33.3 Thursday, Jan. 5 Environmentally Correlated Divergence in Morphology and Climbing Performance in Waterfall-climbing Fish from Hawai’i and Kaua’i BLOB, R.W.**; KAWANO, S.M.; MOODY, K.N.; BURCHFIELD, H.J.; MAIE, T.; PTACEK, M.P.; SCHOENFUSS, H.L.; Clemson Univ.; Clemson Univ.; Clemson Univ.; Clemson Univ.; Clemson Univ.; Clemson Univ.; St. Cloud State Univ. email@example.com
Depending on the island to which they return, postlarvae of the climbing gobiid fish, Sicyopterus stimpsoni, encounter different environments when they enter freshwater to migrate to upstream breeding habitats after their oceanic larval phase. Streams on Hawai’i have waterfalls nearshore, placing a premium on climbing performance; in contrast, streams on Kaua’i have long, low-gradient stretches below waterfalls, placing a premium on evading non-climbing predators. Our previous work showed that climbing and predation impose selection favoring contrasting body shapes (streamlined for climbing, tall for predator evasion). Also, fish returning to each island have shapes advantageous for the main pressure they encounter. Do such shape differences lead to performance differences that could form the basis for selection in nature? We filmed postlarvae from both islands to compare climbing kinematics, speed, and success rate. S. stimpsoni from Kaua’i are slower during single climbing cycles than S. stimpsoni from Hawai’i. However, longer (20 cm) trials that included rest periods showed no difference in net speed, because fish from Kaua’i rested less. One factor that may contribute to slower climbing movements in Kaua’i fish is that, with narrower heads, their oral sucker expands only one third as much as in Hawai’i fish, possibly limiting body advancement while this sucker is attached to the substrate. Such kinematic and performance differences may contribute to the lower success rate observed for Kaua’i (50%) versus Hawai’i fish (70%) in climbing trials over 2.4 m (100 BL) distances. NSF IOS-0817794, IOS-0817911.