Posted: Jun 30, 2011 5:00 am
Most here will be familiar with the basics of mating amongst sexually differentiated organisms. Leaving aside for a moment yeasts, which have a peculiar sexual differentiation that is considered to be an earlier, antecedent form prior to the emergence of male and female, and concentrating upon those organisms that possess a recognisable male and female sex, most mating transactions between these organisms follow a basic pattern, in which males seek to transfer their sperm to females via some means. Probably the simplest system is seen in mosses, in which the male organisms simply release their sperm into the moisture covering their surfaces, and the sperm swim through that moisture to an adjacent female moss. However, once we move into the world of metazoans, life starts to become more complicated.
For one thing, female investment in reproduction is usually greater than that of the male. Consequently, it pays for a female to be discriminating with respect to mating partners, and reserve her unfertilised eggs for the choicest suitor. Males, on the other hand, have a vested interest in finding ways around that. Whilst tracking down some literature on insect phylogeny, I alighted upon some truly bizarre variations on the mating theme, which I think everyone will appreciate me sharing here, and which, whilst being bizarre to our way of thinking, are still eminently within the remit of evolutionary theory to explain, and indeed, only make sense within an evolutionary paradigm.
The first example I'll give is the spider species Harpactea sadistica, whose taxonomic name derives directly from its interesting mating habits. Males of this species bypass the usual mating process, and, upon having subdued a female, instead of using the pedipalps to deposit sperm in the female's spermatheca (the usual procedure in spiders), chooses a more direct mating route. Using modifications of the pedipalps resembling hypodermic needles, he injects his sperm through the female's body cavity, aiming precisely for her ovaries. It should not require much imagining why the specific name sadistica was chosen for this unique spider.
However, there are other examples of what might be termed 'hypodermic insemination'. Many of the unusual species belonging to the Order Strepsiptera, a group of parasitic insects that are themselves a taxonomic headache of 200 years duration, courtesy of their quixotic morphology, again bypass the usual business of joining genitaila in order to mate. In this case, because the females have no genitalia to speak of. The usual collection of chitinous parts seen in other female insects is either vestigial or absent, and the male mates with the female by inserting his hypodermic copulatory organ behind the female's head. Here is located a brood canal, which the male has to rupture in order to gain access. Even more weirdly, the female Strepsipteran hatches the eggs inside her own body cavity, and the first instar larvae swim around in her haemolymph until it is time to emerge into the outside world, which they do through the same brood cavity that the male subjected to attack earlier. Indeed, female Strepsipterans have largely given up on possessing virtually all of the usual adult insect features, lacking eyes, limbs, genitalia and being little more than a sort of bag with a mouth at one end. The males, possessing a full set of eyes, limbs and wings, have to move pretty sharply in order to copulate with these seemingly unprepossessing partners, because an adult male Strepsipteran has no mouthparts, and his energy reserves run out after about five hours, whereupon he comes crashing to a halt and dies.
Slightly less weird from the point of view of morphology, but again, weird from the standpoint of dispensing with the usual sexual etiquette, is the familiar Bed Bug. Males once more simply stick their copulatory organs through the female's body wall. However, just to add a little spice to the proceedings, the species has evolved an interesting development in the female - a set of paragenital organs that act as a sort of 'bulls eye' marker for the male. Quite a few Hemiptera have developed this arrangement, but the Bed Bug is the species that is best studied.
One Hempiteran species that is gaining increasing attention from scientists, is a flower bug called Xylochloris maculipennis. Like the familiar Bed Bug, this species discards the usual sexual etiquette, and the male simply drives his penis through the female's body wall. But in another bizarre twist, males of this species will also perform the same act upon other males. It is hypothesised that this instance of homosexual hypodermic insemination is a means of decommissioning the genitalia of rival males, though research has yet to answer conclusively this and several other questions about the wacky sex life of this bug species. However, the injected sperm appear to head straight for the testes of the recipient, where they are digested, giving the recipient a protein and energy boost at the expense of the male that performed the injection. It is therefore possible that some males may give off female signals to a rival male, in order to waste that male's sexual investment, and remove him from competition.
However, perhaps the oddest of all these organisms is a Rotiferan, known as Asplanchna brightwelli. In order to inseminate the female of the species, the male dissolves a hole in her side.
And as if all of this were not strange enough, it's possible that some species use this abandonment of sexual etiquette as an ecological weapon. Hesperocimex sonorensis and Hesperocimex cochimiensis are two bug species that share an ecosystem (they are blood sucking parasites upon the same bird species), and which both practice hypodermic insemination. However, it's possible that the latter species uses sex as a weapon to displace the former. If a male H. cochimiensis inseminates a female H. sonorensis, the result is a massive, rapid and lethal immune reaction. Which means that cochimiensis may use cross-species sex in order to remove food rivals from the scene, by using shagging as a biological weapon.
Just when you thought biology couldn't come up with anything more that boggled the mind, along comes yet another collection of organisms that make you think "WTF?". In this, case, literally.
For one thing, female investment in reproduction is usually greater than that of the male. Consequently, it pays for a female to be discriminating with respect to mating partners, and reserve her unfertilised eggs for the choicest suitor. Males, on the other hand, have a vested interest in finding ways around that. Whilst tracking down some literature on insect phylogeny, I alighted upon some truly bizarre variations on the mating theme, which I think everyone will appreciate me sharing here, and which, whilst being bizarre to our way of thinking, are still eminently within the remit of evolutionary theory to explain, and indeed, only make sense within an evolutionary paradigm.
The first example I'll give is the spider species Harpactea sadistica, whose taxonomic name derives directly from its interesting mating habits. Males of this species bypass the usual mating process, and, upon having subdued a female, instead of using the pedipalps to deposit sperm in the female's spermatheca (the usual procedure in spiders), chooses a more direct mating route. Using modifications of the pedipalps resembling hypodermic needles, he injects his sperm through the female's body cavity, aiming precisely for her ovaries. It should not require much imagining why the specific name sadistica was chosen for this unique spider.
However, there are other examples of what might be termed 'hypodermic insemination'. Many of the unusual species belonging to the Order Strepsiptera, a group of parasitic insects that are themselves a taxonomic headache of 200 years duration, courtesy of their quixotic morphology, again bypass the usual business of joining genitaila in order to mate. In this case, because the females have no genitalia to speak of. The usual collection of chitinous parts seen in other female insects is either vestigial or absent, and the male mates with the female by inserting his hypodermic copulatory organ behind the female's head. Here is located a brood canal, which the male has to rupture in order to gain access. Even more weirdly, the female Strepsipteran hatches the eggs inside her own body cavity, and the first instar larvae swim around in her haemolymph until it is time to emerge into the outside world, which they do through the same brood cavity that the male subjected to attack earlier. Indeed, female Strepsipterans have largely given up on possessing virtually all of the usual adult insect features, lacking eyes, limbs, genitalia and being little more than a sort of bag with a mouth at one end. The males, possessing a full set of eyes, limbs and wings, have to move pretty sharply in order to copulate with these seemingly unprepossessing partners, because an adult male Strepsipteran has no mouthparts, and his energy reserves run out after about five hours, whereupon he comes crashing to a halt and dies.
Slightly less weird from the point of view of morphology, but again, weird from the standpoint of dispensing with the usual sexual etiquette, is the familiar Bed Bug. Males once more simply stick their copulatory organs through the female's body wall. However, just to add a little spice to the proceedings, the species has evolved an interesting development in the female - a set of paragenital organs that act as a sort of 'bulls eye' marker for the male. Quite a few Hemiptera have developed this arrangement, but the Bed Bug is the species that is best studied.
One Hempiteran species that is gaining increasing attention from scientists, is a flower bug called Xylochloris maculipennis. Like the familiar Bed Bug, this species discards the usual sexual etiquette, and the male simply drives his penis through the female's body wall. But in another bizarre twist, males of this species will also perform the same act upon other males. It is hypothesised that this instance of homosexual hypodermic insemination is a means of decommissioning the genitalia of rival males, though research has yet to answer conclusively this and several other questions about the wacky sex life of this bug species. However, the injected sperm appear to head straight for the testes of the recipient, where they are digested, giving the recipient a protein and energy boost at the expense of the male that performed the injection. It is therefore possible that some males may give off female signals to a rival male, in order to waste that male's sexual investment, and remove him from competition.
However, perhaps the oddest of all these organisms is a Rotiferan, known as Asplanchna brightwelli. In order to inseminate the female of the species, the male dissolves a hole in her side.
And as if all of this were not strange enough, it's possible that some species use this abandonment of sexual etiquette as an ecological weapon. Hesperocimex sonorensis and Hesperocimex cochimiensis are two bug species that share an ecosystem (they are blood sucking parasites upon the same bird species), and which both practice hypodermic insemination. However, it's possible that the latter species uses sex as a weapon to displace the former. If a male H. cochimiensis inseminates a female H. sonorensis, the result is a massive, rapid and lethal immune reaction. Which means that cochimiensis may use cross-species sex in order to remove food rivals from the scene, by using shagging as a biological weapon.
Just when you thought biology couldn't come up with anything more that boggled the mind, along comes yet another collection of organisms that make you think "WTF?". In this, case, literally.