| TESTING THE “MORPHOGENESIS-IMPROVES-PERFORMANCE” MODEL OF ESCAPE-RESPONSE PERFORMANCE IN TELEOST FISHES |
| GIBB, A.C., Northern Arizona University, Flagstaff, AZ, USA, 86011, alice.gibb@nau.edu; Ferry-Graham, L.A., Moss Landing Marine Laboratories, Moss Landing, CA, USA, 95039, lfgraham@mlml.calstate.edu |
| In juvenile and adult fishes, escape response performance as measured by maximum swimming speed (m/s) increases linearly with body size; however, as fish grow larger they take longer to reach their maximum swimming speed and their length-specific velocity (total lengths/s) declines. In contrast, during larval development, fish become both absolutely and relatively faster in all aspects of escape performance. One hypothesis that attempts to explain this pattern is that the acquisition of key morphological features during development improves escape performance across larval development. However, once juvenile morphology is achieved, performance declines because increases in the cross-sectional area of the axial musculature (length squared) lag behind increases in fish body mass (length cubed). An alternative hypothesis is that fish larvae demonstrate increased swimming performance during early development primarily because the hydrodynamic regime is altered as fish become both larger and faster. In fact, changes in body size and swimming velocity will alter the ratio of inertial to viscous forces acting on the fish, which could cause fish to become more effective at producing escape movements as inertial forces become dominant. We assess these hypotheses by examining escape-response behaviors in juveniles of live-bearing fish species. These fry emerge from their mothers at a very small size (similar in length and mass to many fish larvae), but with juvenile morphology. The “morphogenesis-improves-performance” model predicts that, as fry become larger, escape performance will decline; however, the “hydrodynamic-regime-determines-performance” hypothesis predicts that escape performance will improve as fry grow larger and faster and the viscous effects become subordinate. We find that juvenile live-bearers achieve maximum escape response performance immediately upon parturition, and that these juveniles have a very high length-specific swimming velocity (as would be predicted for a fish with juvenile morphology but a very small body mass). These findings support the general hypothesis that morphogenesis drives performance improvements across development in larval fish and that changes in hydrodynamic regime are less important. We note that the morphogenesis-improves-performance hypothesis has clear implications for the functional ramifications of various life history patterns observed across teleost species. In addition, the relationship between life history pattern and escape performance may help explain a repeatedly observed association between certain life history characteristics in invasive versus imperiled fish species. |
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