10 interesting facts about animals mating

This post is a result of a conversation Yumchia, the Pretty Lady and I had over lunch at Gidleigh Park. We continued the discussion on the drive back to London, and Yumchia asked me to do a post on the subject of chickens and eggs. So I tried, but I couldn't find enough stuff to make a full post, so I thought I'd do a list post. It's more interesting and has far more detail, although in this case it may be excessive. Here goes.

1. Chickens and eggs.

Most of the eggs available in supermarkets are unfertilised ova. That is, the cockerel has not fertilised the egg by mating with a hen. Cockerels have no penis - instead the hen inverts her cloaca to receive sperm from the cockerel's cloaca. Video embedded below (it's about 1 minute in).



2. Duck penises and wrong turns.

Female ducks are devious. Their cloacas (the avian and reptilian version of a vagina) curve, twist, branch and have dead ends. This is thought to enable the female duck to select sperm from the male she likes best to fertilise her eggs. The male duck has also evolved some impressive equipment in order to get around the female's defences. See here, for some impressive images.

3. Gorillas, harems, and effort.

Among primates, gorillas have the smallest testes and penis relative to the size of their body. Gorillas' penises measure a length of just 2 inches on average, compared to a human's 5-7 inches on average. The reason is thought to be because gorillas live in harem-like family groups, where a single male silverback has sole access to several females (adjacent image is from the Dian Fossey Gorilla Fund site). He can therefore be certain that any sperm that fertilise the females in his harem are his, and so he can get away with producing less sperm than, say, a chimpanzee. The chimp needs to produce more sperm and has bigger testes to do so, since his sperm needs to contest with other chimps' sperm. In case you were wondering, humans have medium size testes (because humans are mostly monogamous) and big penises (because size really does matter and female primates pick males with bigger penises).

4. Boars and the perils of experimentation.

Pigs' penises curve, ending in a spiral, and are between 45 and 60cm long. The boar's penis engages with the sow's cervix (not vagina), which is also spiral shaped. So the boar needs to be fairly adept and manipulating it in order to fertilise the sow. More details here. And for an eye-watering story, see here.

5. Humans and axolotls - reproducing without growing up.

Axolotls are interesting creatures. They are thought to be a type of salamander, and indeed are very similar to the larval stage of some species of salamanders. However, they become sexually mature, mate and reproduce while still in this larval stage (the technical term for it is "neotenous"). It's possible to turn an axolotl into a salamander with hormone injections. All well and good - except that the same is hypothesised to apply to humans too! Humans are similar to chimpanzee babies. They share hairless, flat faced, small teeth, thin skull bones and a number of other characteristics. It's possible that humans are apes that never grew up. More here.

6. Anglerfish and their deep attachment to each other.

Anglerfish are a deep sea fish with lures hanging off their foreheads, often with a bioluminescent tip, which they use to lure unsuspecting prey into their jaws. The fish of the family Ceratiidae are solitary, and males and females rarely meet. To perpetuate their species, the male, which is much smaller than the female, fuses himself to the female, becoming nothing more than a pair of sperm producing organs. More here, and the adjacent image is from Te Ara. This leads nicely to...

7. Polychaete worms and sexual dimorphism.

...polychaete worms of the genus Osedax, which live on whale falls (occurring whenever the corpse of a whale falls to the ocean floor). Males live inside the female, never developing past the larval stage, producing lots and lots of sperm. This looks quite close to asexual reproduction, with the only gene shuffling occurring during meiosis.

8. Dolphins, whales, and keeping it hidden.

Dolphins and whales need to swim to find food, and by and large, they need to swim fast. External genitalia, therefore, are a hindrance, creating drag and reducing top speed. So male dolphins and whales have evolved a way to keep their genitalia in a pouch, extruding them only when mating. It's actually quite impressive.



9. The Iberian minnow and complete, total male lib.

There's a species of freshwater fish, Squalius alburnoides, that consists entirely of males. Species that consist of females are known, and even hammerhead sharks can reproduce by parthenogenesis. However, this species of fish reproduces by mating with females of another species. They produce female and female hybrids (triploid) and male pure breds (diploid). So these minnows don't need females. Emile of The World We Don't Live In explains it better than I ever could here.

10. Snakes - how?

Apparently it's quite complicated. Video here. The male snake needs to join his cloaca to the female snake. He has two penises, and only needs to insert one into her cloaca. Flexible spines on it then expand, preventing it from getting dislodged. He can then deposit his sperm. The female sometimes pulls the male along during mating, and he will try to mate with her again after a few hours. Another video below:




So there you have it. This blog is no longer family friendly, and should only be viewed after the watershed, when any young children should be fast asleep in bed.