Mesospermalege

The spermalege (also known as the organ of BerleseSiva-Jothy, M. T. (2006) "Trauma, disease and collateral damage: conflict in cimicids," ''Philosophical Transactions of the Royal Society B,'' 361, 269–275.) is a special-purpose organ found in female bed bugs that appears to have evolved to mitigate the effects of traumatic insemination. The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege.Reinhardt, K., Naylor, R. & Siva-Jothy, M. T. (2003) "Reducing a cost of traumatic insemination: female bedbugs evolve a unique organ," ''Proceedings of the Royal Society B,'' 270, 2371–2375. The evolution of the spermalege as a female counter-adaptation for traumatic insemination was first proposed by the French entomologist Jacques Carayon in 1966.Carayon, J. (1966) Traumatic insemination and the paragenital system. In ''Monograph of Cimicidae (Hemiptera—Heteroptera)'' (ed. R. L. Usinger), pp. 81–166. College Park, MD: Entomological Society of America.

Structure

The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege.

The ectospermalege is derived from the ectoderm. It consists of a groove in the right-handed posterior margin of the fifth sclerite, overlying a pleural membrane. In order to access the female's haemocoel during traumatic insemination, male bed bugs insert their needle-like penisRyne, C. (2009) "Homosexual interactions in bed bugs: alarm pheromones as male recognition signals," ''Animal Behaviour'', 78, 1471–1475. into the groove, and pierce the pleural membrane. This piercing produces wounds that leave melanised scars.

The mesospermalege is derived from the mesoderm. It is a membrane-bound sac attached to the wall of the haemocoel, directly beneath the groove of the ectospermalege. In all bed bug species except ''Primicimex cavernis,'' sperm are injected into the mesospermalege.Reinhardt, K. & Siva-Jothy, M. T. (2007) "Biology of the bed bugs (Cimicidae)," ''Annual Review of Entomology,'' 52, 351–374. The structure contains two main types of hemocyte, though their function is not yet fully understood. The first of these is phagocytic and may absorb seminal fluid, whereas the other may digest spermatozoa.

Function

The ectospermalege is visible externally in most bed bug species, giving the male a target through which to impale the female. In species without an externally visible ectospermalege, traumatic insemination takes place over a wide range of the body surface.

Exactly why males 'comply' with this aspect of female control over the site of mating is unclear, especially as male ''P. cavernis'' appear to be able to penetrate the abdomen at a number of points independent of the presence of an ectospermalege. One possibility is that mating outside the ectospermalege reduces female fecundity to such an extent that the mating male's paternity is significantly reduced ... The ectospermalege appears to act as a mating guide, directing the male's copulatory interest, and therefore damage, to a restricted area of the female's abdomen.

The spermalege structure serves to reduce the wounding and immunological costs of traumatic insemination. The piercing wound typically occurs in the exocuticle of the mesospermalege, and is repaired by "scarring substance" developed in the epidermis. At least nine species of bacteria and fungi have been identified from the male intromittent organ, and the mesospermalege reduces the likelihood of infection from such pathogenic organisms.

References

{{Reflist

Animal reproductive system
Cimicomorpha