Men, can live with them, can live without them

Sex is not necessary for all members of the animal kingdom. Of course it has its advantages, primarily, combining genetic material adds to the diversity of a species and makes it more ‘hardy’. But in vertebrates, organisms that are considered ‘more complex’ (ie. fish, amphibians, reptiles, birds and mammals) asexual reproductions is extremely rare and is thought to be limited because of the complexity of vertebrate genetics and body plans.

Recent discoveries has defied this logic however. A captive female hammerhead shark had a ‘virgin’ birth. The shark, which lives at Henry Doorly Zoo in Nebraska gave birth to a pup despite having had no contact with a male. A similar incidence was reported of a komodo dragon in Chester Zoo in the UK.

Originally it was thought that the females were storing sperm from a previous encounter for an extended length of time but genetic tests have now confirmed that the offspring share their DNA with only individual, their mother. This type of reproduction is known as parthenogenesis and it not entirely clear how or why it developed. One theory suggests that it evolved as a mechanism to deal with times of isolation. For example, if a komodo dragon found itself on an island without a mate, a few offspring could be produced while it waited for another komodo dragon to arrive and the population could be sustained until a viable breeding pool arrived.

This new ‘twist’ has created many questions including what other animals are capable of reproducing in this fashion. So far the ability has not been documented in mammals and birds but it has only been with the recent advent of genetic testing that such unusual cases can be investigated.

Cooperative Mating Behaviour in Sharks

Looking through some of Brian Larnder’s past post of Sexiest Animal on the Planet, I discovered this interesting article on sharks. I was surprised to learn about the advantages of male sharks engaging in teamwork to inseminate a female!

Terrifying Turtle Organs

Check out Darren Naish’s posting on Terrifying Sex Organs of Male Turtles. I believe this post coins a new phrase, “Hung like a turtle”.

Sexy Sponges

Check out this week’s Sexiest Animal on the Planet: Sponges over at the Primodial Blog. As Brian Larnder says, you’ll never look at a sponge the same way again.

Bedbugs Shoot Up Too

In follow up to Monday's post on Giant Squids Shooting Up, the behaviour of ‘injecting’ sperm directly into the female is not limited to the giants of the seas. A male bedbug of the genus Cimex uses a spike on his penis to pierce a hole through the female's back. He then ejaculates into this hole and his sperm swim around the female's blood until they reach her ovaries. The fertilized eggs then develop into embryos which are born alive in the usual manner. How and why such a system developed is a mystery.

Giant Squids Shoot Up

Living in harsh environments such as hot deserts, deep seas and high mountains means that potential mates are few and far between so when you encounter another member of your species, you have to grab the opportunity. The Giant Squid (Architeuthis) is one such animal. It lives in dark deep depths 1000m below the ocean surface. These tentacled creatures meet rarely and are even more rarely observed by humans.

These giants beasts can reach lengths of 15m (45ft) and the male delivers his load by means of a 1m (3ft) long muscular, prehensile penis. But instead of making the delivery in a conventional fashion, he actually stabs the female with his appendage and deposits sperm into the wound. A female giant squid captured off of Australia’s southern coast had sperm embedded in her arms.

This allows the female to store the sperm for long periods, a useful option since encounters with males are infrequent at these great depths. It is not clear how the female uses the sperm when she is ready to fertilize her eggs. Perhaps she reopens the wound to retrieve the souvenir he left behind or maybe hormonal cues cause sperm migrates to the surface.

A male giant squid caught off Norway in the 1950s also had sperm embedded in his skin. This seems odd but when you are a lonely animal living in a vast, empty world you have take action when a the opportunity presents itself. Shoot first, ask questions later.