Meeting Abstract

39.1  Monday, Jan. 5  Gravidity degrades escape performance in threespine stickleback MCGEE, M.D.; Univ. of California, Davis mcgee@ucdavis.edu

Traits that increase reproductive success while increasing predation risk have been well documented in males, but a similar phenomenon may also exist in females. Just as males with sexually selected ornaments may experience an increased predation rate, females may experience increased predation because gravidity impedes escape performance. To test this, I used wild-caught marine threespine stickleback, Gasterosteus aculeatus. I divided the fish into two groups, 12 gravid females and 7 nonsexual individuals, which were defined as fish with no obvious gravidity or male nuptial coloration. I filmed fast-starts for both groups at 250 frames per second using a mirror placed at a 45 degree angle below the tank to generate a ventral image. I triggered fast-start responses by rapidly bringing a dipnet handle down near the vicinity of the fish. I filmed at least 5 escape responses per fish, and used the trial with the best overall escape performance for statistical analysis. Both groups were then massed, subjected to an egg removal procedure, and massed again. Each individual was allowed to recover for at least 24 hours, then filmed for fast-starts again. Measures of fast-start performance included net distance traveled, maximum velocity, maximum acceleration, and the bending coefficient. Gravid female stickleback exhibited poorer overall escape performance than both nongravid stickleback and gravid females after eggs had been manually removed. Other studies on fast-starts suggest that a decrease in escape performance of this magnitude is likely to strongly affect the ability of a gravid female stickleback to avoid capture during a predation event. These results, combined with observed variation in clutch mass between females, suggest a potential tradeoff between high fecundity and the ability to effectively evade predators.