Surprise twist in a tail of seduction

25 April 1998

FEMALE swordtail fish go wild over males bearing brightly coloured,
streamer-like tailfins. But researchers now report that the conspicuous
coloration isn’t what attracts the female’s eye.

Given the choice, female swordtails spent more time looking at video clips of
an intact male swordtail’s sexual display than at the same clips after they had
been computer-altered to remove the tailfin. However, females divided their
attention about equally between images edited to show a tailless fish or a
fishless tail, indicating that the tail itself is not what turns the females on
(Proceedings of the National Academy of Sciences, vol 95, p 4431).

Instead, total size seems to be the key. When the researchers enlarged the
tailless image to be the same total length as the intact image, females showed
no preference between the two.