Adhesive force and endurance during waterfall climbing in an amphidromous gobiid, Sicyopterus japonicus (Teleostei: Gobiidae): Ontogenetic scaling of novel locomotor performance

Abstract

An amphidromous sicydiine goby, Sicyopterus japonicus, exhibits rock-climbing behavior during upstream migration along rivers and streams. Using a pelvic sucker formed by fused pelvic fins, S. japonicus generates suction adhesion on the climbing surface. By measuring performance variables that correlate with successful rock-climbing capability, we evaluated scaling relationships of adhesive suction force generated by the pelvic sucker and fatigue during climbing in S. japonicus during ontogeny. In continuous climbing on the experimental 60°-inclined surface, the pelvic sucker of S. japonicus exhibited strong positive allometry in generating suction force for adhesion during ontogeny. In contrast, fatigue time of the pelvic sucker muscles for sustained adhesion scaled non-linearly with body mass during ontogeny. In addition, fatigue time and body mass showed the best fit to a quadratic regression, which predicted intermediate-sized individuals (large juveniles to small adults) to have better performance in adhesive endurance than smaller or larger individuals. Our experimental results indicate that different sizes of waterfall-climbing gobies have different performance capacities for rock climbing perhaps because of physiological differences in their pelvic muscles. In addition, our data from S. japonicus indicates that selection pressures on the locomotor capacities of waterfall-climbing gobiids vary during ontogeny.