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1. Ontogenetic transitions, biomechanical trade-offs and macroevolution of scyphozoan medusae swimming patterns

   https://doi.org/10.1038/s41598-023-34927-w  

   von Montfort, Guilherme M.; Costello, John H.; Colin, Sean P.; Morandini, André C.; Migotto, Alvaro E.; Maronna, Maximiliano M.; Reginato, Marcelo; Miyake, Hiroshi; Nagata, Renato M. (December 2023, Scientific Reports)

   Abstract Ephyrae, the early stages of scyphozoan jellyfish, possess a conserved morphology among species. However, ontogenetic transitions lead to morphologically different shapes among scyphozoan lineages, with important consequences for swimming biomechanics, bioenergetics and ecology. We used high-speed imaging to analyse biomechanical and kinematic variables of swimming in 17 species of Scyphozoa (1 Coronatae, 8 “Semaeostomeae” and 8 Rhizostomeae) at different developmental stages. Swimming kinematics of early ephyrae were similar, in general, but differences related to major lineages emerged through development. Rhizostomeae medusae have more prolate bells, shorter pulse cycles and higher swimming performances. Medusae of “Semaeostomeae”, in turn, have more variable bell shapes and most species had lower swimming performances. Despite these differences, both groups travelled the same distance per pulse suggesting that each pulse is hydrodynamically similar. Therefore, higher swimming velocities are achieved in species with higher pulsation frequencies. Our results suggest that medusae of Rhizostomeae and “Semaeostomeae” have evolved bell kinematics with different optimized traits, rhizostomes optimize rapid fluid processing, through faster pulsations, while “semaeostomes” optimize swimming efficiency, through longer interpulse intervals that enhance mechanisms of passive energy recapture. 

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2. Fluid mechanics of feeding determine the trophic niche of the hydromedusa Clytia gregaria

   https://doi.org/10.1002/lno.11653  

   Corrales‐Ugalde, Marco; Sutherland, Kelly R. (December 2020, Limnology and Oceanography)

   Abstract Phenotypic features define feeding selectivity in planktonic predators and therefore determine energy flow through food webs. In current‐feeding cnidarian hydromedusae, swimming and predation are coupled such that swimming also brings prey into contact with feeding structures. Fluid mechanical disturbances may initiate escape responses by flow‐sensing prey. Previous studies have not considered how fluid signals define the trophic niche of current‐feeding gelatinous predators. We used the hydromedusaClytia gregariato determine (1) how passive (sinking) and active (swimming) feeding behavior affects pre‐encounter responses of prey to the medusae‐induced fluid motion, and (2) how prey responses affect the medusae's ingestion efficiencies. Videography of the predation process showed that passive prey such as invertebrate larvae were ingested during both feeding behaviors, whereas flow‐sensing prey such as copepods escaped the predator's active feeding behavior, but were unable to detect the predator's passive sinking behavior and were ingested (KWX²= 19.8246, df = 4,p < 0.001). Flow visualizations using particle image velocimetry (PIV) showed fluid deformation values during passive feeding below threshold values that trigger escape responses of copepods. To address whether fluid signals mediate prey capture, we compared fluid signals produced by three hydromedusae with different diets.Aequorea victoriaandMitrocoma cellulariaproduced higher deformation thanC. gregaria(two‐way ANOVA,F_2,52= 5.532,p= 0.007), which explains their previously documented negative selection for flow‐sensing prey like copepods. Through the analysis of hydromedusan feeding behaviors and pre‐encounter prey escapes, we provide evidence that fluid signatures shape the trophic niches of gelatinous predators. 

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3. Coevolution of the Tlx homeobox gene with medusa development (Cnidaria: Medusozoa)

   https://doi.org/10.1038/s42003-023-05077-6  

   Travert, Matthew; Boohar, Reed; Sanders, Steven M.; Boosten, Manon; Leclère, Lucas; Steele, Robert E.; Cartwright, Paulyn (July 2023, Communications Biology)

   Abstract Cnidarians display a wide diversity of life cycles. Among the main cnidarian clades, only Medusozoa possesses a swimming life cycle stage called the medusa, alternating with a benthic polyp stage. The medusa stage was repeatedly lost during medusozoan evolution, notably in the most diverse medusozoan class, Hydrozoa. Here, we show that the presence of the homeobox geneTlxin Cnidaria is correlated with the presence of the medusa stage, the gene having been lost in clades that ancestrally lack a medusa (anthozoans, endocnidozoans) and in medusozoans that secondarily lost the medusa stage. Our characterization ofTlxexpression indicate an upregulation ofTlxduring medusa development in three distantly related medusozoans, and spatially restricted expression patterns in developing medusae in two distantly related species, the hydrozoanPodocoryna carneaand the scyphozoanPelagia noctiluca. These results suggest thatTlxplays a key role in medusa development and that the loss of this gene is likely linked to the repeated loss of the medusa life cycle stage in the evolution of Hydrozoa. 

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4. Hydrodynamics of Vortex Generation during Bell Contraction by the Hydromedusa Eutonina indicans (Romanes, 1876)

   https://doi.org/10.3390/biomimetics4030044  

   Costello, John H.; Colin, Sean P.; Gemmell, Brad J.; Dabiri, John O. (September 2019, Biomimetics)

   Swimming bell kinematics and hydrodynamic wake structures were documented during multiple pulsation cycles of a Eutonina indicans (Romanes, 1876) medusa swimming in a predominantly linear path. Bell contractions produced pairs of vortex rings with opposite rotational sense. Analyses of the momentum flux in these wake structures demonstrated that vortex dynamics related directly to variations in the medusa swimming speed. Furthermore, a bulk of the momentum flux in the wake was concentrated spatially at the interfaces between oppositely rotating vortices rings. Similar thrust-producing wake structures have been described in models of fish swimming, which posit vortex rings as vehicles for energy transport from locations of body bending to regions where interacting pairs of opposite-sign vortex rings accelerate the flow into linear propulsive jets. These findings support efforts toward soft robotic biomimetic propulsion. 

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5. Distributed propulsion enables fast and efficient swimming modes in physonect siphonophores

   https://doi.org/10.1073/pnas.2202494119  

   Du Clos, Kevin T.; Gemmell, Brad J.; Colin, Sean P.; Costello, John H.; Dabiri, John O.; Sutherland, Kelly R. (December 2022, Proceedings of the National Academy of Sciences)

   Many fishes employ distinct swimming modes for routine swimming and predator escape. These steady and escape swimming modes are characterized by dramatically differing body kinematics that lead to context-adaptive differences in swimming performance. Physonect siphonophores, such as Nanomia bijuga , are colonial cnidarians that produce multiple jets for propulsion using swimming subunits called nectophores. Physonect siphonophores employ distinct routine and steady escape behaviors but–in contrast to fishes–do so using a decentralized propulsion system that allows them to alter the timing of thrust production, producing thrust either synchronously (simultaneously) for escape swimming or asynchronously (in sequence) for routine swimming. The swimming performance of these two swimming modes has not been investigated in siphonophores. In this study, we compare the performances of asynchronous and synchronous swimming in N. bijuga over a range of colony lengths (i.e., numbers of nectophores) by combining experimentally derived swimming parameters with a mechanistic swimming model. We show that synchronous swimming produces higher mean swimming speeds and greater accelerations at the expense of higher costs of transport. High speeds and accelerations during synchronous swimming aid in escaping predators, whereas low energy consumption during asynchronous swimming may benefit N. bijuga during vertical migrations over hundreds of meters depth. Our results also suggest that when designing underwater vehicles with multiple propulsors, varying the timing of thrust production could provide distinct modes directed toward speed, efficiency, or acceleration. 

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