Aquatic bladderworts ( To understand what makes suction feeding possible on the small scale of bladderwort traps, we characterised their suction flows experimentally (using particle image velocimetry) and mathematically (using computational fluid dynamics and analytical mathematical models). We show that bladderwort traps avoid the adverse effects of creeping flow by generating strong, fast‐onset suction pressures. Our findings suggest that traps use three morphological adaptations: the trap walls' fast release of elastic energy ensures strong and constant suction pressure; the trap door's fast opening ensures effectively instantaneous onset of suction; the short channel leading into the trap ensures undeveloped flow, which maintains a wide effective channel diameter. Bladderwort traps generate much stronger suction flows than larval fish with similar gape sizes because of the traps' considerably stronger suction pressures. However, bladderworts' ability to generate strong suction flows comes at considerable energetic expense.
The carnivorous plant bladderwort exemplifies the use of accumulated elastic energy to power motion: respiration-driven pumps slowly load the walls of its suction traps with elastic energy (∼1 h). During a feeding strike, this energy is released suddenly to accelerate water (∼1 ms). However, due to the traps’ small size and concomitant low Reynolds number, a significant fraction of the stored energy may be dissipated as viscous friction. Such losses and the mechanical reversibility of Stokes flow are thought to degrade the feeding success of other suction feeders in this size range, such as larval fish. In contrast, triggered bladderwort traps are generally successful. By mapping the energy budget of a bladderwort feeding strike, we illustrate how this smallest of suction feeders can perform like an adult fish.
more » « less- NSF-PAR ID:
- 10119030
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Integrative and Comparative Biology
- Volume:
- 59
- Issue:
- 6
- ISSN:
- 1540-7063
- Page Range / eLocation ID:
- p. 1597-1608
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Utricularia gibba and U .australis ) capture zooplankton in mechanically triggered underwater traps. With characteristic dimensions less than 1 mm, the trapping structures are among the smallest known to capture prey by suction, a mechanism that is not effective in the creeping‐flow regime where viscous forces prevent the generation of fast and energy‐efficient suction flows. -
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Abstract The aquatic bladderwort
Utricularia gibba captures zooplankton in mechanically triggered underwater traps. With characteristic dimensions <1 mm, the trapping structures are among the smallest known that work by suction—a mechanism that would not be effective in the creeping‐flow regime. To understand the adaptations that make suction feeding possible on this small scale, we have measured internal flow speeds during artificially triggered feeding strikes in the absence of prey. These data are compared with complementary analytical models of the suction event: an inviscid model of the jet development in time and a steady‐state model incorporating friction. The initial dynamics are well described by a time‐dependent Bernoulli equation in which the action of the trap door is represented by a step increase in driving pressure. According to this model, the observed maximum flow speed (5.2 m/s) depends only on the pressure difference, whereas the initial acceleration (3 × 104 m/s2) is determined by pressure difference and channel length. Because the terminal speed is achieved quickly (~0.2 ms) and the channel is short, the remainder of the suction event (~2.0 ms) is effectively an undeveloped viscous steady state. The steady‐state model predicts that only 17% of power is lost to friction. The energy efficiency and steady‐state fluid speed decrease rapidly with decreasing channel diameter, setting a lower limit on practical bladderwort size. -
null (Ed.)Abstract Suction feeding has evolved independently in two highly disparate animal and plant systems, aquatic vertebrates and carnivorous bladderworts. We review the suction performance of animal and plant suction feeders to explore biomechanical performance limits for aquatic feeders based on morphology and kinematics, in the context of current knowledge of suction feeding. While vertebrates have the greatest diversity and size range of suction feeders, bladderworts are the smallest and fastest known suction feeders. Body size has profound effects on aquatic organismal function, including suction feeding, particularly in the intermediate flow regime that tiny organisms can experience. A minority of tiny organisms suction feed, consistent with model predictions that generating effective suction flow is less energetically efficient and also requires more flow-rate specific power at small size. Although the speed of suction flows generally increases with body and gape size, some specialized tiny plant and animal predators generate suction flows greater than those of suction feeders 100 times larger. Bladderworts generate rapid flow via high-energy and high-power elastic recoil and suction feed for nutrients (relying on photosynthesis for energy). Small animals may be limited by available muscle energy and power, although mouth protrusion can offset the performance cost of not generating high suction pressure. We hypothesize that both the high energetic costs and high power requirements of generating rapid suction flow shape the biomechanics of small suction feeders, and that plants and animals have arrived at different solutions due in part to their different energy budgets.more » « less
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null (Ed.)Synopsis In ray-finned fishes, the sternohyoideus (SH) is among the largest muscles in the head region and, based on its size, can potentially contribute to the overall power required for suction feeding. However, the function of the SH varies interspecifically. In largemouth bass (Micropterus salmoides) and several clariid catfishes, the SH functions similarly to a stiff ligament. In these species, the SH remains isometric and transmitts power from the hypaxial musculature to the hyoid apparatus during suction feeding. Alternatively, the SH can shorten and contribute muscle power during suction feeding, a condition observed in the bluegill sunfish (Lepomis macrochirus) and one clariid catfish. An emerging hypothesis centers on SH muscle size as a predictor of function: in fishes with a large SH, the SH shortens during suction feeding, whereas in fish with a smaller SH, the muscle may remain isometric. Here, we studied striped surfperch (Embiotoca lateralis), a species in which the SH is relatively large at 8.8% of axial muscle mass compared with 4.0% for L. macrochirus and 1.7% for M. salmoides, to determine whether the SH shortens during suction feeding and is, therefore, bifunctional—both transmitting and generating power—or remains isometric and only transmits power. We measured skeletal kinematics of the neurocranium, urohyal, and cleithrum with Video Reconstruction of Moving Morphology, along with muscle strain and shortening velocity in the SH and epaxial muscles, using a new method of 3D external marker tracking. We found mean SH shortening during suction feeding strikes (n = 22 strikes from four individual E. lateralis) was 7.2 ± 0.55% (±SEM) of initial muscle length. Mean peak speed of shortening was 4.9 ± 0.65 lengths s−1, and maximum shortening speed occurred right around peak gape when peak power is generated in suction feeding. The cleithrum of E. lateralis retracts and depresses but the urohyal retracts and depresses even more, a strong indicator of a bifunctional SH capable of not only generating its own power but also transmitting hypaxial power to the hyoid. While power production in E. lateralis is still likely dominated by the axial musculature, since even the relatively large SH of E. lateralis is only 8.8% of axial muscle mass, the SH may contribute a meaningful amount of power given its continual shortening just prior to peak gape across all strikes. These results support the finding from other groups of fishes that a large SH muscle, relative to axial muscle mass, is likely to both generate and transmit power during suction feeding.more » « less
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Abstract The axial musculature of fishes has historically been characterized as the powerhouse for explosive swimming behaviors. However, recent studies show that some fish also use their ‘swimming’ muscles to generate over 90% of the power for suction feeding. Can the axial musculature achieve high power output for these two mechanically distinct behaviors? Muscle power output is enhanced when all of the fibers within a muscle shorten at optimal velocity. Yet, axial locomotion produces a mediolateral gradient of muscle strain that should force some fibers to shorten too slowly and others too fast. This mechanical problem prompted research into the gearing of fish axial muscle and led to the discovery of helical fiber orientations that homogenize fiber velocities during swimming, but does such a strain gradient also exist and pose a problem for suction feeding? We measured muscle strain in bluegill sunfish,
Lepomis macrochirus, and found that suction feeding produces a gradient of longitudinal strain that, unlike the mediolateral gradient for locomotion, occurs along the dorsoventral axis. A dorsoventral strain gradient within a muscle with fiber architecture shown to counteract a mediolateral gradient suggests that bluegill sunfish should not be able to generate high power outputs from the axial muscle during suction feeding—yet prior work shows that they do, up to 438 W kg−1. Solving this biomechanical paradox may be critical to understanding how many fishes have co-opted ‘swimming’ muscles into a suction feeding powerhouse.
