Spermalege
Encyclopedia
The spermalege is a special-purpose organ found in 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. The evolution of the spermalege as a female counter-adaptation for traumatic insemination was first proposed by Jacques Carayon
in 1966.
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 penis
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. 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.
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.
Traumatic insemination
Traumatic insemination, also known as hypodermic insemination, is the mating practice in some species of invertebrates in which the male pierces the female's abdomen with his penis and injects his sperm through the wound into her abdominal cavity . The sperm diffuse through the female's hemolymph,...
. The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege. The evolution of the spermalege as a female counter-adaptation for traumatic insemination was first proposed by Jacques Carayon
Jacques Carayon
Jacque Carayon was a French entomologist, best known for his pioneering research into traumatic insemination. Carayon was Chairman of Entomology at the National Museum in Paris from 1975-1985.-Career:...
in 1966.
Structure
The spermalege has two embryologically distinct parts, known as the ectospermalege and mesospermalege.The ectospermalege is derived from the ectoderm
Ectoderm
The "ectoderm" is one of the three primary germ cell layers in the very early embryo. The other two layers are the mesoderm and endoderm , with the ectoderm as the most exterior layer...
. It consists of a groove in the right-handed posterior margin of the fifth sclerite
Sclerite
A sclerite is a hardened body part. The term is used in various branches of biology for various structures including hardened portions of sponges, but it is most commonly used for the hardened portions of arthropod exoskeletons....
, overlying a pleural membrane. In order to access the female's haemocoel during traumatic insemination, male bed bugs insert their needle-like penis
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
into the groove, and pierce the pleural membrane. This piercing produces wounds that leave melanised scars.
The mesospermalege is derived from the mesoderm
Mesoderm
In all bilaterian animals, the mesoderm is one of the three primary germ cell layers in the very early embryo. The other two layers are the ectoderm and endoderm , with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme , mesothelium, non-epithelial blood corpuscles and...
. 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. The structure contains two main types of hemocyte
Hemocyte
A hemocyte is a cell that plays a role in the immune system of invertebrates. It is found within the hemolymph.Hemocytes are phagocytes of invertebrates....
, 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 fecundityFecundityFecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
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
Epidermis (zoology)
The Epidermis is an epithelium that covers the body of an eumetazoan . Eumetazoa have a cavity lined with a similar epithelium, the gastrodermis, which forms a boundary with the epidermis at the mouth.Sponges have no epithelium, and therefore no epidermis or gastrodermis...
. At least nine species of bacteria and fungi have been identified from the male intromittent organ
Intromittent organ
An intromittent organ is a general term for an external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most aquatic species fertilize their eggs externally, although there are...
, and the mesospermalege reduces the likelihood of infection from such pathogenic organisms.