Letters: Giant sperm

Published 30 January 1993


Your item on the advantages of large sperm (Science, 2 January) mentioned
only mammals. However, some invertebrate sperm make the bonobo’s look like
pygmies. Certain ostracods (small crustaceans), for instance, can have
sperm up to 15 millimetres long. This is all the more striking when you
consider that the males are only 2 millimetres long themselves. Monstrous
sperm can also be found in feather-winged beetles, backswimmers, fruit
flies and mites. The world record holder is a 20-millimetre sperm produced
by a fruit fly (Drosophila) species.

Interestingly, the groups in which giant sperm occur most commonly
(ostracods and feather-winged beetles) are also very promiscuous. Perhaps,
therefore, these giant sperm are used to block the passage of competing
sperm to the unfertilised ova. Further evidence to support this interpretation
comes from the shape of the sperm, which have a swollen posterior that neatly
plugs the female tract. Large sperm may be good competitors, but it seems
that giant sperm can be even better.

Richard Ladle, Rufus Johnston Department of Zoology University of Oxford