2.2 Violent mating: traumatic insemination in bed bugs and other

Author: Christine Sun

Introduction

In the animal kingdom, mating interactions are frequently marked by conflict (Johnston&Keller 2000). In sexually reproducing organisms, both the male and the female have conflicting strategies in optimizing reproductive fitness (Morrow et al. 2003). Although male fitness increases with the number of matings, female fitness is not increased and is often lowered. At the same time, however, the two sexes must meet somewhere in the middle to be able to successfully produce offspring. As a result, sexual conflict often leads to an evolutionary arms race between males and females (Rice&Holland 1997; Morrow et al. 2003; Lessells 2006). As Dawkins and Krebs phrased it, “as swords get sharper, so shields get thicker, so swords get sharper still”(Dawkins&Krebs 1979). One organism that displays sexual conflict is the common bed bug, Cimex lectularius .

The bed bug, which belongs to the Cimicidae family, has been known to parasitize humans for more than four million years (Reinhardt&Siva-Jothy 2007). While the organism itself is relatively common, the bed bug’s particular mating behavior is rarely found in other species. Although bed bugs have fully functional reproductive tracts, they reproduce solely by traumatic insemination (Usinger 1966 as cited by Reinhardt&Siva-Jothy 2007).

During traumatic insemination, the male pierces the female’s abdomen with his knifelike intromittent organ and injects his sperm through the wound into her hemocoel , the cavity that contains the hemolymph . The sperm travels throughout the female’s hemolymph and eventually reaches the ovaries, resulting in fertilization (Carayon 1966 as cited by Reinhardt&Siva-Jothy 2007).