Performance across extreme environments: comparing waterfall climbing among amphidromous gobioid fishes from Caribbean and Pacific Islands
Amphidromous gobioid fishes have colonized streams on tropical and subtropical volcanic islands across the globe. Such streams are often characterized by steep gradients, high velocity currents, and even waterfalls as in-stream obstacles; however, the ability to climb waterfalls has evolved in many goby species, allowing juveniles returning from the ocean to penetrate upstream reaches. Past studies of Hawaiian gobioid fishes have identified two functionally differ - ent climbing techniques that were characterized by differing kinematics: a style described as ‘powerbursting’ among spe - cies with small juveniles (\~1.5 cm body length), and a style described as ‘inching-up’ among species with large juveniles (\~2.2 cm body length). These results suggested a potential size limit to the use of powerburst climbing, and indicated that functional diversity can exist even in extreme environments. In this study, we used standard- and high-speed video to assess kinematic and performance parameters of juvenile and adult Sicydium punctatum from the caribbean island of Dominica, and compared the results with data previously obtained for two species of climbing gobioid fishes from the Hawaiian Island chain, Sicyopterus stimpsoni and Lentipes concolor . Although nearly as large as the ‘inching’ climber S. stimpsoni , climb- ing kinematics of juvenile S. punctatum were similar to those of powerbursting juvenile L. concolor. nonetheless, adults of all three species converged on a climbing style similar to that of the inching-up climber S. stimpsoni , still suggesting a size limit for the powerburst climbing style of L. concolor and S. punctatum. Results of this study provide for a refined understanding of how functional diversity can be maintained in extreme environments across a broad geographic range and taxonomic diversity, and shed light on ontogenetic constraints in locomotor function.