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News: Giant sperm shows size matters for some animals.

Giant sperm shows size matters for some animals
Thu Jun 18, 2:03 pm ET
http://news.yahoo.com/s/nm/20090618/sc_nm/us_sperm_giant_1

LONDON (Reuters) – Tiny mussel-like creatures living 100 million years
ago made giant sperm longer than their own bodies, proving size has
always mattered for some animals when it comes to sex, scientists said
on Thursday.

Giant sperm are still around today. A human sperm, for example, would
have to be 40 meters long to measure up against a fruit fly's. The
insect is only a few millimeters in size but can produce 6 cm-long
(2.5 inch) coiled sperm.

Scientists have been unsure if such gigantism is a freakish one-off.

Now the discovery that ostracodes, an extinct ancient class of
arthropods, displayed the same trait shows that making giant sperm is
a long-standing and evolutionarily successful reproduction strategy.

"Giant sperm have been produced in at least some species over long
periods of time, even though they come at an extremely high price for
both males and females," said Renate Matzke-Karasz of the Ludwig
Maximilian University in Munich.

In most animals, including humans, reproductive success depends on
males producing a large number of tiny spermatozoa, while females
invest in a few large eggs.

But in some cases where sperm have to compete inside a female's body,
the chance of successful fertilization can be improved by increasing
the size of the sperm cell.

Matzke-Karasz and colleagues used a new imaging technique known as
"holotomography" to detect organs used for transferring giant sperm in
fossil remains of the ostracodes, which are only 1 mm long.

They described their findings in the journal Science.

--
Bob.

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