RAMOS, MM; IRSCHICK, D; CHRISTENSON, T; Tulane University, New Orleans,LA; Tulane University, New Orleans,LA; Tulane University, New Orleans,LA: The paradox of palp removal in the spider Tidarren sysiphoides: a performance advantadge?

Autotomy, the casting off of a body part, has evolved independently in several groups of organisms, and is thought to increase the short-term fitness of an individual in specific situations (i.e., escaping from predators or renewing damaged tissue). Nevertheless, such a loss can have profound negative effects on the animals� ability to move, digest food and reproduce raising the question as to why autotomy takes place. Male spiders of the genus Tidarren voluntarily remove a copulatory organ (one of two pedipalps) before attaining sexual maturity. We tested the hypothesis that palp removal in this genus enhances locomotor performance and hence might be important for fitness. We analyzed three different aspects of locomotion in the species Tidarren sysiphoides: undisturbed movement, maximum speed, and endurance. We examined both the undisturbed locomotion and maximum speed by filming the animals while moving on a single silk thread (5 cm) drawn across two small poles, while endurance was analyzed by pursuing the spiders until exhaustion. The spiders� undisturbed locomotion was generally highly intermittent, and the proportion of time spent pausing was significantly correlated with the average bout duration. While the spiders� undisturbed locomotion did not differ significantly after palp removal, maximum speed and endurance increased significantly. Because palp removal improved locomotor performance substantially, Tidarren spiders may have evolved autotomy to enable them to travel long distances in search of mates. (Supported by an NSF grant IBN 9983003 to D. Irschick)