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1. The evolution of siphonophore tentilla for specialized prey capture in the open ocean

   https://doi.org/10.1073/pnas.2005063118  

   Damian-Serrano, Alejandro; Haddock, Steven H.; Dunn, Casey W. (February 2021, Proceedings of the National Academy of Sciences)

   null (Ed.)

   Predator specialization has often been considered an evolutionary “dead end” due to the constraints associated with the evolution of morphological and functional optimizations throughout the organism. However, in some predators, these changes are localized in separate structures dedicated to prey capture. One of the most extreme cases of this modularity can be observed in siphonophores, a clade of pelagic colonial cnidarians that use tentilla (tentacle side branches armed with nematocysts) exclusively for prey capture. Here we study how siphonophore specialists and generalists evolve, and what morphological changes are associated with these transitions. To answer these questions, we: a) Measured 29 morphological characters of tentacles from 45 siphonophore species, b) mapped these data to a phylogenetic tree, and c) analyzed the evolutionary associations between morphological characters and prey-type data from the literature. Instead of a dead end, we found that siphonophore specialists can evolve into generalists, and that specialists on one prey type have directly evolved into specialists on other prey types. Our results show that siphonophore tentillum morphology has strong evolutionary associations with prey type, and suggest that shifts between prey types are linked to shifts in the morphology, mode of evolution, and evolutionary correlations of tentilla and their nematocysts. The evolutionary history of siphonophore specialization helps build a broader perspective on predatory niche diversification via morphological innovation and evolution. These findings contribute to understanding how specialization and morphological evolution have shaped present-day food webs. 

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2. Effects of prey capture on the swimming and feeding performance of choanoflagellates

   https://doi.org/10.1017/flo.2023.16  

   Nguyen, H; Ross, E; Cortez, R; Fauci, L; Koehl, MAR (January 2023, Flow)

   Locomoting organisms often carry loads such as captured prey or young. Load-carrying effects on high-Reynolds-number flight have been studied, but the fluid dynamics of load carrying by low-Reynolds-number microorganisms has not. We studied low-Reynolds-number load carrying using unicellular choanoflagellates, which wave a flagellum to swim and create a water current transporting bacterial prey to a food-capturing collar of microvilli. A regularized Stokeslet framework was used to model the hydrodynamics of a swimming choanoflagellate with bacterial prey on its collar. Both the model and microvideography of choanoflagellates showed that swimming speed decreases as number of prey being carried increases. Flux of water into the capture zone is reduced by bacteria on the collar, which redirect the water flow and occlude parts of the collar. Feeding efficiency (prey captured per work to produce the feeding current) is decreased more by large prey, prey in the plane of flagellar beating and prey near microvillar tips than by prey in other locations. Some choanoflagellates can attach themselves to surfaces. We found that the reduction in flux due to bacterial prey on the collars of these attached thecate cells was similar to the reduction in flux for swimmers. 

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3. External power amplification drives prey capture in a spider web

   https://doi.org/10.1073/pnas.1821419116  

   Han, S. I.; Astley, H. C.; Maksuta, D. D.; Blackledge, T. A. (June 2019, Proceedings of the National Academy of Sciences)

   Power amplification allows animals to produce movements that exceed the physiological limits of muscle power and speed, such as the mantis shrimp’s ultrafast predatory strike and the flea’s jump. However, all known examples of nonhuman, muscle-driven power amplification involve anatomical structures that store energy from a single cycle of muscular contraction. Here, we describe a nonhuman example of external power amplification using a constructed device: the web of the triangle-weaver spider, Hyptiotes cavatus , which uses energy stored in the silk threads to actively tangle prey from afar. Hyptiotes stretches its web by tightening a separate anchor line over multiple cycles of limb motion, and then releases its hold on the anchor line when insects strike the web. Both spider and web spring forward 2 to 3 cm with a peak acceleration of up to 772.85 m/s 2 so that up to four additional adhesive capture threads contact the prey while jerking caused by the spider’s sudden stop subsequently wraps silk around the prey from all directions. Using webs as external “tools” to store energy offers substantial mechanical advantages over internal tissue-based power amplification due to the ability of Hyptiotes to load the web over multiple cycles of muscular contraction and thus release more stored energy during prey capture than would be possible with muscle-driven anatomical elastic-energy systems. Elastic power amplification is an underappreciated component of silk’s function in webs and shows remarkable convergence to the fundamental mechanical advantages that led humans to engineer power-amplifying devices such as catapults and ballistae. 

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4. Mechanics of the Prey Capture Technique of the South African Grassland Bolas Spider, Cladomelea akermani

   https://doi.org/10.3390/insects13121118  

   Diaz, Candido; Roff, John (December 2022, Insects)

   Spiders use various combinations of silks, adhesives, and behaviors to ensnare prey. One common but difficult-to-catch prey is moths. They easily escape typical orb-webs because their bodies are covered in tiny sacrificial scales that flake off when in contact with the web’s adhesives. This defense is defeated by spiders of the sub-family of Cyrtarachninae—moth-catching specialists who combine changes in orb-web structure, predatory behavior, and chemistry of the aggregate glue placed in those webs. The most extreme changes in web structure are shown by the bolas spiders which create only one or two glue droplets at the end of a single thread. They prey on male moths by releasing pheromones to draw them close. Here, we confirm the hypothesis that the spinning behavior of the spider is directly used to spin its glue droplets using a high-speed video camera to observe the captured behavior of the bolas spider Cladomelea akermani as it actively spins its body and bolas. We use the kinematics of the spider and bolas to begin to quantify and model the physical and mechanical properties of the bolas during prey capture. We then examine why this species chooses to spin its body, an energetically costly behavior, during prey capture. We test the hypothesis that spinning helps to spread pheromones by creating a computational fluid dynamics model of airflow within an open field and comparing it to that of airflow within a tree, a common environment for bolas spiders that do not spin. Spinning in an open environment creates turbulent air, spreading pheromones further and creating a pocket of pheromones. Conversely, spinning within a tree does little to affect the natural airflow. 

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5. High prey capture efficiencies of oceanic epipelagic lobate and cestid ctenophores

   https://doi.org/10.1093/plankt/fbae044  

   Child, Taylor; Costello, John H; Gemmell, Brad J; Sutherland, Kelly R; Colin, Sean P (September 2024, Journal of Plankton Research)

   Koski, Marja (Ed.)

   Abstract Ctenophores are numerically dominant members of oceanic epipelagic communities around the world. The ctenophore community is often comprised of several common, co-occurring lobate and cestid genera. Previous quantifications of the amount of fluid that lobate ctenophores entrain in their feeding currents revealed that oceanic lobates have the potential for high feeding rates. In order to more directly examine the trophic role of oceanic lobate ctenophores, we quantified the encounter and retention efficiencies of several co-occurring species (Bolinopsis vitrea, Ocyropsis crystallina, Eurhamphea vexilligera and Cestum veneris) in their natural environments. Encounters and predator–prey interactions were video recorded in the field using specialized cameras and SCUBA techniques. The lobate species encountered, on average, 2.4 prey per minute and ingested 40% of these prey. This translated to an estimated ingestion rate of close to 1 prey per minute. Cestum veneris and most of the lobate species retained prey as efficiently as the voracious coastal lobate predator Mnemiopsis leidyi, suggesting that these oceanic species have a similar predation impact in their environments as M. leidyi does in coastal ecosystems. Hence, quantified in situ predatory-prey interactions indicate that epipelagic ctenophores have a significant impact on oceanic ecosystems worldwide. 

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