Size really does matter in the mating game. So says a Syracuse University study in the November 8 issue of the journal Science.
Researchers studying sperm size in fruit flies found that females play an active role in determining the conditions under which sperm compete inside the female reproductive tract.
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The shape and physiology of the female reproductive tract drives wide variations in sperm size and shape.
Survival of the fittest Females in many species mate with more than one male during a single mating season and have specialised sperm-storage organs, says study co-author and biology professor Scott Pitnick.
The female collects the sperm from her various mates in this storage organ. The sperm from the different males then battle it out to see which gets to emerge and make that final dash for the egg.
Longer sperm wins out In this study, Pitnick and co-researcher Gary Miller used a species of fruit fly called Drosophila melanogaster to examine the connection between sperm size, female sperm-storage size and fertilisation.
They genetically manipulated the fruit flies and selected different groups based on sperm length and the length of the female sperm-storage organ.
They found that all males competed equally well when wooing females with short sperm-storage organs. However, male fruit flies with longer sperm put the boots to males with shorter sperm when courting females with longer storage organs.
The longer the length of the female storage organ, the more advantage for males with longer sperm.
Pitnick says these results show that the length of the sperm-storage organ is a mechanism that dictates female choice of which male becomes the lucky father. He compares long sperm tails to long peacock feathers.
A separate study found that the size of female sperm-storage organs drives the evolution of sperm length. – (HealthScout News)
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