Anyone who has ever had to witness the horrific site of
mallard duck (Anas platyrhynchos) mating when taking
a young child for an innocent ‘feeding the ducks’ experience, will know the
discomfort it can produce. For those who do not, the defining reason for this
discomfort is the fact that mallard ducks often violently rape females during
mating. A little known fact is that females have developed their own anatomical
quirks, in what can be described as an evolutionary sexual arms race. As the
males have phalluses big enough not to require consent from females when
mating, female vaginas have spiral channels which twist in the opposite direction
to that of the male genitalia. In some cases, ducks have evolved cul-de-sac
pouches which prevent sperm from fertilising an egg, which allows the female to
have some control of the second half of the genetic material that will be
passed on to her offspring.
Recent research has discovered another traumatic mating
ritual in the animal kingdom. A species of sea slug (Siphopteron species 1) has been found to stab each partner
centrally in the forehead with an organ called a penile stylet, during
copulation. As the slugs are hermaphrodites (having both sets of reproductive
organs) there is a reproductive advantage to acting as the male when mating,
due to the potential to create more offspring by being free to fertilise other
slugs after copulation. By stabbing each other in the head and injecting a
secretion which has the ability to control the other slug’s behaviour and
prevent it from mating again, this may provide more time for the sperm to
fertilise the eggs and force the slug into the female role.
Another interesting mating technique is found in a certain
species of snake. Red-sided garter snakes (Thamnophis
sirtalis parietalis) mate in a mass orgy of slithering reptiles.
This is less traumatic for the animal but still pretty vile for the snake
fearing masses out there. The female produces a pheromone to attract male
snakes in great numbers, which creates a mating ball of competing males
surrounding the female. The pheromone can provide the following information to
the male: correct species, population, sex, season, reproductive condition and
age. The successful male who gets to mate with the female deposits a gelatinous
copulatory plug that can reduce the chances of the female re-mating and works
as a spermatophere (a protein matrix from which sperm are released as the plug
dissolves). This mechanism increases the chances of successful fertilisation
when competition is fierce and time is short.
Other research emphasises
the profound weirdness of mating in this species of snake. So called, ‘she-males,’
can also produce small amounts of this female sex hormone to trick male
red-sided garter snakes into courting them. As snakes are cold blooded, a
slower, weaker snake would have an advantage i
n creating warmth (needed in the
cooler spring months of the mating season) by attracting a mating ball to itself.
These examples of the
weird and wonderful ways in which animals create the next generation, only just
scratch the surface of the intriguing research being carried out on the topic.
It is a subject that both fascinates and disgusts in equal measure and will
continue to cause adults many awkward trips to the park with their own
offspring.
Further reading:
Brennan, P.L.R. et al. (2007). ‘Coevolution of male and
female genital morphology in waterfowl,’ PLOS
One, 2(5), pp. e418.
Frieson, C.R., Shine, R., Krohmer, R.W. and Mason, R.T.
(2013). ‘Not just a chastity belt: the functional significance of mating plugs
in garter snakes, revisited’, Biological
Journal of the Linnean Society, 109(4), pp. 893-907.
Lange, R., Werminghausen, J. and Anthes, N. (2014). ‘Cephalo-traumatic
secretion transfer in a hermaphrodite sea slug’, Proceedings of the Royal Society B, 281(1), pp. 1-6. (Published
online: 13 November 2013).
Parker, M.R. and Mason, R.T. (2012). ‘How to make a sexy
snake: estrogen activation of female sex pheromone in female red-sided garter
snakes’, The Journal of Experimental
Biology, 215(5), pp. 723-730.
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