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No. 131: SEP-OCT 2000

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Female Feral Fowl Foil Rapists

Male animals possess an inspired arsenal of devices to ensure that their sperm are the ones that fertilize chosen females. Their mechanical devices range from scrapers that physically remove sperm deposited by competing males to plugs that block sperm access in subsequent matings. It is claimed that some male ejaculates introduce not only fertilizing sperm but also "kamikaze" sperm specially designed to hunt down and destroy competing sperm.

Well, both sexes can play these games. Some females have ways to eject sperm from undesired males. For example, female feral fowl (hens gone wild!) prefer to mate with dominant males. Often, however, subdominant males force themselves on the females despite resistance and stress calls. The female response to such rapes is differential sperm ejection; that is, they immediately expel the unwanted ejaculate -- at least most of it -- raising the probability that they will be fertilized by the preferred dominant males.

(Pizzeria, T., and Birkhead, T.R.; "Female Feral Fowl Eject Sperm of Sub-dominant Males," Nature, 405:787, 2000.)

Comment. An interesting sort of sperm ejection occurs among Dunnocks, small brown birds common in English gardens. Alpha males try to prevent matings by lower-ranking males but are rarely successful. Most Dunnock matings are preceded by a ritual-like phenomenon called "cloaca-pecking." The female raises her tail exposing the cloaca. Instead of mating, the anticipating male pecks at the cloaca, an action that stimulates a pumping action and ejection of a droplet of sperm from previous matings. After the male inspects the droplet, normal mating follows. This bizarre scenario required the coordinated evolution of two different kinds of behavior (male and female) as well as the development of the female's sperm-ejection mechanism. See BBB23 in Biological Anomalies: Birds.

From Science Frontiers #131, SEP-OCT 2000. � 2000 William R. Corliss

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