The battle of the sexes in Coridromius

Before you read too far into this blog, I should first mention that this entry is going to talk about traumatic insemination. This complicated-sounding word is a form of reproduction for a few groups of animals, and if you'd prefer not to read or learn about sex in some unique bugs then this is a good point to stop reading.
   However, if you do choose to read on, there is a neat story that is being developed by a colleague of mine Dr. Nik Tatarnic about the secret sex lives of Coridromius, a genus of plant bugs that practices traumatic insemination.

Cute little Coridromius spp!

Traumatic insemination (TI) is a process where the male of an animal species injects sperm into the female outside of the "normal" structures associated with reproduction. Most animals have designated structures to send and receive sperm that co-evolve together. In the case of TI, the male "hijacks" the system by inserting his sperm in a location that hasn't co-evolved to receive it. This can cause many problems for the female: it causes physical damage because the males literally pierce their outer walls like hypodermic needles, and inject the sperm where it wasn't necessarily meant to go. This is why its considered traumatic. Females can get infections at the sites where the male injects his sperm, and the sperm can go to tissues that aren't meant to have it.

Bed bugs, another group that practices traumatic insemination. The male is injecting his sperm into the female where its not supposed to occur.

    One of the most common cited and studied cases of TI is with bed-bugs, or Cimicidae. The males have literally evolved hypodermic needle-like structures to inject the body cavities of females with sperm. The sperm then are absorbed into her body and then pass through her blood to fertilize her eggs. The females in the case of bed-bugs co-evolved with the males to re-route their reproductive system and accept the damage.
    However, Dr. Tatarnic has found a genus of bugs in the distantly related family Miridae that also practice TI. And what is odd about these bugs is that both the males and females have been rapidly evolving different structures to compete against each other, and the females "fight back"; a true war of the sexes. The first unusual thing he found about Coridromius is that even though most males had evolved a hypodermic-needle-like structures like the bed bugs to inject sperm into the females [upper right square in figure below], a few had also evolved unusual-shaped structures that take the form of a "screw" at the end [lower left square].

  The elaboration of the structures are thought to possibly help protect the females from the damage the males were making, and so there was evolutionary pressure to develop protective structures. These structures, or paragenitalia, were evolving at a rapid rate as well [right-hand images]. This is done by either blocking the area that males would go, or at least diverting the attack to an area that can control the damage, like a hardened pocket on the side of their bodies [dark tube-like areas on right-hand side].
  Dr. Tatarnic continues to work with these bugs, and has found many more species of Coridromius with even more unusual structures. However, why and how traumatic insemination involved in the first place for these bugs remains to be seen. May the battle continue!