Alternation of hemipenis use as a behavioural means of increasing sperm transfer in the lizard Anolis sagrei

Male lizards and snakes posses two functionally independent intromittent organs termed hemipenes, only one of which is intromitted into the female's cloaca during copulation. In the lizard Anolis sagrei, a significant proportion of males alternate in the use of the left and right hemipenes when the intercopulatory interval is 24 h or less but not when it is 72 h. This study investigated whether the observed alternating pattern of hemipenis use in A. sagrei is a behavioural means of increasing sperm transfer to females in successive copulations. Males that were experimentally prevented from alternating in the use of the hemipenes in two copulations separated by 1- or 24-h intercopulatory intervals transferred significantly fewer sperm in the second copulation than did males that were permitted to alternate. This difference was not observed when the intercopulatory interval was 72h. Males that were prevented from alternating in the use of the hemipenes in a series of three copulations, which were separated by 24 h, delivered significantly fewer sperm in the second and third copulations than did males that were permitted to alternate. These results support the hypothesis that alternation of hemipenis use is a behavioural means of increasing sperm transfer when the interval between copulations is relatively brief.