Wednesday, 1 July 2015

What Idiot Designed a Worm That Injects Sperm Into Its Own Head?

Macrostomum hystrix
Hypodermic self-insemination as a reproductive assurance strategy | Proceedings of the Royal Society of London B: Biological Sciences

You really have to laugh at creationism's 'Intelligent (sic) Designer' when you see the idiot stuff it supposedly designs.

Take this hermaphroditic flatworm that uses its penis as a hypodermic syringe to inject sperm into it's own head, for example! What sort of idiot would come up with a solution like that to the occasional problem of not finding another flatworm of the same species to exchange sperm with?

But it gets worse! The sperm then have to swim all the way down the length of the flatworm's body to get to the eggs in the tail, so they can fertilise them and produce what are, in effect clones of their parent.

Abstract

Self-fertilization occurs in a broad range of hermaphroditic plants and animals, and is often thought to evolve as a reproductive assurance strategy under ecological conditions that disfavour or prevent outcrossing. Nevertheless, selfing ability is far from ubiquitous among hermaphrodites, and may be constrained in taxa where the male and female gametes of the same individual cannot easily meet. Here, we report an extraordinary selfing mechanism in one such species, the free-living flatworm Macrostomum hystrix. To test the hypothesis that adaptations to hypodermic insemination of the mating partner under outcrossing also facilitate selfing, we experimentally manipulated the social environment of these transparent flatworms and then observed the spatial distribution of received sperm in vivo. We find that this distribution differs radically between conditions allowing or preventing outcrossing, implying that isolated individuals use their needle-like stylet (male copulatory organ) to inject own sperm into their anterior body region, including into their own head, from where they then apparently migrate to the site of (self-)fertilization. Conferring the ability to self could thus be an additional consequence of hypodermic insemination, a widespread fertilization mode that is especially prevalent among simultaneously hermaphroditic animals and probably evolves due to sexual conflict over the transfer and subsequent fate of sperm.

Hypodermic self-insemination as a reproductive assurance strategy
Steven A. Ramm, Aline Schlatter, Maude Poirier, Lukas Schärer
Proc. R. Soc. B 2015 282 20150660; DOI: 10.1098/rspb.2015.0660. Published 1 July 2015

This system is believed to have evolved out of hypodermic insemination commonly found in the platyhelminths where it evolved not to facilitate self-insemination but, "due to sexual conflict over the transfer and subsequent fate of sperm". So, evolution has exaptated a structure evolved for overcoming conflict so this flatworm can do something to itself that presumably it wants to do anyway.

There are very many examples of self-fertilisation to be found in the simpler multicellular organisms such as flatworms, roundworms, molluscs but none of them this bizarre. Most have a connection between the male and female germ cell producing organs which can be opened if necessary but the 'Intelligent (sic) Designer' apparently didn't think to use a system it had designed multiple times already, or design a similar simple method for this flatworm. Instead, it came up with a system of which William Heath-Robinson would have been proud, if only it had included some knotted string.

Believe it or not, there are still adults who find the idea of a magic invisible designer coming up with things like this to be far more convincing than a simple, evolutionary, unintelligent natural process. It's those creationists that deserver to be laughed at, not their imaginary invisible friend.

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