“Size isn’t everything!” That’s the statement that gets taught in almost every seminar that explains men how to talk to the female sex and/or how to go various steps further. But this statement can also be applied to a much more scientific fact. The size of the balls of mice definitely affect the number of sperms that this specific mouse can produce. A higher number of produced sperms increases the number of the male mouse to pass on his genes or how Stuart Wigby of the Oxford University says it: ”If you buy more tickets, you’re more likely to win.” More sperm helps those mice because usually there is more than one male mice trying to fertilise a female mouse. Of course, it is quite random whose sperm is reaching the female egg the first, but still the chance for mouse A is higher than the chance of mouse B to fertilise the egg if mouse A is able to ejaculate more sperm than mouse B. This is also called “sperm competition” and is also known in other animal species.
Now remains the question what makes this sperm competition so special? So far, it seems like a totally normal proof for Charles Darwin’s theory about “The Survival of the Fittest”, but it is much more than that. The size of the balls doesn’t correlate for hundred per cent with the produced amount of sperm. There are also rat that have offspring which produce more sperm than others although the balls of the ancestor weren’t significantly bigger. How is this possible?
In an experiment that the team of Stefan Lüpold from the Syracuse University in New York found out that birds that had this sperm competition also had more tissue that produced sperm. To challenge the theory about the correlation between the scientists from the University of Western Australia in Perth under the leadership of Renée Firman formed two groups of mice. One group lived in a monogamous system and didn’t have any sperm competition and the other group lived in a polygamous system with a lot of sperm competition. The mice in the monogamous system didn’t have any trouble with passing on their genes because there was no other male mouse that could compete with the one mouse. The completely opposite was the case with the polygamous system. There was a lot of sperm competition because every male mouse wanted to fertilise as many female mice as possible to guarantee that his genes will be passed on.
In an experiment that the team of Stefan Lüpold from the Syracuse University in New York found out that birds that had this sperm competition also had more tissue that produced sperm. To challenge the theory about the correlation between the scientists from the University of Western Australia in Perth under the leadership of Renée Firman formed two groups of mice. One group lived in a monogamous system and didn’t have any sperm competition and the other group lived in a polygamous system with a lot of sperm competition. The mice in the monogamous system didn’t have any trouble with passing on their genes because there was no other male mouse that could compete with the one mouse. The completely opposite was the case with the polygamous system. There was a lot of sperm competition because every male mouse wanted to fertilise as many female mice as possible to guarantee that his genes will be passed on.
The mouse that has the biggest testes has statistically the most offspring because it should fertilise the most female mice. In fact, after the 24th generation in the polygamous system the mice had bigger testes than the mice in the monogamous system. This example suggests that there must be a correlation in sperm competition and an increase of the size of the sperm producing tissue in mice. It is a good example for selective pressure. Firman himself says about the experiment that “Our mouse study is the first to provide unequivocal evidence that sperm competition selects for an increase in the density of sperm-producing tissue, and consequently, increased testes efficiency”.
The whole study seems to be a very clear indicator that mice can evolve due to sperm competition. There are still a few limitations of this experiment because in the nature there is usually not such a big competition as simulated in the study. That many mice don’t necessarily live all together at the same place which explains why the testes of mice are not constantly growing. Also can such big testes disturb during the hunt. This means that mice probably wouldn’t have to adapt that fast as they did in the case of the mice in the laboratory.
In conclusion I can say that of course this study proves not only the existence of an evolution of the testes of mice due to sperm competition, but it also is not completely realistic for the nature. I don’t think that mice can evolve that quickly in the nature because they usually don’t live that close together in the nature.
Source: https://www.newscientist.com/article/dn26845-mice-evolve-better-not-bigger-balls-in-sperm-race/
The whole study seems to be a very clear indicator that mice can evolve due to sperm competition. There are still a few limitations of this experiment because in the nature there is usually not such a big competition as simulated in the study. That many mice don’t necessarily live all together at the same place which explains why the testes of mice are not constantly growing. Also can such big testes disturb during the hunt. This means that mice probably wouldn’t have to adapt that fast as they did in the case of the mice in the laboratory.
In conclusion I can say that of course this study proves not only the existence of an evolution of the testes of mice due to sperm competition, but it also is not completely realistic for the nature. I don’t think that mice can evolve that quickly in the nature because they usually don’t live that close together in the nature.
Source: https://www.newscientist.com/article/dn26845-mice-evolve-better-not-bigger-balls-in-sperm-race/