Monday, January 29, 2007

Why Rodent Sperm Is Communist

University of Sheffield evolutionary biologist Simone Immler discover that, in certain species of rat and mouse, heads of sperm take on hook- or talon-like shapes. The larger the testes and more promiscuous the species, the more pronounced the claw-shape. The reasearch suggests that spiky-spermed males have the evolutionary advantage of spermatozoal cooperation:
Immler . . . and her collaborators reasoned there are times when sperm might want to cooperate. This might prove especially likely when animals are promiscuous and the sperm of one male have to compete against those of rival males.

. . . .

"Males in promiscuous species are better off by investing more into sperm production," Immler told LiveScience. "Hence, it has been shown that more promiscuous species have generally relatively larger testes."

. . . .

"When the finding of the European woodmouse was published a few years ago, it appeared to be an exceptional case occurring in this one species only," Immler said. "This research shows that when the pressure from rival males is high, individual sperm will cooperate with one another to ensure that at least one of their siblings successfully reaches the female egg."
Link. Don't these little gametes know that vigorous, free competition produces the optimal outcome? Leave it to a rodent to reject free-market capitalism. Damn hippies.

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Image credits: Sperm of a number of rodent species, Simone Immler, PLoS ONE, courtesy
LiveScience, borrowed for news-reporting and comment purposes.