriculture at Hokkaido University and Associate Professor Yoshitaka Kamimura of the Department of Biology at Keio University, has discovered the existence of a switching valve in *Neotrogla*, an insect in which females have a penis. This is the first time such a valve has been found in any organism.
During mating, the male *Neotrogla* transfers a capsule containing sperm and nutrients to the female. The increased proceptivity of females for mating, driven by competition for these nutrients, is considered the primary factor behind the evolution of the female penis. The newly discovered switching valve is located at the entrance of the female's sperm storage organ. This allows the female *Neotrogla* to receive twice the number of seminal capsules at once compared to insects without such a valve. It is thought that as a result of being able to receive more semen, the competition among females for the nutrients it contains intensified, which in turn promoted the evolution of the female penis.
The findings of this study were published in the journal *eLife* on October 16, 2018.
Please see below for the full press release.