Tuesday, 27 Jan, 2009 Health & Fitness

Spermatozoa's Quality Plays An Important Role In Evolution


Though the question about the influence of spermatozoa's sizes and speed on one's individual success is still to be discussed, according to John Fitzpatrick and his colleagues from the University of Western Australia and McMaster University from Canada, these criteria certainly have an influence on the creation of new species and even on the natural selection.

Scientists had kept up to this theory for a long time, but more detailed research showed that it isn't a very reliable one.

In order to increase a spermatozoon's speed, scientists need to lengthen its tail and energy reserves. However, this leads to the increase of its size and, as a consequence, to its liquid resistance. A number of mathematical and practical studies on mammals' spermatozoa showed that a big size and length do not result in maximum speed at all.

The second theory, submitted to critics lately is linked to the relation between speed and success. As biologists proved, "the fastest" doesn't always mean "the most efficient". The mechanisms of the selection after the end of a sexual act can work as well, being characteristic for the sexual organs of female mammals. These mechanisms allow the females to stop the spermatozoa they didn't like.

Thus, the theories viewing spermatozoa's evolution are always changing, because of this multitude of factors.

Some scientists consider that the main factor is the speed, others consider it's the size of the spermatozoa. The last ones are also divided into 2 groups: some of the arguments are for big gametes, and others – for small ones. The arguments for small gametes are motivated by the ability of some small gametes to remain invisible for the protective systems of the female sexual organs.

This is partially the reason why Fitzpatrick chose for his experiment a certain species of fish from the family of cichlids. These species live in the African lake Tanganyika. Thanks to their external reproductive system the maternal role in sperm selection is minimal. The authors of the publication in the Proceedings of The National Academy of Sciences also showed interest in intensive new species creation. Besides, their spawn may be fertilized by some males in the same time.

Scientists decided to carry out a "contest" for the spermatozoa of 29 genetically similar types of these species of fish, all of them living in the same lake. It wasn't hard for them to establish the motivation of the natural selection.

As they predicted, the natural selection was made on the basis of 4 factors: length, size, vitality and quantity of spermatozoa in the ejaculation.

This doesn't mean that only the parameters of gametes play a role in natural selection. The ability of finding food and hiding from animals that might eat them is also very important – only such species can reach a sexually mature age. Thus, even the fastest spermatozoa will give start to a new organism, but they won't be able to continue their generation.

Posted by summer_rain

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