Morphology, Swimming Performance and Propulsive Mode of Six Co-occurring Hydromedusae

Jet propulsion, based on examples from the Hydrozoa, has served as a valuable model for swimming by medusae. However, cnidarian medusae span several taxonomic classes (collectively known as the Medusazoa) and represent a diverse array of morphologies and swimming styles. Does one mode of propulsion appropriately describe swimming by all medusae? This study examined a group of co-occurring hydromedusae collected from the waters of Friday Harbor, WA, USA, to investigate relationships between swimming performance and underlying mechanisms of thrust production. The six species examined encompassed a wide range of bell morphologies and swimming habits. Swimming performance (measured as swimming acceleration and velocity) varied widely among the species and was positively correlated with bell streamlining (measured as bell fineness ratio) and velar structure development (measured as velar aperture ratio). Calculated thrust production due to jet propulsion adequately explained acceleration patterns of prolate medusae (Aglantha digitale, Sarsia sp. and Proboscidactyla flavicirrata) possessing well-developed velums. However, acceleration patterns of oblate medusae (Aequorea victoria, Mitrocoma cellularia and Phialidium gregarium) that have less developed velums were poorly described by jet thrust production. An examination of the wakes behind swimming medusae indicated that, in contrast to the clearly defined jet structures produced by prolate species, oblate medusae did not produce defined jets but instead produced prominent vortices at the bell margins. These vortices are consistent with a predominantly drag-based, rowing mode of propulsion by the oblate species. These patterns of propulsive mechanics and swimming performance relate to the role played by swimming in the foraging ecology of each medusa. These patterns appear to extend beyond hydromedusae and thus have important implications for other members of the Medusazoa

Functional Characteristics of Nematocysts Found on the Scyphomedusa Cyanea Capillata

Although prey capture by cnidarians is mediated through nematocysts, their influence on prey selection by cnidarians remains poorly documented. The difficulty in visualizing nematocyst–prey interactions remains the chief obstacle to understanding how the wide variety of nematocyst types influences the mechanics of prey capture. One solution to this limitation has been to assign functional roles to nematocysts based on morphological characters of discharged cnidae. Here we report results of an alternative approach based upon dynamic traits of nematocyst discharge. We examined tubule lengths, tubule discharge velocities and net-to-gross displacement ratios of tubules of discharging nematocysts possessed by the cosmopolitan scyphomedusa, Cyanea capillata. This nematocyst assemblage consisted of euryteles, birhopaloids and three different isorhizas — a-isorhizas, A-isorhizas and O-isorhizas. Dynamic traits varied little within each nematocyst type but there were significant differences between the different types. Most importantly, dynamic traits varied significantly within a broad category of nematocyst – the isorhizas – indicating that conventional classification schemes that infer function based on broad nematocyst categories may not appropriately describe the functional roles of these nematocysts. The dynamic properties of discharging nematocysts were consistent with physical results described in studies using scanning electron microscopy images of nematocyst–prey interactions. These data suggest that nematocysts vary significantly in their roles during predation, but that inferences relating prey selection with broad nematocyst categories merit careful examination

Prey Resource Utilization by Coexistent Hydromedusae from Friday Harbor, Washington, USA

Prey selection patterns were quantified for a sympatric group of hydromedusae from Friday Harbor, WA. Selection patterns varied between species, but were largely replicable between sample dates and resembled dietary patterns found in similar studies from neighboring regions. Ambush-foraging medusae (Aglantha digitale, Sarsia tubulosa, and Proboscidactyla flavicirrata) fed primarily on crustacean and ciliated prey but the dietary niches of these hydromedusan species centered on different fractions of the available plankton. Consequently, little dietary overlap occurred between the ambush foraging hydromedusae. In contrast, the dietary niches of cruising predators (Aequorea victoria, Mitrocoma cellularia, and Phialidium gregarium) overlapped substantially because those species all fed on similar soft-bodied prey such as eggs and appendicularians. These results have two important implications for trophic patterns involving medusae. First, different mechanisms of prey encounter and capture used by hydromedusae (ambush vs. cruising patterns) result in important interspecific dietary differences and, hence, trophic roles of the medusae. Second, whereas cruising medusae may consume similar prey and hence form a feeding guild, ambush-foraging medusae may experience substantially less prey overlap and, for the community examined here, do not experience potentially strong feeding competition from other medusan species

Meson Production at COSY-TOF and COSY-ANKE

The roles of the COSY-TOF and COSY-ANKE spectrometers in the measurement of strange meson production are briefly reviewed, mainly in connection with new results on the pp -> K^+ p Lambda, pp -> K^+ p Sigma^0 and pp -> K^+ n Sigma^+ reactions.Comment: Invited talk at the MESON2010 conference in Krakow, June 201

A Method for the Perceptual Optimization of Complex Visualizations

A common problem in visualization applications is the display of one surface overlying another. Unfortunately, it is extremely difficult to do this clearly and effectively. Stereoscopic viewing can help, but in order for us to be able to see both surfaces simultaneously, they must be textured, and the top surface must be made partially transparent. There is also abundant evidence that all textures are not equal in helping to reveal surface shape, but there are no general guidelines describing the best set of textures to be used in this way. What makes the problem difficult to perceptually optimize is that there are a great many variables involved. Both foreground and background textures must be specified in terms of their component colors, texture element shapes, distributions, and sizes. Also to be specified is the degree of transparency for the foreground texture components. Here we report on a novel approach to creating perceptually optimal solutions to complex visualization problems and we apply it to the overlapping surface problem as a test case. Our approach is a three-stage process. In the first stage we create a parameterized method for specifying a foreground and background pair of textures. In the second stage a genetic algorithm is applied to a population of texture pairs using subject judgments as a selection criterion. Over many trials effective texture pairs evolve. The third stage involves characterizing and generalizing the examples of effective textures. We detail this process and present some early results

In Honor of Matthew Rabin: Winner of the John Bates Clark Medal

Although there is some evidence that Matthew Rabin existed before 1990, we had the pleasure of discovering him for ourselves when, in the early 1990s, he sent each of us a copy of his manuscript "Incorporating Fairness into Game Theory and Economics" [2]. Matthew was, at this time, an assistant professor in Berkeley's economics department, having recently finished his graduate training at MIT. The paper was remarkable in many ways, and it induced us both to call around and ask: "Who is this guy Rabin?" Now, just a decade later, we find ourselves writing an article in honor of his winning the John Bates Clark award. So, who is this guy

Proposition 13 and the California Fiscal Shell Game

We study the effects of California’s tax and expenditure limitations, especially Proposition 13. We find that Proposition 13 was indeed effective at reducing both ad valorem property taxes per capita and total state and local taxes per capita, at least in the short run. We further argue that there have been unintended second- ary effects that have resulted in an increased tax burden, undermining the aims of Proposition 13. To circumvent the limits imposed by Proposition 13, the state has drastically increased nonguaranteed debt, has privatized the public fisc, and has devolved the authority to lay and collect taxes and to spend the proceeds so gained. The devolution of authority has been among the swiftest growing aspects of government finance in California, to a far greater extent than in other states. Lastly, we argue that the new tax and spending authorities that have been created to circumvent Proposition 13 have led to a reduction in government transparency and accountability and pose an increasing threat to our democracy

Non-linear stability of vortex formation in swarms of interacting particles

We use a particle-based model of a swarm of interacting particles to explore analytically the conditions for the formation of vortexlike behavior. Our model uses pairwise interaction potentials to model weak long-range attraction and strong short-range repulsion with a dissipation function to align particle velocity vectors. We use the effective energy of the swarm as a Lyapunov function to prove convergence to a vortexlike state. Our analysis extends previous work which has relied purely on simulation to explore the formation and stability of vortexlike behavior through analytical rather than numerical methods

Cheating on Their Taxes: When Are Tax Limitations Effective at Limiting State Taxes, Expenditures, and Budgets?

At a Seminar arranged by the Ecological Research Committee on October 30 , 1967, Dr. Svante Odén discussed the acidity and sulphur conditions over Europe and the consequensos to soils, surfaco waters and biological systems. In 1952 a European network of stations for atmospheric chemistry was organized by the International Meteorological Institute , Stockholm (Fig. 1). Odén and Dr. Torsten Ahl, Uppsala, later complemented the network in Scandinavia with stations for surface water chemistry (Fig. 3). At the atmospheric chemical network measurements of different element s havc been made for about 15 years. Changes of the atmospheric chemical climate can now be evaluated from the dat a, showing either positive or negative trends (Fig. 2 , 20 and 21). The sulphur content of air (Fig. 18) and of precipitation (Fig. 17 ) shows a characteristic pattern for Europe, indicating a close rolationship to air pollution from citiesand industrios. The rising sulphur content in the atmosphere are undoubtedly connected with the incrcasing use of sulphurous f'uels as a suostitute for coke and coal. The increasing addition of sulphur compounds t o the atmosphere (mainly as SO2 and H2S ) leads to an incrcase of the acidity o f the precipitation. Monthly data from threc stations conccrning pH are given (Fig. 4 , 5 and 6) . With a few exceptions the pH valuos at the network stations are dccrcasing with time (Fig. 9, 10 and 11) . The ratc of decrcasc of the 1) Department of Pedology, Agricultural College of Sweden, Uppsala 2) Swedish Natural Science Research Council , Sveavägen 166, Stockholm 23 pH values shows a geographical distribution pattern (Fig. 12), which can be expected from the intensity of industrial activities. The acidity of the yearly precipitation in Europe is mapped for 1958 (Fig. 13) , 1962 (Fig. 14) and 1965 (Fig. 15). In 1958 values below pH 5 were to be found only in a limited area over The Netherlands. As is shown on the succceding maps, this area has since spread over Central Europe. The other acid zones are also procecding and in 1965 the isoline for pH 4.5 had reached the Southern part of Sweden. In 1967 the pH values for Central Sweden had decreased to approx. 4.3. A study of the wind trajectories (Fig. 8) shows, that this low pH value is partly a result of a transport of air pollutants from source to sink areas. "The Scandinavian Sulphur Depression" (Fig. 2 2) indicates that a complicated hydrometeorological mechanism is involved in the distributional pattern. In 1965 almost a thousand Scandinavian lake and river waters were chemically investigatcd by Ahl and Odén. For considerable areas the pH-values were found to be so low as to affect fish life. The mapping of pH (Fig. 2 5 ) corresponds with that for Magnesium (Fig. 26) indicating a depletion of eations of the soil complex .. This is also reflected by thc long term changes of the concentration af anions ( so4) and cations (Ca) in river systems (Fig. 27 a and b). Last summer a special study o f the acidity of 600 lakes in Western Scandinavia was made by Dr. E . Eriksson. The results showed that since 1959 the pH-values have boen reduced on an average by 0.4 units. The acid precipitation will sooner or later acidify the river systers. The change in pH will depend, among others, on the buffer capacity of the catchment area. However, negative trends have already appeared in both large river systems (Fig. 23) and small ones (Fig. 24). The acidification of natural waters can be a threat to aquatic life. Organisms cannot normally exist in water with pH-values below 4.0. Certain valuable fish, such as salmon, are threatened at pH 5.5 and the catch of salrnon in Mörrumsån is continuously decreasing (Fig. 28 ). Soils may also be affected if the supply of nautralizing alkalis are depleted or poor. An impoverished forest arowth rate could be the result (Fig. 30). The important point is, according to Odén, that the balance of nature is considerably disturbed by the present atmospheric pollution of sulphuric acid and other acidifying compounds such as nitric and hydrochloric acid. An atmospheric chemical atlas of Europe containing data on air as well as precipitation is being prepared on the basis of existing data. * * * In the discussion that followed Odéns paper f'urther evidence of extensive fish kill in acid waters was given. Two speakers emphasized the economic aspects of the heavy damage that is caused each year by acid corrosion of metals, now amounting to 2 % of our gross national product, and the economic as well as cultural valuecs that are lost by the deterioration of buildnings and stone ornaments