Nematocytes, the stinging cells of cnidarians, are the most evolutionarily ancient venom apparatus. These nanosyringe-like weaponry systems reach pressures of approximately 150 atmospheres before discharging and punching through the outer layer of the prey or predator at accelerations of more than 5 million g, making them one of the fastest biomechanical events known. To gain better understanding of the function of the complex, phylum-specific nematocyst organelle, and its venom payload, we compared the soluble nematocyst's proteome from the sea anemone Anemonia viridis, the jellyfish Aurelia aurita, and the hydrozoan Hydra magnipapillata, each belonging to one of the three basal cnidarian lineages which diverged over 600 Ma. Although the basic morphological and functional characteristics of the nematocysts of the three organisms are similar, out of hundreds of proteins identified in each organism, only six are shared. These include structural proteins, a chaperone which may help maintain venon activity over extended periods, and dickkopf, an enigmatic Wnt ligand which may also serve as a toxin. Nevertheless, many protein domains are shared between the three organisms' nematocyst content suggesting common proteome functionalities. The venoms of Hydra and Aurelia appear to be functionally similar and composed mainly of cytotoxins and enzymes, whereas the venom of the Anemonia is markedly unique and based on peptide neurotoxins. Cnidarian venoms show evidence for functional recruitment, yet evidence for diversification through positive selection, common to other venoms, is lacking. The final injected nematocyst payload comprises a mixture of dynamically evolving proteins involved in the development, maturation, maintenance, and discharge of the nematocysts, which is unique to each organism and potentially to each nematocyst type.

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Summary 1.Temperature and the elemental composition of food are key regulators of consumer growth rate, yet the knowledge on how these factors interact is scarce. In this study, we addressed this issue by using the rotifer Brachionus calyciflorus as a model organism. 2. Rotifers were raised at four different temperatures under a range of C ⁄ P and C ⁄ N ratios in their food and assessed the responses by analysing somatic RNA ⁄ protein ratios as a marker of growth rate. 3. Both N-and P-limited algae restricted the growth rates of rotifers. The interaction between C ⁄ P ratio of a given algae and temperature demonstrated that P limitation became intensified with increasing temperature. 4. Animals that were relieved from N limitation increased their RNA ⁄ protein ratio, as did animals fed on constant C ⁄ N ratio but with P-enriched food. This illustrates a mutual dependency and interaction between N and P in the protein synthesis by up-regulating the biosynthetic machinery, and that even while the effect of N limitation was more pronounced, P limitation was also potentially important in this species. 5. Our results provide evidence that over the tested range of temperature and food qualities, nutrient limitation in these animals was more important than the temperature effect. We also found, however, that increasing temperature can shift from P to N limitation in the consumer.

Thallus absorptance, daily courses of maximal quantum yields of chlorophyll fluorescence of photosystem II (F v /F m ) and electron transport rates (ETR) were determined in 3 macroalgae (Hypnea spinella, Rhodophyta; Sargassum vulgare, Phaeophyta; and Ulva lactuca, Chlorophyta) collected from a low nutrient supply (LNS) ecosystem (Red Sea, Gulf of Aqaba, Eilat, Israel). In addition, U. lactuca grown previously in high nutrient supply (HNS) fishpond effluents was used to evaluate the effect of nutrient enrichment on photosynthesis. Short-term (2 d) and mid-term (5 d) effects of both photosynthetically active radiation (PAR) and full solar irradiance (PAB: PAR+UVA+UVB) at 3 solar irradiance treatments (no neutral filters, no NF; 2 neutral filter layers, 2NF; and 4 neutral filter layers, 4NF simulating levels of irradiance at 5, 10 and 20 m depth respectively) were evaluated in algae incubated with running seawater. Significant effects of time (variation throughout the day) and irradiance (number of neutral filters) on both F v /F m and ETR were observed. Photoinhibition occurred at noon under the no NF (up to 40% decrease) and 2NF (up to 30% decrease) treatments; however, full recovery in all treatments was reached in the afternoon (dynamic photoinhibition) except in H. spinella. The highest maximum ETR was observed in the no NF treatment despite its strongest photoinhibitory effect. The decrease in F v /F m at noon was similar to or higher under the PAB than under the PAR treatment alone, depending on the species. Photoinhibition was lower and the maximum ETR was higher in HNS than in LNS U. lactuca, indicating positive effects of nutrient supply on both photosynthesis and photoprotection. The maximum ETRs exhibited by different algae may be related to their zonation in the field and the resulting energy supply.