This time, it's about chicken sperm. Specifically, whether roosters alter the quality of their sperm depending on how many other roosters they think have been, uh, laying with their hen—and what social status the hen, herself, has.
Believe it or not, studies in various species have shown that males in more dominant roles often produce a LOWER quality and quantity of sperm than those in subordinate roles. This is presumably because the dominant males don't have to compete as much as the subordinates, they get first pick of the females. But this hasn't been tested before, because the animals being studied understandably get annoyed when you try to get between them and their chosen female to get a sample of the semen.
In this case they decided to try again, using chickens. But not your normal chickens, these were Swedish fowl that live in social groups of up to 16 animals. The males form a dominance hierarchy for access to the females. The most dominant males are obviously going to get first crack at the hens, but the hens will often have multiple matings, and sperm competition is intense. Not only do the females go multiple times, the males can ejaculate up to 40 times within a few hours, which often results in quantity over quality, as the sperm quality decreases over time.
They took males of high and low status, and put them through randomized mating trials over several females, ALSO of high and low status. They took the ejaculate and measured the number of sperm, as well as the velocity, or how good their little swimmers were doing.
And the result? Well, you'll have to go read it. There are graphs that are integral to the story, and I don't want to spoil it. Suffice to say, chicken sperm is a lot more interesting than I would have previously guessed.
Image: Some rights reserved by quinn.anya
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