Potential for Anthropogenic Fin Damage to Affect Individual Responses to Prey in Bluegill Sunfish (Lepomis macrochirus): A New Hypothesis for Kinematic Studies

In fishes, damage to important morphological structures such as fins through natural damage and anthropogenic factors can have cascading effects on prey capture performance and individual fitness. Bluegill sunfish (Lepomis macrochirus) are a common freshwater species in North America, are a model organism for performance studies, and often experience natural injuries. We opportunistically sampled two populations of fish in the lab to generate a hypothesis for the effect of sub-lethal fin damage resulting from the capture technique on kinematic performance during prey capture in bluegill. We found no statistical differences in mean prey capture kinematics or predator accuracy, but damaged fish used more variable kinematics and more readily struck at non-prey items. We suggest that a reduction in stability and individual consistency occurs as a result of fin damage. This difference could have consequences for higher-order ecological interactions such as competitive ability, despite a lack of apparent performance cost at the individual level, and deserves consideration in future studies of prey capture performance in fish.

Short-range hunters: exploring the function and constraints of water shooting in dwarf gouramis

Ballistic predation is a rare foraging adaptation: in fishes, most attention has focused on a single genus, the archerfish, known to manipulate water to shoot down prey above the water surface. However, several gourami species also exhibit apparently similar 'shooting' behaviour, spitting water up to 5 cm above the surface. In a series of experiments, we explored the shooting behaviour and aspects of its significance as a foraging ability in the dwarf gourami (Trichogaster lalius). We investigated sex differences in shooting abilities to determine whether gourami shooting is related to the sex-specific bubble nest manufacture where males mix air and water at the surface to form bubbles. We found that, actually, both sexes were equally able to shoot and could learn to shoot a novel target. In a second experiment, we presented untrained gouramis with opportunities to shoot at live prey and found they successfully shot down both fruit flies and crickets. Finally, we explored the effect of target height on shooting performance to establish potential constraints of shooting as a foraging ability. The frequency of attempted shots and success of hitting targets decreased with height, whereas latency to shoot increased. We also observed that repeatable individual differences account for variation in these measures of shooting performance. Together, our results provide evidence that gourami shooting has a foraging function analogous to that of archerfish. Gourami shooting may serve as an example of convergent evolution and provide opportunities for comparative studies into the, as yet unexplored, ecology and evolution of shooting in fishes.

Kinematic integration during prey capture varies among individuals but not ecological contexts in bluegill sunfish, Lepomis macrochirus (Perciformes: Centrarchidae)

The general ability of components of an organism to work together to achieve a common goal has been termed integration and is often studied empirically by deconstructing organisms into component parts and quantifying covariation between them. Kinematic traits describing movement are useful for allowing organisms to respond to ecological contexts that vary over short time spans (milliseconds, minutes, etc.). Integration of these traits can contribute to the maintenance of the function of the whole organism, but it is unclear how modulation of component kinematic traits affects their integration. We examined the integration of swimming and feeding during capture of alternative prey types in bluegill sunfish (Lepomis macrochirus). Despite the expected modulation of kinematics, integration within individuals was inflexible across prey types, suggesting functional redundancy for solving a broad constraint. However, integration was variable among individuals, suggesting that individuals vary in their solutions for achieving whole-organism function and that this solution acts as a ‘top-down’ regulator of component traits, which provides insight into why kinematic variation is observed. Additionally, variation in kinematic integration among individuals could serve as an understudied target of environmental selection on prey capture, which is a necessary first step towards the observed divergence in integration among populations and species.

Multifunctional Structures and Multistructural Functions: Integration in the Evolution of Biomechanical Systems

Integration is an essential feature of complex biomechanical systems, with coordination and covariation occurring among and within structural components at time scales that vary from microseconds to deep evolutionary time. Integration has been suggested to both promote and constrain morphological evolution, and the effects of integration on the evolution of structure likely vary by system, clade, historical contingency, and time scale. In this introduction to the 2019 symposium "Multifunctional Structures and Multistructural Functions," we discuss the role of integration among structures in the context of functional integration and multifunctionality. We highlight articles from this issue of Integrative and Comparative Biology that explore integration within and among kinematics, sensory and motor systems, physiological systems, developmental processes, morphometric dimensions, and biomechanical functions. From these myriad examples it is clear that integration can exist at multiple levels of organization that can interact with adjacent levels to result in complex patterns of structural and functional phenotypes. We conclude with a synthesis of major themes and potential future directions, particularly with respect to using multifunctionality, itself, as a trait in evolutionary analyses.