In polyandrous species, even males who are mating successfully may have trouble siring offspring. For Mr. Right no. 2, it's a simple numbers game whether his sperm, the last guy's, or the next guy's will be the lucky choice of the female's ovum.

One oft-seen solution to this is territorialism: guard your mate jealously, and make it imprudent for her or her potential suitors to make a connection. But for many species, this method only goes so far: constantly fighting over one or more mates can have a huge energy cost, and may be unsuccessful -- especially since she may have a say in the matter.

Sperm competition changes the field of competition to the inside of the womb. Males attempt to produce more, better sperm than their peers, increasing the success of their matings rather than preventing their opponents'. Each extra sperm in their ejaculation is another ticket in the big raffle of Life.

One can clearly observe this strategy as an energy investment in the size of the testes. The classic example is a comparison between gorillas and chimpanzees. The social structure in which gorillas live supports the territorial strategy, allowing a successful male to maintain tiny testes (relative to his bodyweight). He's the only one playing the lottery! By contrast, chimpanzee males must have larger testicles to produce more sperm, since they live in more dynamic social groups that support multiple mates for each female. In fact, you can often infer things about current or past social structures in a species based on the size of the testicles.

Sperm competition usually refers to quantity of sperm, described above, but there are other interesting adaptations out there. Some species use hook sperm -- deliberately crippled sperm capable of waylaying other sperm -- to sabotage their competitors' exertions post-coitus. In fruit flies, the male employs a toxic sperm that may discourage the female from subsequent matings. And on a more positive note, mice sperm (from a single male) cooperate using formation flying to speed their approach to destiny.

Sources:
http://www.anthro.ucdavis.edu/features/stp/stpballs.htm
http://www.nature.com/nsu/020708/020708-10.html

Sperm Competition OR Everyone Really is a Winner

This race doesn't start at the sound of a gun, although projectile imagery is quite appropriate and welcome. It all comes down to this... there are no practice runs; well, there are, but either way, upwards of 200 million possible lives are extinguished each time duty calls, false alarm or not.

It all starts as a twinge fired from the sympathetic nervous system to the spinal nerves,which cause an intense spinal reflex via the pudendal nerve, known to the French as la petite mort, or “the little death”.


What does that mean for us down here in the gonads, you ask? It means all hell breaks loose, 'code red,' 'code red,'Elvis has left the building! I know you are new around here, you fresh little haploid you... don't look so god damn green! I'm telling you, when that alarm goes off, these walls around you – you do know that we are in the vas deferens right – they are going to squeeze together with a lot of force, and we are going to be squirted like toothpaste right outta the tube! Here is the secret... if you get a chance boy, swing by one of the seminal vesticles, and grab some of that seminal fluid... that stuff, that is our nitrous oxide boy, our NOS, it might just be the boost you need to acquire and make contact with the target.

Dang it boy, what do you mean, have you been through this before? Of course not! Weren't you listening?! This is a ONE shot deal... One shot! I hear that that is the price they pay for being able to pee standing up, but that is a whole new can o' worms. Yes I know I'm getting old, I've been in here for 3 days now... tell me about a lifetime boy, you would not believe the things I've seen. I am getting old, and although I might not make it, that is why I'm telling you all this, maybe you will make it. I'm not taking you under my flagella for nothing, hear?


You, dear reader, should feel quite good about yourself. After all, the mere fact that you are reading this suggests that you have overcome astronomical odds.

You triumphed in the race of all races. One to 200 million odds. When that call sounded, half of your potential chromosomes, in the form of a spermatozoa beat out the rest of all the sperm. You were that champion sperm. That is an incredible victory. If you can dominate in the race of all races, the race of potential existence, this life should be a cakewalk. When are you ever going to face adversity like that again?

Go on... pat yourself on the back,
after all,
you were conceived.

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