This is just a selection of the bizarre reproductive techniques that marine biologist Henk-Jan Hoving has discovered with different species of deep-ocean squid. He will be awarded a PhD by the University of Groningen (Netherlands) on 19 December 2008.
‘Reproducing in the deep ocean is a real challenge’, says Hoving. The deep ocean is unbelievably huge – 80 percent of the seafloor lies at depths of two kilometres or more. It’s not easy to find a partner in that gigantic, pitch-black environment. So, once you find one, you have to seize the moment. Squids that live in the deep ocean have developed a wide range of fascinating reproductive techniques to this end.
Hoving investigated the reproductive techniques of no fewer than ten different squids and related cuttlefish – from the twelve-metre long giant squid to a mini-squid of no more than twenty-five millimetres in length. Along the way he made a number of remarkable discoveries. Hoving: ‘Reproduction is no fun if you’re a squid. With one species, the Taningia danae, I discovered that the males give the females cuts of at least 5 centimetres deep in their necks with their beaks or hooks – they don’t have suction pads. They then insert their packets of sperm, also called spermatophores, into the cuts.’
Through the skin
With a different species, the Moroteuthis ingens, the spermatophores are introduced in a more peaceful way. ‘With this species the spermatophores penetrate the skin independently. They probably do that with the help of an enzyme-like substance that dissolves tissue.’ Hoving is the first to be able to prove that these sperm packets are able to penetrate the skin under their own steam. He discovered this when he experimentally placed spermatophores on the skin of just-caught individuals. His results are supported by an incident in Japan, where someone had to have an operation after eating squid to remove a spermatophore that lodged in his throat.
Sperm in reserve
When studying the mini-squid Heteroteuthis dispar, Hoving also made an extraordinary discovery. For the first time he found a squid that probably fertilizes its eggs internally. ‘The females have a pouch for storing sperm that is directly linked to the belly and the oviducts. This indicates that fertilization takes place within the body and not outside - which is more common for squid.’ Males fill the female’s pouch with a great deal of sperm. About three percent of the body weight of a female who has mated consists of stored sperm. This has a number of advantages. The females, who produce eggs over a long period, thus have a steady supply ‘in reserve’ which they can make use of. Another advantage is that when the pouch is full, no sperm from other males will fit.
Hoving was also the first to discover male squid with female characteristics. ‘Usually, squid have separate sexes. There are no hermaphrodites, as with snails. But with one species, Ancistrocheirus lesueurii, some of the males turned out to have small glands that in females are involved in egg production. They also had significantly longer bodies than “normal” males.’ Hoving cannot explain this phenomenon. ‘It’s possible that it’s the result of hormones and hormone-like substances that end up in the surface water as a result of human action – for example use of the pill – and then sink down to the deep ocean. However, it may also be an alternative reproductive strategy and a way of getting closer to the females.’
Hoving’s research has produced a wealth of information about deep-ocean squid. ‘Previously, there was little known about these organisms. That was because they were very difficult to study. The deep ocean is very inaccessible. Diving to such depths is only possible with the help of advanced technology.’ In order to gain an understanding of the reproductive habits of squid he had to use dead individuals, which he got hold of in many inventive ways. ‘For example, I’ve joined scientific expeditions but have also used examples that were found in the 1960s and 1970s in the stomachs of commercially caught sperm whales.’ Hoving hopes that his research will contribute to sustainable exploitation of the deep ocean. ‘Fishing is taking place at deeper and deeper depths. The deep ocean is a very vulnerable ecosystem, however. We desperately need to learn more about this ecosystem.’
Jos Speekman | alfa
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